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DnD 5e - Practical Guide to Multiclassing

Last Updated: September 25th, 2020

Introduction

Multiclassing is a powerful tool for character optimization. While individual classes work well on their own, sometimes exploring multiple classes can add some powerful new options to a character while also allowing you to explore interesting story ideas.

However, multiclassing is also complicated. Building a character already involes a large number of complicated decisions, and adding multiclassing to the mix can make the process intimidating, especially for new players. This article is written with two purposes: first, to explain multiclassing in terms that are clearer and more specific than those in the Player's Handbook; and second, to provide guidance on multiclassing options from a character optimization perspective.

How Does Multiclassing Work?

Multiclassing is actually pretty simple. It looks confusing and the text in the Player's Handbook has some gaps (which I'll fix below), but if you understand the core rules of advancing a single-class character you don't need to know much more to successfully advance a multiclassed character.

This page uses two terms which were used in previous editions of DnD, but don't exist officially in 5th edition. However, they're useful descriptors of concepts core to multiclassing, so I'm going to use them throughout the article.

  • Character Level: Your characters total number of levels across all of their classes. For a single-class character, your Character level is the same number as your Class Level.
  • Class Level: Your number of levels in a single class. For example, if Joe is a Fighter 3 / Rogue 1, their class level in Fighter is 3 and their class level in Rogue is 1.

Selecting a Class

When planning to multiclass, typically your first step is to consider which class you want to multiclass into. Every class has things to offer, so I'll go into more detail on suggestions later in this article. Provided that you meet the prerequisites, you can take levels in that class the next time you would gain a level.

Keep in mind that you can't take the same class more than once. You can't multiclass into a class in which you already have levels. No Rogue 1 / Rogue 1. I see new players ask about that a lot.

Prerequisites

There are some prerequisites to multiclass into every class. Typically, all that's required is an ability score of 13 or better in one or two ability scores which the class is dependent upon. See the Customization Options chapter of the Player's Handbook for the table of multiclass prerequisites. For the Artificer, see the Artificer class description in Eberron: Rising from the Last War.

Experience Points

Experience points are based on your character level, and that doesn't change regardless of how many classes you have.

Hit Points and Hit Dice

Hit Points are additive: As you gain levels, you'll roll for hit points (or take the rounded average, which you should always do) and add them to your hit point maximum just like if you gained a level in your original class. Remember that you use the "Hit Points at Higher Levels" entry for your class rather than the "Hit Points at 1st Level" entry. "Hit Points at 1st Level" refers to your character level, not your class level.

Hit Dice are similarly additive. Every time you gain a level in a class, you add a hit die of the appropriate size to your pool of hit dice. This will often result in having multiple hit die sizes. When you spend a hit die, you can choose which die to use. But the hit dice aren't interchangeable: if you only have one d12 hit die (such as from one level in Barbarian) and the rest are d6's (such as from several levels in Wizard), you only get to use the d12 hit die once per day.

Proficiency Bonus

Proficiency Bonus is based on your character level. While it's included in every class's class features table, it advances based on the sum of your levels rather than your level in a single class. If you multiclass, your Proficiency Bonus is still just as good as everyone else's.

Cantrips

Knowing a cantrip can come from a variety of sources: your race, your class, a a feat, or maybe your DM just gave it to you or something. Cantrips, like Proficiency Bonus, advance based on your character level. No matter how many classes you take, your damage-dealing cantrips will add more damage at character levels 5, 11, and 17. If you multiclass late in your career, your damage is still based on your character level, so if you spend your 20th level to take one level of Wizard you're suddenly very good at cantrips.

Ability Score Increases

Ability Score Increases are a class feature. While most classes gain Ability Score Increases at 4th, 8th, 12th, 16th, and 19th level (Fighters and Rogues both get more), it's still a class feature. It is entirely possible to multiclass so much that you never gain an Ability Score Increase.

Proficiencies

When you multiclass into a new class, you don't get everything which you would normally get from being a 1st-level character of that class. You do get everything listed in the class features table for the class, but you'll typically get a reduced set of the class's initial proficiencies (armor, skills, tools, weapons, etc.), and you never gain new starting equipment or saving throw proficiencies when you multiclass into a new class unless the class grants a feature that gives you additional saving throw proficiencies like the Rogue's Slippery Mind.

Keep in mind that duplicate proficiencies do not get replaced or upgraded or anything like that. If you get proficiency in medium armor twice, you're still just proficient in medium armor. If you get proficiency in Stealth twice, you're still just proficient in Stealth. The rule which allows you to replace redundant proficiencies is specific to backgrounds, and applies only to proficiencies granted by your background.

See the Customization Options chapter of the Player's handbook for the table of which proficiencies you gain from multiclassing.

Class Features from Multiple Classes

Several classes grant features with the same name. When this happens, there are some specific rules for some of these features. The Player's Handbook details Channel Divinity, Extra Attack, and Unarmored Defense but I've added some additional class features which new players often find confusing.

  • Ability Score Increases: Ability Score increases are independent of one another. You can gain as many as you can squeeze out of 20 levels.
  • Channel Energy: You don't get more uses between rests, but you can add additional ways to use it.
  • Cantrips: Cantrips known are additive, but remember that the source that gives you the cantrip determines the ability score which you use with that spell. For example: a High Elf Cleric / Wizard would get one cantrip from their race and a few from each class. You could select Toll the Dead from all three sources technically (don't do that) and you would have the ability to cast it using both Wisdom (Cleric) and Intelligence (High Elf or Wizard).
  • Extra Attack: The wording of Extra Attack very specifically doesn't add an attack; it replaces the number of attacks you can make. If two sources say "you can make two attacks", you can still only make two attacks.
  • Unarmored Defense: Unarmored Defense provides new calculation methods for determining your AC, just like donning armor or having natural armor from your race. You can choose which AC calculation to use (generally you'll want to use the highest), but you still only get to use one at a time.

Spellcasting / Pact Magic

The rules for spellcasting for multiclassed characters are detailed, and it's important that you read the original source text. I can't reproduce it here because it's not part of the SRD, so please see the Player's Handbook.

One interesting note: All of the partial spellcasters in the Player's Handbook (paladins, arcane tricksters, etc.) round their levels down when calculating your effective level for the purposes of spellcasting. The Artificer rounds up, and currently they're the only class to do so.

Should I Multiclass?

Now that you understand how multiclassing works, it's time to ask yourself an important question: Should I multiclass?

Generally, no. A single-class character is usually perfectly fine. While multiclassing is a great way to get something different for your character, it's not guaranteed to be something better than what you would get from a single class.

That said, if you do multiclass you can find a great number of powerful new options to improve your character.

When Should I Multiclass?

This question has two meetings: "When should I choose to make a multiclass character?" and "when in my character's level progression should I multiclass?", but that doesn't fit well into a section heading.

You should multiclass when you're looking to address a gap in your character's capabilities, such as poor action economy, low AC, or new spellcasting options. As explained above, many characters work fine as a single-class character, but sometimes new class features can really add a lot to your character.

When to begin taking levels in a new class is more complicated. It's tempting to start looking at other classes right at level 2, and sometimes that's okay to do. But be careful about what happens at level 5. Level 5 brings powerful options like Extra Attack and 3rd-level spells like Fireball, and the game's math is designed to respond to that sharp increase in player characters' capabilities with an equivalent jump in difficulty. If you postpone crucial features like Ability Score Increases, Extra Attack, and high-level spells, you may have trouble with high-CR foes. If you do choose to multiclass, be sure that whatever you get in exchange will offset whatever you give up or postpone.

How Many Levels Should I Take in Each Class?

This is probably the second-hardest question, right behind "which class do I take?", and it has a similarly frustrating answer: it depends on your build.

Players will commonly take what I refer to as a "class dip", where they take a small number of levels in a class before moving on to another class or back to their original class. This is often an effective way to build a multiclassed character because classes often grant several powerful features in their first few levels.

Sometimes you'll instead want to alternate sets of levels between two classes. This is less common because it often results in being bad at two classes rather than really good at one with some goodies from another, but I have seen a handful of builds where it makes sense.

Classes have some logical "break points" where it often makes sense to break away from that class. This is typically after you get some specific class features like the class's initial subclass features or an Ability Score Increase. I'll discuss break points for each class in the Classes and Subclasses section, below.

Classes and Subclasses

Below I'll discuss each class and subclass and what they can offer other classes. There are few truly bad options since nearly every class and subclass has something to offer, but not every class/subclass will add something useful to every build. I'll list numbered bullets with break points and explain why you might advance to that level before switching away from the class.

If you're building a new character and planning to multiclass at some point, I encourage you to explore the section below now. Starting with a level in a class changes your character a great deal, and even if you never take another level in that class a 1st-level class dip can be a great build choice.

Disclaimer

RPGBOT uses the color coding scheme which has become common among Pathfinder build handbooks, which is simple to understand and easy to read at a glance.

  • Red: Bad, useless options, or options which are extremely situational.
  • Orange: OK options, or useful options that only apply in rare circumstances.
  • Green: Good options.
  • Blue: Fantastic options, often essential to the function of your character.

I will not include 3rd-party content, including content from DMs Guild, even if it is my own, because I can't assume that your game will allow 3rd-party content or homebrew. I also won't cover Unearthed Arcana content because it's not finalized, and I can't guarantee that it will be available to you in your games.

Artificer

Artificers are a great class dip for many spellcasting classes both becuase of their unique rules for multiclassing, access to medium armor and shields, and because they get proficiency in Constitution saving throws, not to mention a number of fantastic class features which essentially any character can use.

  1. Magical Tinkering, Spellcasting: Magical Tinkering doesn't do much, but the Artificer's spellcasting includes a lot of options from the Wizard's spell list, and notably you get to round Artificer levels up when you calculate your effective level for determining your spell slots. The Artificer gets ritual casting, and they get access to healing spells like Cure Wounds and Healing Word, so for spellcasters like the wizard a single level offers a lot to like.
  2. Infuse Item, 2 Infused Items: Infuse Item is really good, but unless you make it to level 6 the options are very limited. However, staple options like Enhanced Arcane Focus, Enhanced Defense, and Replicate Magic Item offer enough options that you can easily find 2 options to use to good effect. For help, see my Artificer Handbook.
  3. Artificer Specialist, The Right Tool for the Job: The benefits of your Artificer Specialist vary. The Right Tool for the Job is situational, but can be useful for a class that's so good with tools.
  4. Ability Score Increase: Every class gets an Ability Score Increase at 4th level, and if you already took three levels in the class it's often very tempting to take one more just to get the ASI.
  5. Artificer Specialist feature: Varies.
  6. Tool Expertise, 3 Infused Items: Tool Expertise is neat, but you're probably here for the additional Infused Item and the additional Infusion options.
Alchemist

Nothing good enough to justify the opportunity cost of multiclassing.

  1. Tool Proficiency, Alchemist Spells, Experimental Elixir: The spells are nothing new to the Artificer's spell list. Experimental Elixir is a neat way to turn your 1st-level spell slots into some new effects, but it's not good enough to justify multiclassing for three levels.
  2. Alchemical Savant: A nice bonus to common damage spells and to healing spells, but compared to taking more levels in a class with full spellcasting (sorcerer, wizard, etc.) it's not worth the levels.
Artillerist

Three levels to get an Arcane Cannon can be a powerful asset, even if you don't have a lot of Intelligence to throw around. Arcane Cannon is that good.

  1. Tool Proficiency, Artillerist Spells, Eldritch Cannon: The spells are nothing new to the Artificer's spell list. You're here for Eldritch Cannon. Even if your Intelligence is mediocre, the Protector option is still spectacular. If you're built around Intelligence, the Flamethrower and Force Ballista options both work fine even with only three levels in artificer. Even the Wizard might find Eldritch Cannon a better use of a 1st-level spell slot than most spells. If you don't want to pour spell slots into replacing cannons, leave yours out of combat and it's still effectively castinf False life on your whole party before every encounter.
  2. Arcane Firearm: Tempting, but for a full spellcaster this isn't good enough to justify giving up two levels of your main class's spellcasting and the additional spell level which it grants.
Battle Smith

Battle Ready is the primary reason to multiclass into Battle Smith. It's an interesting option for Intelligence-based arcane/martial subclasses (arcane trickster, etc.), but it won't always fix your MAD problems, and you need to consider if giving up 3 to 4 levels in your primary class and postponing your class's high-level class features is worth having a better Intelligence bonus to back up your spells without sacrificing your attack bonus.

  1. Tool Proficiency, Battle Smith Spells, Battle Ready, Steel Defender: There are two notable things here: Battle Ready and Steel Defender. Battle Ready is tempting for arcane trickster, eldritch knights, and bladesingers who all typically need to balance their ability scores between either Strength or Dexterity and Intelligence. However, your Steel Defender is much less useful since its hit points are calculated based on your artificer class level.
  2. Extra Attack: Arcane tricksters and bladesigners might decide that 2 more levels to get Extra Attack is worth the cost, but I would think long and hard about how desperate you are to make a second attack compared to what you give up.

Barbarian

The Barbarian is a tempting class dip for martial characters or for other classes which want to improve their martial capabilities beyond what their class offers` on its own. However, it can also be a difficult option because there are so few boring levels in the class so it's hard to pick a break point.

  1. Rage, Unarmored Defense, 2 Rages: Two great reasons to take a barbarian dip. Unarmored Defense is a great option for many martial builds, though it won't exceed the AC from armor until you've acquired several Ability Score Increases. One level only gets Rage twice per day, but when you need help with Strength checks or you just need a little extra damage it's still a great combat buff.
  2. Reckless Attack, Danger Sense: Reckless Attack is a great offensive option, but other classes may bot be durable enough to risk constantly granting Advantage to hit them. Many rogues eye Reckless Attack, but remember that it only works with melee attack rolls using Strength. Danger Sense is similarly tempting if you combine it with the Rogue's Evasion, granting you near immunity to many AOE damage effects. Danger Sense is less useful for other classes, but AOE damage is still very common so it's still very useful.
  3. Primal Path, 3 Rages: Varies by Primal Path. You also gain a 3rd rage per day at this level.
  4. Ability Score Increase: Every class gets an Ability Score Increase at 4th level, and if you already took three levels in the class it's often very tempting to take one more just to get the ASI.
  5. Extra Attack, Fast Movement: Extra Attack is a central feature of most martial classes, but by this level you should probably think about making barbarian your primary class. Fast Movement is nice, too, and most marti classes don't grant anything except Extra Attack at 5th level.
  6. Path Feature, 4 Rages: Varies by Primal Path. You also gain a 4th rage per day.
Ancestral Guardian

  1. Ancestral Protectors: One of very few "taunt" mechanics in the game, this is a great way to force enemies to focus on your in combat. You also get 3 rages per day at this level, so you can employ this several times throughout the day.
  2. Spirit Shield (2d6): This is good, but it's not good enough to justify multiclassing 6 levels.
Battlerager

The AC lost when you compare Half Plate to Spiked Armor is likely not worth the Bonus Action attack which you get in return. If you're desperate for an additional way to spend your Bonus Action, consider a level of Monk for Martial Arts or try two-weapon fighting.

  1. Battlerager Armor: Battlerager Armor is bad medium armor. It gets you a Bonus Action attack which sounds tempting, but if you want to use a two-handed weapon with a Bonus Action attack, take one more level and get Polearm Master with the level 4 Ability Score Improvement.
  2. Reckless Abandon: Up to 5 temporary hit points every round when you decide to use Reckless Attack. This is a nice pad to your hit points, but it's nowhere near good enough to take 6 levels of barbarian to get it.
Berserker

Frenzy is the most likely reason why you might consider Path of the Berserker, but you're unlikely to use it more than once per day, and if you do use it you're going to regret it for the rest of the day, so you're spending 3 levels to get a class feature that you're going to regret using.

  1. Frenzy: Frenzy is hard choice for the Barbarian because Exhaustion can be a serious problem due to its increasing effects as you add levels of Exhaustion. As your number of rages per day increases, the temptation to take on more and more levels of exhaustion grows, and since exhaustion only wears off one level per long rest, it can be a multi-day endeavor to recover from a few uses of Frenzy. But if you only go a few levels into barbarian and only have 2 or 3 rages per day, Frenzy is much less of a problem since it's so much harder to rack up levels of exhaustion. If you just need a good combat buff once or twice a day, Frenzy is a viable option so long as you can handle having 1 or 2 levels of exhaustion afterward. But if you just need a once per day combat buff, 3 levels in barbarian is a terrible way to get it.
  2. Mindless Rage: Charm and Fear effects are common and they're great ways to take a martial character out of a fight since martial characters typically have poor mental saves. But I don't think it's good enough to go this far into the Barbarian to get it.
Storm Herald

Storm Aura is too dependent on barbarian class level to make it viable for a multiclassed character.

  1. Storm Aura: This is a really great class feature, but the effects scale with barbarian class level so unless you're a single-class barbarian the effects will gradually become less and less appealing as you gain levels.
  2. Storm Soul: Basically just damage resistance to one damage type. Not worth the levels.
Totem Warrior

Three levels of Path of the Totem Warrior gets you the first totem ability, which adds a powerful additional effect to your Rage.

  1. Spirit Seeker / Totem Spirit: Spirit Seeker is very situational, but that's not why you're here. Totem Spirit adds an additional effect to your rage, and with 3 rages per day that can be a big tactical option. Generally people will go for Bear for the additional damage resistances, but in a party with other melee allies don't overlook Wolf.
  2. Aspect of the Beast: These abilities are almost entire "flavor" abilities with very little substance.
Zealot

Path of the Zealot is already a niche option for death-prone players, and multiclassing into it doesn't make it better.

  1. Divine Fury, Warrior of the Gods: Divine Fury is too dependent on class level, and Warrior of the Gods is only appealing if you die frequently and don't like building replacement characters.
  2. Fanatical Focus: Great, but less useful since you're not going to continue to get additional rages per day.

Bard

A tempting option for any Charisma-based character, especially spellcasters, the Bard's unique mix of spellcasting, skill mastery, and support features makes them a great way to broaden your skillset without a big level investment. Bard subclasses are diverse, offering numerous ways to improve various capabilities depending on what you want from your class dip.

Even for non-Charisma character, the Bard has a lot to offer between extra proficiencies, spellcasting (including ritual casting), and numerous powerful low-level class features, many of which use your Bonus Action or work outside of combat so they won't conflict with most of your other class features.

  1. Spellcasting, Bardic Inspiration (d6): If you have decent Charisma, a single level of bard gets you quite a bit. Light armor (great for sorcerers), proficiency in any one skill and and instrument, plus some staple bard features.

    Bardic Inspiration is just incredibly useful, and even if you never improve the die, increasing your Charisma will add more uses so it's a great option for other Charisma-based spellcasters like paladins, sorcerers, and warlocks, as well other characters who might have high Charisma like some rogues.

    The Bard's spellcasting at 1st level isn't going to be stunningly powerful, but it includes some great healing and support options like Healing Word and Heroism, and you do get ritual casting with the handful of bard spells that you learn.

  2. Jack of All Trades, Song of Rest (d6): Song of rest is always nice, but beyond low levels the extra d6 will quickly feel like an insignificant addition to other healing during a Short Rest. It's like sprinkles on top of a big bowl of ice cream: It looks nice and it feels nice, but it's not really doing much at that point.

    Jack of All Trades is why you're really here. Ironically, it's more useful with skills if you have fewer skill proficiencies so it's a great option for multiclassed characters who didn't start as a bard or rogue, but its benefits don't stop with skills. I've found a long a list of other cases where it applies and they're listed on my Bard Handbook.

  3. Bard College, Expertise: The benefits of your bard college will vary by college. Expertise is useful on nearly every character, and you get to pick two proficiencies. If you're not sure, Perception is always a good choice.
  4. Ability Score Increase: Every class gets an Ability Score Increase at 4th level, and if you already took three levels in the class it's often very tempting to take one more just to get the ASI.
  5. Bardic Inspiraton (d8), Font of Inspiration: If you've been enjoying Bardic Inspiration, this is a great level. Not only does the die size increase, but your pool of dice resets on Short Rests so you can get as many as three times your Charisma Modifier per dau (assuming that you're using the Adventuring Day rules).
  6. Countercharm, Bard College Feature: Countercharm is very situational, so you're taking this level for your subclass feature.
College of Eloquence

Literally everything you get is fantastic, and relying more on Charisma makes it progressively better. If you're going for a bard dip and don't know what else to take, College of Eloquence is a great choice.

  1. Silver Tongue, Unsettling Words: This is a good level for any Face character, but it's a great level for any spellcaster. Sure, your Bardic Inspiration die is only a d6, but the average roll on a d6 is 3.5 and Disadvantage works out to a penalty slightly worse than -3, which means that you can impose a penalty which is on average larger than Disadvantage as Bonus Action, then follow it up with a spell as an Action.
  2. Unfailing Inspiration, Universal Speech: Unfailing Inspiration is a major improvement to Bardic Inspiration, and Universal Speech is fantastic on any Face character.
College of Glamour

Mantle of Inspiration is an interesting option if you multiclassed into bard but don't want to invest in Charisma and Face skills to make College of Eloquence's features more appealing. Other than that, there's very little here worth having.

  1. Mantle of Inspiration, Enthralling Performance: Mantle of Inspiration is an interesting tactical option, but I've always found Enthralling Performance to be very difficult to use.
  2. Mantle of Majesty: Absolutely not worth this many levels.
College of Lore

If you need better Face skills, go for College of Eloquence. If you just want more skill proficiencies, College of Lore is a good choice.

  1. Bonus Proficiencies, Cutting Words: Three more skill proficiencies of your choice. Cutting Words offers a useful way to apply Bardic Inspiration defensively without spending the Bonus Action ahead of time to give your ally an inspiration die.
  2. Additional Magic Secrets: The point of Magic Secrets is to enable the Bard to get access to other class's spells without multiclassing. If you're taking 6 levels of bard to get 2 spells from another class, why not just take levels in that class?
College of Swords

This is a really hard choice. You'll get better proficiencies from the Fighter with better Fighting Style options, and the Battle Master Fighter's Superiority Dice offer considerably more tactical options with a similarly-sized pool that recharges on a Short Rest right from 3rd level. If you want spellcasting, other sublcasses or even other classes offer better options. If you need both martial proficiencies and spellcasting from one class, I'm not sure what your base class is. Maybe rogue? I could see an Arcane Trickster build here, but it's difficult to justify.

  1. Bonus Proficiencies, Fighting Style, Blade Flourish: The proficiencies seem silly in the face of other multiclass options, but you can use weapons as spellcasting focuses and you get a Fighting Style, both of which are appealing for characters looking to balance martial prowess and spellcasting. Blade flourish is thematically interesting, but it eats your Bardic Inspiration dice so it's hard to recommend using it unless you go far enough to get Font of Inspiration.
  2. Extra Attack: A level later than martial classes on top of how long you may have postponed it to multiclass.
College of Valor

The only reasons I can think of to pursue College of Valor on a multiclassed character are for the armor and shield proficiencies without giving up the spellcasting progression. If that's all that you need, take a level of cleric.

  1. Bonus Proficiencies: If you're already multiclassing and you want medium armor and martial weapons, a level of fighter is typically a better choice. However, fighter won't advance your spellcasting so in some builds this may make sense.
  2. Extra Attack: Essential on any martial character, but valor bards get it a level late and multiclassing into bard to get it this late seems incredibly unwise.
College of Whispers

Words of Terror is the best that College of Whispers can offer a multiclassed character, and it's not easy enough to use to justify.

Psychic Blades has an interesting place in novelty builds around "smite" mechanics, but on a build you actually plan to play it's not worth the Bardic Inspiration die to activate it.

  1. Psychic Blades, Words of Terror: Psychic Blades already isn't a great ability and it's very dependent on class level. Words of Terror is neat, but really hard to bring into play.
  2. Mantle of Whispers: Not good enough to justify this many levels. Just cast Disguise Self.

Cleric

Despite their role as the iconic divine spellcaster, the Cleric is an interesting class dip for numerous classes. Despite the proficiencies gains from multiclassing into cleric, you can use Divine Domain to get heavy armor proficiency with a single level, not to mention adding powerful low-level cleric spells like Bless and Healing word to your spellcasting options.

Despite their excellent 1st-level and 2nd-level benefits, clerics have several "dead levels" where you get nothing noteworth except spellcasting advancement, which can make it hard to justify going past low levels.

  1. Spellcasting, Divine Domain: Clerics have a lot of really great 1st-level spells, and Divine Domain allows you to choose from an unusually broad list of options since there are more Divine Domain options than any other type of subclass.
  2. Channel Divinity (1/rest), Divine Domain Feature: Turn Undead trivializes encounters with undead, and even if you never use Channel Divinity for anything else, take comfort knowing that a very common creature type is considerably less threatening.
  3. Ability Score Increase: Every class gets an Ability Score Increase at 4th level, and if you already took three levels in the class it's often very tempting to take one more just to get the ASI.
  4. Channel Divinity (2/rest), Divine Domain Feature: Varies by subclass.
Arcana

I can't figure out who would benefit from this. If you want wizard spells and don't want to be a cleric, play a wizard.

  1. Domain Spells, Arcane Initiate: If you want wizard spells, multiclass into wizard. The only excuses I can think of is that you want wizard cantrips but cleric leveled spells or that you want wizard spells but you want to cast them using Wisdom. Maybe this is appealing for druids?
  2. Channel Divinity: Arcane Abjuration: Situational. If it works, it can remove a single target from a fight temporarily. But it only targets four creature types, so you can't rely on it being useful, and unlike Turn Undead it's single-target so it won't suddenly trivialize an encounter by making half of your enemies run away while you kill the rest.
  3. Spell Breaker: Provided that your other levels advance your spellcasting, you can upcast Healing Word at whatever leve lyou need to remove a spell on an ally.
Death

Reaper is a nice addition for School of Necromancy wizards, but beyond that I see very little reason why other classes would consider it.

  1. Domain Spells, Bonus Proficiency, Reaper: Proficiecy in martial weapons isn't why you're here. You're here for Reaper so that you can hit two targets with Chill Touch and with Toll the Dead.
  2. Channel Divinity: Touch of Death: Too dependent on class level.
  3. Inescapable Destruction: Tempting, but if you want to be necrotic-damage base blaster you likely need to stick to cleric levels.
Forge

Great for a 1-level dip, but otherwise uninteresting.

  1. Domain Spells, Bonus Proficiencies, Blessing of the Forge: Heavy armor proficiency and a free +1 armor/shield/weapon. If you're not going any further than level 1, this is a really great choice.
  2. Channel Divinity: Artisan’s Blessing: Very situational.
  3. Soul of the Forge: Not worth the levels. If you just want +1 AC take a level of fighter for Fighting Style. If you want fire resistance, cast Absorb Elements.
Grave

Grave Domain is a good option for the Cleric, but it's a hard choice for a multiclass build. It doesn't offer anything that's going to support a multiclass build, and while the features aren't directly dependent on class level they generally improve by being a higher-level cleric and increasing your Wisdom.

  1. Domain Spells, Circle of Mortality, Eyes of the Grave: The healing benefit of Circle of Mortality is nice because the most important time to heal an ally is when they're at 0 hit points. Hit them with Healing Word, and they'll get a few more hit points than they usually would. This won't be a big mathematical improvement, but it feels nice. Spare the Dying as a Bonus Action is neat, but rarely important since you should be using Healing Word at that point. Eyes of the Grave is very situational.
  2. Channel Divinity: Path to the Grave: You want to follow this with the biggest single hit that your party can muster. This will be much better if you make it to 6 levels and can use it twice per rest, and unfortunately it's very hard to capitalize on by yourself.
  3. Sentinel at Death’s Door: Few builds will have enough Wisdom to make this impactful.
Knowledge

The Knowledge Domain doesn't give you anything which you couldn't find elsewhere, and typically other options will have more to offer.

  1. Domain Spells, Blessing of Knowledge: Proficiency and expertise in two knowledge skills. Neat, but not the sort of impactful new capability which justifies a class dip unless your entire build is about being good at knowledge skills.
  2. Channel Divinity: Knowledge of the Ages: An interesting way to handle proficiencies which your party lacks, but if you're multiclassing to get this feature you'll get more form the Bard's Jack of All Trades.
  3. Channel Divinity: Read Thoughts: Reading a creature's thoughts and hitting them with Suggestion can be very effective, but it's not worth 6 levels of cleric.
Life

The Life Domain is a frustrating multiclass option because it presents a paradox: it makes you better at casting healing spells, but that's only meaningful if you cast lots of healing spells; and if you're already casting lots of healing spells, why do you need to multiclass into cleric? There may be some builds like Divine Soul Sorcerer which can benefit from Life Domain's features, but even then I'm not sure why you would go the trouble to multiclass instead of just playing a Life Cleric. If you do go this route, I woudln't go more than one level.

  1. Domain Spells, Bonus Proficiency, Disciple of Life: Heavy armor is great, but Disciple of Life is only a meaningful improvement to healing spells if you cast a lot of them or if you have healing spells which provide repeated healing like Healing Spirit or which heal multiple creatures like Mass Healing Word. If your healing options come entirely from a few levels of cleric, Disciple of Life won't have a meaningful impact.
  2. Channel Divinity: Preserve Life: While this is a big pile of healing from the Cleric, it scales based on class level, so it's not a good option for multiclassed characters.
  3. Blessed Healer: Similar to Disciple of life, this is much less useful unless your primary class has abundant healing options to capitalize on the effects.
Light

The only reason to consider the Light Domain is Warding Flare, and aside from clerics and druids no one has Wisdom high enough to justify it.

  1. Domain Spells, Bonus Cantrip, Warding Flare: Warding Flare is a great defensive option, but the uses are limited and since you get uses equal to your Wisdpm modifier the characters most likely to use this are Wisdom casters. Unfortunately, there are only two Wisdom casters and clerics are half of them. So: is Warding Flare and access to 1st-level cleric spells worth taking a level away from Druid? Maybe. Clerics get a lot of great spells at 1st level.
  2. Channel Divinity: Radiance of the Dawn: Too situational.
  3. Improved Flare: Fantastic, but not worth 6 levels.
Nature

The primary reason to pursue Nature is to get heavy armor and a druid cantrip in one level. There are absolutely

  1. Domain Spells, Acolyte of Nature, Bonus Proficiency: In a lot of cases, Acolyte of Nature is going to be used to get Shillelagh. Turning your Wisdom into your attack stat means that you can easily disregard Strength and focus on Wisdom so that you can be really good at spellcasting and melee attacks at the same time. Combine that with heavy armor and shields, and one level of Nature Cleric can turn a high-Wisdom character into a martial threat. Unfortunately, there are few classes who can actually benefit from that combination. Druids already get Shillelagh and generally can't use heavy armor since it's all metal. Monks can't wear armor, so they need high Dexterity anyway so Shillelagh is a waste of a Bonus Action in most cases. Rangers typically need high Dexterity to support Stealth, so heavy armor isn't a great choice. The Ranger is probably the best use case or this ability, but if you're going to build a heavily armored high-Wisdom ranger, you're essentially building a worse nature cleric. You could consider Shillelagh for Polearm Master builds, but unless you're going to depend on Wisdom it doesn't add much.
  2. Channel Divinity: Charm Animals and Plants: Too situational. Plant and animal creatures stop appearing around CR 12, and even in the ranges where they exist charming them doesn't give you the ability to speak to them.
  3. Dampen Elements: Spectacular, especially since there's no usage limitation beyond your Reaction, but almost certainly not worth 6 levels.
Order

For a spellcaster taking a 1-level dip into cleric, Order Domain is a fantastic choice. The Sorcerer's Font of Magic feature can be easily abused to turn your high-level spell slots into 1st-level spell slots to power Voice of Authority, allowing you to repeatedly give your party's most deadly weapon user additional attacks at an alarmingly low resource cost. You also get heavy armor, which is really nice on a squishy character like a sorcerer.

  1. Domain Spells, Bonus Proficiencies, Voice of Authority: A truly spectacular level for support casters. Heavy armor is great, and Voice of Authority allows you to give your allies a free weapon attack when you target them with a spell (though only one ally gets the effect). If you're primarily a spellcaster, you'll have enough spell slots to trigger this repeatedly, and if you have allies who rely on small numbers of big attacks (barbarians, rogues, etc.) an extra attack can provide a massive amount of damage output. Look for inexpensive low-level spells which you can use on your allies like Healing Word and Heroism. Abusing this ability will eat your 1st-level spell slots, so consider some levels in Sorcerer to get Font of Magic so that you can turn higher-level slots into cost-efficient 1st-level spell slots.
  2. Channel Divinity: Order’s Demand: If you have sufficient Wisdom to back this up, it can be effective both in and out of combat. However, the duration is only until the end of your next turn so you need to act quickly to capitalize on it.
  3. Embodiment of the Law: Unless you're built around Wisdom (and very few characters are), you won't be able to use this frequently enough to justify this many levels.
Tempest

Another option where you get heavy armor but need good Wisdom to make effective use of everything you get. Blasters might enjoy Channel Divinity: Destructive Wrath to boost lightning/thunder damage spells, but one use per day may not be worth two levels.

  1. Bonus Proficiencies, Wrath of the Storm: Martial weapons and heavy armor can do a lot to add martial capabilities to your build, but Wrath of the Storm needs high Wisdom to make it work meaningfully. If druids could use metal armor this would be great, but it's hard to think of other builds which would make this work.
  2. Channel Divinity: Destructive Wrath: Other classes including the Bard, the Druid, the Sorcerer, and the Wizard all have access to spells which deal lightning or thunder damage. Storm sorcery sorcerers might find this especially tempting.
  3. Thunderbolt Strike: Interesting, but not worth 6 levels. If you're really into Destructive Wrath you might want the second use of Channel Divinity, but 4 more levels in your primary class will almost certainly be more effective.
Trickery

This would be an interesting option for a rogue or a similarly stealthy character looking to add some support capabilities and some magical options.

  1. Blessing of the Trickster: A great way to solve the challenge of noisy allies, but if you're taking a level of cleric to keep your allies from ruining your Stealth checks you should spend more time thinking about your tactics rather than spending a level just for this ability.
  2. Channel Divinity: Invoke Duplicity: This is a fun, deceptive option but the ability to cast spells through the duplicate is a difficult prospect unless you already have enough spellcasting to make it an interesting option.
  3. Channel Divinity: Cloak of Shadows: Definitely not worth 6 levels.
War

If you want a quick dip into cleric to pick up better proficiencies, War Domain is the best way to do it for martial characters. War Priest is a great option even if you only have the required 13 Wisdom to multiclass into cleric, so the extra that you get on top of the proficiencies will still feel satisfying even if your Wisdom isn't great.

  1. Bonus Proficiencies, War Priest: Martial weapons, heavy armor, and an extra attack a few times per day. If you need the extra proficiencies, this probably your best way to get it across any class. War Priest's usage count is Wisdom-based, but if you already have good uses for your Bonus Action you should think of this as an occasional boost to your damage output rather than a tactical option which you can rely upon constantly. The fact that it's just a normal attack means that even if your Wisdom is awful the attack is still useful so you're still getting something meaningful out of the ability.
  2. Channel Divinity: Guided Strike: This can be really great if you only get one high-damage attack each round, but with only one use of Channel Divinity per short rest it's not a big improvement to your capabilities.
  3. Channel Divinity: War God's Blessing: You'll have two uses of Channel Divinity, but you're still more likely to save this for yourself so this isn't a big improvement.

Druid

Druid are a difficult choice as a multiclass option. Their class features are often heavily dependent on class level, and even one level in the class disallows metal armor so anything more protective than studded leather is off limits.

  1. Druidic, Spellcasting: This is a terrible level. Druid spellcasting is fine, but Druidic is very situational so you're basically just getting the spellcasting. Access to some Druid-exclusive spells like Shillelagh and Goodberry is nice, but rarely worth a level when you can get them from Magic Initiate.
  2. Wild Shape, Druidic Circle: Wild Shape is a really neat ability with some interesting utility options, but it's not a good combat option if you're just dipping into druid, and you need to invest a lot of levels to enable swim speeds and eventually fly speeds.
  3. Ability Score Increase: Every class gets an Ability Score Increase at 4th level, and if you already took three levels in the class it's often very tempting to take one more just to get the ASI.
  4. Druidic Circle Feature: Varies.
Circle of Dreams

Nothing worth multiclassing to get.

  1. Balm of the Summer Court: Entirely dependent on class level. Similar in many ways to healing word, but without the scaling pool of dice this won't be useful compared to spells.
  2. Hearth of Moonlight and Shadow: There are a number of comparable solutions: Rope Trick, Tiny Hunt, Magnificent Mension. This is not unique or powerful enough to justify multiclassing.
Circle of Spores

If you have nothing better to do with your Reaction and you're frequently in melee, Halo of Spores is tempting. But it's not a ton of damage on its own, and you can't rely on Symbiotic Entity since the pool of temporary hit points is so small.

  1. Circle Spells, Halo of Spores, Symbiotic Entity: Halo of Spores appears to scale with character level rather than class level, but it's not clear if that's intentional and I can't find any sage advice, errata, or tweets on the subject. If it is dependent on character level, it's a small, but consistent and reliable source of damage output. However, it's also poison damage (which is commonly resisted) and the 10-foot range is dangerous unless you're built for melee.

    Symbiotic Entity is heavily dependent on class level. Your pool of temporary hit points is 4 times your druid class level, and symbiotic entity ends when those hit points go away. Unless you're using a ranged weapon, you're in melee drawing attacks and Symbiotic Entity could fall off at any point. Since activating Symbiotic Entity is an Action, it's unlikely that you'll activate it again during the same fight.

  2. Fungal Infestation: This ability isn't great on a single-class druid, and multiclassing doesn't make it any better.
Circle of the Land

Circle of the Land is great at being a single-class druid focused on spellcasting. If you're multiclassing into Druid, that's not you.

  1. Bonus Cantrip, Natural Recovery: Another cantrip isn't a huge boon if you're multiclassing intro druid, and Natural Recovery is hugely dependent on class level.
  2. Land's Stride: Too situational.
Circle of the Moon

Circle of the Moon is all about Wild Shape, and Wild Shape is extremely dependent on levels, so it's a terrible option for multiclassing.

  1. Combat Wild Shape, Circle Forms: Wild Shape is not a combat option for characters taking a class dip.
  2. Primal Strike: You should not invest this many levels to still be bad at using Wild Shape in combat.
Circle of the Shepherd

Spirit Totem is the most likely reason you would pursue Circle of the Shepherd, but a lot of its benefits are lost because they're dependent on class level. Mighty Summoner is hard to justify, and if you want to play a summoner a single-class Circle of the Shepherd Druid is likely your best choice.

  1. Speech of the Woods, Spirit Totem: Speech of the Woods is neat, but Speak with Animals is a 1st-level spell. Spirit Totem is neat, but Hawk Spirit is the only option that's not dependent on your class level, it only lasts one minute, and it only works once per short rest.
  2. Mighty Summoner: This is great for players who enjoy summon spells, but if you're taking 6 levels away from your primary class you're givng up access to higher-level summoning spells. You might be able to upcast your lower-level summon spells, but if you're built around summon spells why not just play a druid?

Fighter

Heavy armor, shields, and Constitution saves make the Fighter a tempting first level for spellcaster builds, and Fighting Style and Action Surge are popular for nearly any character. Fighter subclasses get excellent benefits at 3rd level, too. You can frequently find something fancier from other classes, but the Fighter is still an easy option to complement many builds.

  1. Fighting Style, Second Wind: Fighting Style and the fighter's proficiencies are a great reason to take a level of fighter, but generally you want to make that your first level so that you get heavy armor proficiency. Still, other martial classes which are already happy with their armor proficiencies will enjoy Fighting Style even if they already have one.
  2. Action Surge (1/rest): The ability to take a second action and do something like casting a second spell in your first turn in combat offers a lot of really great tactical options. But it's only once per rest, and you need to weight one additional Action one to three times per day (assuming that you use the Adventuring Day rules) and you need to weigh the ability to sometimes do an extra thing against abilities which might let you do something more effective. For example: is access to spells two levels higher better or worse than being able to cast an extra spell a few times per day? Sometimes the answer is "it depends" and you'll need to figure out that balance.
  3. Martial Archetype: Varies.
  4. Ability Score Increase: Every class gets an Ability Score Increase at 4th level, and if you already took three levels in the class it's often very tempting to take one more just to get the ASI.
  5. Extra Attack: Standard for most martial classes at this level. Fighters eventually get more attacks than anyone else, but that doesn't happen until 11th level.
  6. Ability Score Increase: Fighters get more Ability Score Increases than any other class. This is the first "extra" that you get, making it a great time to take a feat.
Arcane Archer

Potetially tempting for rangers and rogues built for archery, but otherwise not worth the levels. Go for Battle Master instead.

  1. Arcane Archer Lore, Arcane Shot (2 options): Arcane Archer Lore is neat, but particularly important. Arcane Shot is why you're here. On a character build around archery (such as a ranger or rogue) Arcane Shot can be tempting. You never get more than 2 uses per Short or Long Rest anyway, and the damage on the shots doesn't scale until 18th level so all that you're giving up is additional options to use your paltry 2 shots. Grab Grasping Arrow because it's insanely good and maybe Bursting Arrow because it's good for tightly-packed groups, but avoid everything else unless you have the Intelligence to keep your save DC really high.
Battle Master

If you have a martial character and want to do something more exciting than just swinging your weapon, this is a great addition. Combat Superiority adds numerous excellent tactical option which allow you do interesting things in combat without giving up your attacks.

  1. Combat Superiority, Student of War: Student of War is basically a throw-away. Combat Superiority is why people pick the Battle Master. The initial benefits give you 4 dice and 3 maneuvers, giving you some exciting tactical options for any martial character. You can also take the Martial Adept feat to expand this a bit without additional fighter levels. Keep in mind that while 4 dice can feel like a lot, they recharge on a Short or Long Rest, so you'll need to conserve them between fights rather than burning through them all in one turn.
Cavalier

You're here for Unwavering Mark, and you don't get to use it enough to justify three levels.

  1. Bonus Proficiency, Born to the Saddle, Unwavering Mark: Three levels for a skill proficiency, the ability to be slighter better at getting into and out of a saddle, and Unwavering Mark which provides an attack as a Bonus Action with a damage bonus dependent on your class level. This might be interesting on a paladin that really enjoys Find Steed or on a character with Fighting Style (Protection), but even then it's not great. You don't get to use Unwavering Mark enough to make it exciting, and that's the best part of this class dip.
Champion

The Champion is somewhat bland since the improvements it provides are purely mathematical, but scoring twice as many critical hits can be a huge increase in your damage output, especially if you have a class feature which adds additional effects or damage to critical hits.

  1. Improved Critical: Critical hits are really nice for martial characters, and since this doesn't require the attack to hit normally it also guarantees a hit on a roll of 19 or 20. Barbarians with brutal critical, Paladins with divine smite, rogues with Sneak Attack, and warlocks with Eldritch Smite can all benefit immensely from more frequent critical hits, and if you can get Advantage on attacks you have a significant change to score a critical hit on any given attack.
Echo Knight

Manifest Echo is insanely powerful. Honestly Unleash Incarnation on top of it is unnecessary. If Unleash Incarnation were removed from the subclass, this would still be blue because Manifest Echo is just that incredible.

  1. Manifest Echo, Unleash Incarnation: Manifest Echo is incredibly powerful. Unleash Incarnation is great, too, but Manifest Echo is just insanely good and incredibly easy to abuse. Avoid any options that rely on your Bonus Action because almost anything else that you could possibly do is going to be less important than doing something with your echo.
Eldritch Knight

The Eldritch Knight already does the job of removing the need to build a multiclassed fighter/wizard (though there are still great fighter/wizard builds), and bringing it into a multiclass build is typically a bad idea. However, if you're adding Eldritch Knight to a spellcaster build, it will progress your spellcasting (though very slowly) and access to wizard cantrips can offer some tempting offensive options like Booming Blade for other spellcasters who normally don't get those options.

  1. Spellcasting, Weapon Bond: Eldritch Knight spellcasting is basically just worse wizard spellcasting. Weapon Bond is neat, but it's not good enough to spend levels to get it.
Purple Dragon Knight / Banneret

Rallying Cry is neat, but too dependent on class level.

  1. Rallying Cry: Depends on your fighter class level. If you want a tiny bit of healing, take a level of Life Cleric.
Samurai

If you just want easy advantage, there are easier ways to get it.

  1. Bonus Proficiency, Fighting Spirit (5 temp. hp): Advantage on all attacks for one turn three times per long rest plus a tiny amount of temporary hit points. Maybe interesting when combined with Action Surge and really big attacks from a class that relies on numeorus attacks, but if you just want easy Advantage take two levels of barbarian for Reckless Attack. You can use this with more weapons than Reckless Attack, which may be enough to justify it. You also get a skill, but that's not why you're here.

Monk

Monks are the most MAD class in the game, dependent on three ability scores to survive their role as an almost exclusively melee striker. This lack of build flexability makes them challenging on their own, and bringing those challenges into a multiclass build is challenging. You can't wear armor or use a shield or you lose many of your monk class features, and that alone mandates a lot about your build. Still, classes which have overlapping ability score requirements can find a lot of benefits from levels in monk.

  1. Unarmored Defense, Martial Arts: Dexterity and Wisdom are a great combination of ability scores, useful for a variety of builds. Clerics, druids, rangers, rogues, and even some fighters and paladins can be built with high enough Dexterity and Wisdom to make the Monk's Unarmored Defense viable enough to replace armor. If you can handle that build choice, you're rewarded with AC that can go as high as 20 without a single item or spell. Martial Arts adds offensive capabilities, too. If you don't rely heavily on your Bonus Action already you can easily capitalize on the additional attack to add a lot of additional damage.
  2. Ki, Unarmored Movement: Ki is great, but you only get a number of points equal to your monk level so there is a huge incentive to take more monk levels. Unarmored Movement is great for a class that's as close to melee-only as you can get.
  3. Monastic Tradition, Deflect Missiles: The benefits of your Monastic Tradition vary, but Deflect Missiles is almost` never useful unless you face an abundance of humanoid enemies.
  4. Ability Score Increase, Slow Fall: An Ability Score Increase is always welcome, but Slow Fall almost never matters and it's redundant with Feather Fall.
  5. Extra Attack, Stunning Strike: Extra Attack is great, and Stunning Strike is a spectacular debuff if you have the Wisdom to keep the DC high.
  6. Ki-Empowered Strikes, Monastic Tradition Feature: If you've come to rely heavily upon your additional attack from Martial Arts, treating the attacks as magical means that you can handle foes with resistance to damage from non-magical attacks. Normally that requires a magic weapon or a spell or something like that.
Way of the Drunken Master

Too dependent on Ki to make it viable for a multiclass dip.

  1. Bonus Proficiencies, Drunken Technique: Drunken Technique means never choosing between Flurry of Blows and Disengage again, but with 3 Ki Points per Short or Long Rest it's not a big improvement.
  2. Tipsy Sway: Both effects are only situationally useful, but by this level you have 6 ki points per Short or Long Rest so you can actually afford to use Redirect Attack frequently.
Way of the Four Elements

Way of the Four elements is all about turning Ki into spells. Multiclass characters don't have enough Ki to make that viable.

  1. Disciple of the Elements: You won't have enough Ki to make this good.
  2. Additional Elemental Discipline: If you've gone this far you've made a terrible mistake.
Way of the Kensei

The only reasons I can think of to explore Wai of the Kensei is for either the +2 AC from Agile Parry or because you want to get a d10 melee weapon and attack using Dexterity instead of Strength. But you can get similar functions from other places, and the damage difference between a rapier at 1d8 and a longsword in two hands at 1d10 is not worth three levels unless you're also adding Great Weapon Master to the mix.

  1. Path of the Kensei (2 weapons): Kensei Weapons allows you to attack with several non-Finesse weapons using Dexterity instead of Strength, and use Martial Arts on top of that. You could use a longsword two-handed to get a d10 damage die, which is the best that the Monk can get. Unfortunately, Agile Parry requires that you make an unarmed strike as part of the Attack action, so until you get Extra Attack your weapon is basically just a pointy decoration. Agile Parry is really good, but the fact that you're forced to use the Martial Arts damage of a 3rd-level monk to get it means that you're giving up the reason you're probably here. If you just want +2 AC, grab a shield. Kensei's Shot is also here, but the extra d4 damage is meant to make you feel better about giving up the extra Bonus Action attack from Martial Arts/Flurry of Blows, and that's less important on a multiclass character.
  2. One with the Blade, Path of the Kensei (3 weapons): By this level you should have ample access to magic weapons either via permanent magic items or spells like Magic Weapon. Adding a 3rd Kensei Weapon is probably useless.
Way of the Long Death

If you want temporary hit points, there are better options than Touch of Death. Hour of Reaping is really good, but it's not worth 6 levels on its own so you'll do best if you were primarily here for other monk features.

  1. Touch of Death: Neat, but depends on your class level. It's not totally worthless if you go no further into monk, but I wouldn't take 3 levels just to get this.
  2. Hour of Reaping: An absolutely stellar crowd control effect if you have the wisdom to back it up. Potentially very useful for classes with strictly limited resources between rests. But
Way of the Open Hand

Way of the Open Hand is great for single-class monks, but for multiclass characters it's just not a good option since you won't have the abundance of Ki to make Open Hand Technique a meaningful part of your tactical options.

  1. Open Hand Technique: While this is a great option for a monk with abundant Ki, multiclassing makes it a difficult prospect.
  2. Wholeness of Body: Absolutely not worth 6 levels.
Way of Shadow

Way of Shadow is a tempting option for characters built for stealth, especially if you don't have Darkvision already.

  1. Shadow Arts: While you don't have much Ki to work with, many of the listed spells have long durations so you can get a lot out of your limited pool of Ki.
  2. Shadow Step: Shadows and dim light are abundant almost everywhere except outside during the day, and the fact that you can use this without a usage limitation means that it can be a go-to tactical option. Rogues will find this especiall appealing as an easy way to get Advantage in order to deliver Sneak Attack.
Way of the Sun Soul

Sun Soul adds a little bit of the Light Domain Cleric to the Monk. If you want to be a cleric, go take a level of cleric instead.

  1. Radiant Sun Bolt: Take a level of cleric and learn Sacred Flame.
  2. Searing Arc Strike: This already isn't a fantastic ability, and the fact that you'll have comparably poor Ki just makes it worse.

Paladin

The Paladin has a lot to offer other Charisma-based classes like the Sorcerer and the Warlock. The Paladin's excellent durability and offensive martial capabilities are great, especially with a bigger pool of spell slots behind it.

  1. Divine Sense, Lay on Hands: Divine Sense is very situational, and Lay on Hands is heavily dependent on class level. You can use it to remove diseases/poisons, but doing so costs an entire class level worth of points so you're not going to do it often. The Paladin's initial proficiencies are comparable to the Fighters, but unless you plan to take a second level of paladin the Fighter is typically a better choice.
  2. Divine Smite, Fighting Style, Spellcasting: Two levels of paladin can turn the Sorcerer and the Warlock into serious martial threats. Divine Smite with an abundant pool of spell slots behind it is a terrifying pile of damage output, especially if you can score critical hits with some frequency. Fighting Style is great on any character, especially martial ones, and the Paladin's spellcasting includes several excellent options even among the 1st-level spells.
  3. Divine Health, Sacred Oath: Divine Health is situationally useful. The benefits of your Sacred Oath vary, but since every oath gets Channel Divinity at this level, you're getting a powerful ability that you can use once per Short or Long Rest.
  4. Ability Score Increase: Every class gets an Ability Score Increase at 4th level, and if you already took three levels in the class it's often very tempting to take one more just to get the ASI.
  5. Extra Attack: Standard for most martial classes, and an essential boost to most martial characters' damage output.
  6. Aura of Protection: Possibly the best buff to saving throws in the game. If you have the Charisma to back it up, you're suddenly much more durable.
Oath of Conquest

None of this will really define your build, but this is a good set of options for a Sorcadin.

  1. Channel Divinity: Conquering Presence amd Guided Strike, Oath Spells: Guided Strike is a great option if you're using Great Weapon Master or Sharpshooter. Conquering presence is decent crowd control. The new spells also include Armor of Agathys, which is spectacular on front-line martial characters.
Oath of Devotion

Sacred Weapon is a very tempting option for both Sorcadins and Hexadins. Adding your Charisma to your attack rolls (especially if you're a Hexadin and you already do that) is a significant mathematical improvement to your damage output.

If you have feats like Great Weapon Master or Sharpshooter, Sacred Weapon will offset much of the attack penalty and significantly increase your expected damage output, allowing you to perform 1-minute surges of incredible weapon damage output.

  1. Channel Divinity: Sacred Weapon and Turn the Unholy, Oath Spells: Sacred Weapon is a huge mathematical boost to your attack rolls. Remember that Advantage is worth roughly +3.25 on attacks, so if you have a +3 Charimsa modifier or better you're getting roughly the same thing. Plus, unlike Oath of Vengeance's Vow of Enmity, the attack bonus applies to everything you attack rather than to a single target. Plus, you can add Advantage on top of that to make it nearly impossible for you to miss. Turn the Unholy is fine for handling groups of fiends and undead. However, you need the Charisma to make it viable so it's not as easy for multiclass characters to use as Oath of Vengence's Vow of Enmity.
Oath of Glory

A solid option for most Strength-based martial builds, especially if you like to Grapple or Shove.

  1. Channel Divinity: Peerless Athlete and Inspiring Smite, Oath Spells: Heroism is a good buff, especially if you can reliably pass the saves to maintain Concentration. Peerless Athlete is great for characters that like to Grapple or Shove. Rage is easier if all that you want is occasional help help with Stength (Athletics), but Rage is also limited to a number of rages per Long Rest which scales very slowly, while Channel Divinity works twice per Short Rest, so there's room to say that this is better. Inspiring Smite is dependent on class level, but the base of 2d8 is very generous already, especially if you put it all on a single creature.
Oath of Redemption

Emissary of Peace is great for face characters, and Rebuke the violent is a great combat option. Overall a good option, but not so great that it will define your build.

  1. Channel Divinity: Emissary of Peace and Rebuke the Violent, Oath Spells: Emissary of Peace provides a significant bonus to Charisma (Persuasion), which is a rare non-combat use of Channel Divinity. Rebuke the Violent is a great way to respond to enemy critical hits. Neither option is level-dependent.
Oath of the Ancients

If you want nature-based crowd control, try some druid levels.

  1. Channel Divinity: Natures Wrath and Turn the Faithless, Oath Spells: Nature's Wrath is a decent single-target crowd control option, and Turn the Faithless is good for crowds of the affected creature types, but Nature's Wrath allows repeated saves and Turn the Faithless works on foes which aren't abundant in most campaigns. Between the two abilities you don't jabe an easy go-to option in any given encounter, so you may go long stretches where you get little or not benefit from having this ability.
Oath of the Crown

Nothing new here which couldn't be found elsewhere in a better form.

  1. Channel Divinity: Champion Challenge and Turn the Tide, Oath Spells: Champion Challenge is great, but redundant with Compelled Duel which is already on the Paladin's spell list. Turn the Tide is basically Mass Healing Word, but it only affects creatures than hear you and if you want healing like that you can get better options form the Cleric and the Druid.
Oath of Vengeance

Vow of Enmity is why you're here, and while it's great you can get easy Advantage from Reckless Attack, and Oath of Devotion's Sacred Weapon is more mathematically effective you're increasing your Charisma. This isn't a bad option, there are just better options with similar effects.

  1. Channel Divinity: Abjure Enemy and Vow of Enmity: Abjure Enemy is hard to use since it's easy to resist and many of the best targets for it will be immune to it since immunity to fear is common among fiends and undead. But Oath of Enmity is pretty good since you can use it against anything.
Oathbreaker

If you want to control undead, you're probably either a Cleric or a School of Necromancy Wizard. In either case, you can rely on spells instead of Channel Divinity both for handling undead and for making enemies Frightened. These are fine options for the Paladin, but for a multiclass dip they're hard to justify.

  1. Channel Divinity: Control Undead amd Dreadful Aspect, Oath Spells: The spells aren't great for a typical paladin, but they're more useful if you have full spellcasting. Control Undead is nice, but full spellcasters can typically do the same thing more effectively. Dreadful Aspect is decent crowd control, but again spellcasters can do the same thing much better.

Ranger

A single level in the Ranger gets you the same proficiencies as multiclassing into the Fighter, plus an additional skill proficiency. But that's generally not what people multiclass into the Ranger for. Generally if you're taking ranger levels you're going 2 levels for Fighting Style and Spellcasting or three levels for a subclass. However, you can get similar benefits from other classes like the Fighter or the Rogue, so the Ranger is rarely a go-to multiclass option.

  1. Fighting Style, Spellcasting: Fighting Style is always welcome, but most of the Ranger's low-level spellcasting isn't great. Hunter's Mark is interesting, especially for builds which make numerous attacks, but there are few other remarkable options.
  2. Primeval Awareness, Ranger Archetype: Primeval Awareness is hard to use. The benefits of your ranger archetype will vary.
  3. Ability Score Increase: Every class gets an Ability Score Increase at 4th level, and if you already took three levels in the class it's often very tempting to take one more just to get the ASI.
  4. Extra Attack: Standard for most martial classes, and an essential boost to most martial characters' damage output.
Beastmaster

The Beastmaster is already a bad archetype, and your companion's hit points depend on your class level so multiclassing into Beastmaster is a profoundly poor choice.

  1. Ranger's Companion: Bad and too dependent on ranger class level.
Gloom Stalker

Fantastic for any character planning to spend a great deal of time fighting in the dark or in places where artificial light is necessary.

  1. Gloom Stalker Magic, Dread Ambusher, Umbral Sight: This is a truly stellar level. Dread Ambusher is great for any martial character, but Umbral Sight is just absolutely incomparable. If your party is fine with working in the dark (warlocks with Devil's Sight are your friend), Umbral Sight is a massive tactical advantage. Even if your party can't manage to fight in darkness, you can still hide just outside of the range of light sources and fight from afar very effectively.
Horizon walker

Nothing that you need to have. Planar Warrior is probably why you're here, but if you just want extra damage Hunter with Colossus Slayer adds just as much damage without eating your Bonus Action.

  1. Horizon Walker Magic, Detect Portal, Planar Warrior (1d8): Detect Portal is very situational. Planar Warrior's damage isn't much better than Hunter's Mark, but converting your damage to force damage makes it nearly impossible to resist which may be appealing.
Hunter

Hunter's Prey offers options which work for a variety of builds and in several different scenarios, so it's a good option for nearly any martial character.

  1. Hunter's Prey: Enough options that almost any martial build will benefit, and the effects never scale so you get everything you need at 3rd level.
Monster Slayer

Nothing truly stunning here, but it's a solid set of options for an ambush predator like a ranger/rogue multiclass build.

  1. Monster Slayer Magic, Hunter’s Sense, Slayer’s Prey: Hunter's Sense is neat, but you'll need to sneak up on the creature if you don't want to spend an Action in combat staring at it. Slayer's Prey is basically Hunter's Mark for free once per Short Rest, and they stack. If you are very stealthy and very good at sneaking up on enemies, you can give yourself a huge advantage before combat starts.

Rogue

The Rogue's first three levels are fantastic for a number of reasons. Rogues get more skill/tool proficiencies at 1st level than any other class, and Expertise on top of that benefits a wide range of characters. Sneak Attack is dependent on class level, which makes it hard for multiclass characters, but no one is going to complain about a few extra d6's of damage every turn even though it's not as much as a single-class rogue might get.

  1. Expertise, Sneak Attack, Thieves' Cant: Even though multiclassing into rogue only gets you one proficiency, you still get Expertise in two things. Sneak Attack can be hard since it's so dependent on scaling with class level, but even without a ton of Sneak Attack damage a few dice can still be a notable addition to your damage output. Thieve's Cant is neat but rarely important.
  2. Cunning Action: Versatile and reliable, many other classes can benefit from the tactical options offered by Cunning Action.
  3. Rogueish Archetype: Varies.
  4. Ability Score Increase: Every class gets an Ability Score Increase at 4th level, and if you already took three levels in the class it's often very tempting to take one more just to get the ASI.
  5. Uncanny Dodge: Useful on literally any character, this can protect you from from a huge amount of damage over your character's career.
  6. Expertise: You probably already covered your favorite proficiencies, but more Expertise is never bad.
Arcane Trickster

If you just want wizard spellcasting, there are much better options elsewhere.

  1. Mage Hand Legerdemain, Spellcasting: Mage Hand Legerdemain is neat, but not very impactful for multiclassing. The spellcasting is basically just worse wizard spellcasting so generally if that's what you want you'll do better with a level of Arcana Domain Cleric or Wizard.
Assassin

Perfect for any ambush predator build. Pile on things like the Bugbear's Surprise Attack, spells like Hunter's Mark, effects like Divine Smite or Eldritch Smite, Brutal Critical. Whatever you've got that makes for big critical hits.

  1. Bonus Proficiencies, Assassinate: The additional proficiencies are nice, but they're not why you're here. Assassinate is a great tactical option even without a lot of Sneak Attack damage. If you have additional abilities like the Barbarian's Brutal Critical, the Paladin's Divine Smite, or the Warlock's Eldritch Smite you can use Assassinate to start damage with a huge pile of damage.
Inquisitive

Not a great choice for multiclass builds.

  1. Ear for Deceit, Eye for Detail, Insightful Fighting: Ear for Deceit and Eye for Detail are only situationally useful, and Insightful Fighting is only meaningful if you have a lot of Sneak Attack damage, which you won't because you're multiclassing.
Mastermind

There are better ways to get all of the benefits of the Mastermind.

  1. Master of Intrigue, Master of Tactics: Master of Tactics is neat, but if your party just needs someone to provide the Help action in combat a familiar will suffice. Master of Intrigue is fun for a campaign that's heavy on roleplaying, but if you just want more tool proficiencies you can get them more easily from your background or from feats.
Scout

Mechanically interesting for ranged combat builds, and thematically interesting for ranger/rogue multiclass builds.

  1. Skirmisher, Survivalist: Skirmisher is a good option for ranged combatants of all kinds. Survivalist is Expertise in two more skills, which is always welcome even if Survival is only rarely useful.
Swashbuckler

A great option for any melee build.

  1. Fancy Footwork, Rakish Audacity: Fancy Footwork is the ultimate hit-and-run ability, and Rakish Audacity makes Sneak Attack an easy option for any melee build, not to mention the bonus to Initiative. This is a great level for any melee build.
Thief

Fast Hands is neat, but it's hard to use.

  1. Fast Hands: The primary appeal of Fast Hands is the ability to use items as a Bonus Action. Unfortunately, the list of items which work with Fast Hands is short so if you go this route you need to really know what you're doing with it.

Sorcerer

The Sorcerer's spellcasting offers a lot of great options for multiclass characters. Not only do you get more cantrips than most classes and access to several fantastic 1st-level options, but as you gain level Font of Magic and Metamagic offer a ton of utility to any spellcaster.

  1. Spellcasting, Sorcerous Origin: Sorcerer spellcasting is fine, and includes a lot of staple defensive options like Absorb Elements and Shield, both of which are 1st-level spells that work at any character level so if you're not going far into Sorcerer you'll still get quite a bit from one level of spellcasting. Sorcerers also get more cantrips than most spellcasters, including great multiclass options like Green-Flame Blade, and they get their subclass at first level so you have a lot of flexibility even with a 1-level class dip.
  2. Font of Magic: Font of Magic is great, and it works for any class that depends on casting spells. Font of Magic doesn't care where the spell slots come from, so even if you're feeding it Pact Magic spell slots, you can still generate Sorcery Points. However, I haven't seen confirmation that you can use Sorcery Points to generate Pact Magic spell slots, so I think that's not allowed.
  3. Metamagic: Metamagic is one of the best reasons to multiclass into the Sorcerer. Even warlocks can benefit significantly, especially if you use your sorcerer spell slots for nothing but sorcery points.
  4. Ability Score Increase: Every class gets an Ability Score Increase at 4th level, and if you already took three levels in the class it's often very tempting to take one more just to get the ASI.
  5. Sorcerous Origin Feature: Varies.
Divine Soul

Want access to the cleric spell list and the sorcer spell list at the same time? This is how you get it. Favored of the Gods is just an incredible bonus on top of the already exceptionally good spellcasting benefits.

  1. Divine Magic, Favored by the Gods: Divine Magic offers access to the cleric spell list, meaning that you can get options like Guidance and Booming Blade in the same place. Staple options like Bless are great addition to the Sorcerer's already great spell list. There are enough good options here that don't rely on your spellcasting ability that you can easy use up all of your limited spells known without touching Charisma even once. Favored of the Gods is a a great backup option for import saving throws, and it's useful on literally any character.
Draconic Bloodline
  1. Dragon Ancestor, Draconic Resilience: 13+Dex AC. The AC will exceed any light armor without spending a spell slot on Mage Armor. You also get one extra hit point per sorcerer level, putting your hit points in line with classes with d8 hit points, which can help for melee builds dipping into sorcerer.
  2. Elemental Affinity: If you're building a blaster, this can be a huge damage boost. You can also spend a Sorcery Point to get damage resistance based on your Dragon Ancestor for an hour, which is a great trade.
Shadow Magic

Everything that Shadow Magic grants is great, and aside from Hound of Ill Omen you don't even need to be primarily a spellcaster to enjoy the benefits.

  1. Eyes of the Dark, Strength of the Grave: A great way to get permanent Darkvision if your race doesn't already get it. Strength of the Grave is neat and might save your life, but it's unreliable unless you're good at Charisma saving throws.
  2. Eyes of the Dark (darkness): Most sorcerers don't get another feature at third leve. Eyes of the Dark allows you to create an area of darkness which you can see in, but no one else can (short of warlocks with Devil's Sight and creatures with similar abilities). It's similar in many ways to Shadow of Moil.
  3. Hound of Ill Omen: Spectacular for any spellcaster, especially if you like save-or-suck spells.
Storm Sorcery

Tempestuous Magic is great for spellcasters afraid to be dragged into melee, but that's really the only thing of interest here so you won't feel bad about stopping short of 6th level.

  1. Wind Speaker, Tempestuous Magic: Tempestuous magic allows you to quickly and safely move out of melee range, which is tempting for many spellcasters. Wind Speaker is neat, but only situationally useful.
  2. Heart of the Storm, Storm Guide: Heart of the Storm is dependent on class level, and Storm Guide is almost entirely for flavor.
Wild Magic

Tides of Chaos can be very powerful, but introducing Wild Magic to your game can quickly turn a sensible, enjoyable game into a crazy, unpredictable game where fireballs suddenly go off while your eating lunch in town.

  1. Tides of Chaos, Wild Magic Surge: Wild Magic Surge is the go-to way to add bits of randomness and chaos to your game. But Wild Magic Surge only occurs if you cast a sorcerer spell. Conversely, Tides of Chaos allows you to give yourself Advantage at least once per day whenever you need it, which is hard to pass up. Your DM can throw a Wild Magic Surge at you any time after that to reset Tides of Chaos, so if you signed up for some extra chaos your DM gets to throw it at you whenever they want.
  2. Bend Luck: Expensive, but very powerful. Unfortunately you'll have a small pool of Sorcery Points so it may be hard to spend the Sorcery Points to power this.

Warlock

A spectacular class dip for any martial character that can feasibly be built around Charisma. Pact Magic is difficult to combine with regular Spellcasting, but it's not impossible to do, and the fact that Pact Magic stops advancing at 10th level makes multiclassing a tantalizing option for warlocks.

  1. Otherworldly Patron, Pact Magic: One Warlock spell slot, even though it recharges on a Short or Long Rest, is not going to be impactful. Unless you plan to take more warlock levels, you're likely here for the Otherworldly Patron features.
  2. Eldritch Invocations (2): There are a number of excellent and diverse Eldritch Invocation options so it's easy to find something useful for nearly any character, and if you take more warlock levels you can retrain your invocations. You also get a second spell slot at this level, which is great if you've got features like Divinite Smite which you can use to turn spell slots into burst of damage.
  3. Pact Boon: The Pact Boon options have a lot to offer, and you can retrain one of your invocations to take advantage of your choice of Pact Boon. For example: If you took Pact of the Blade, you could retrain an Invocation into Improved Pact Weapon to get easy access to a magic weapon with a +1 attack/damage bonus.
  4. Ability Score Increase: Every class gets an Ability Score Increase at 4th level, and if you already took three levels in the class it's often very tempting to take one more just to get the ASI.
  5. Eldritch Invocation (1): You already have two invocations, and it's hard to think of builds where a third will add much. You can take something like Thirsting Blade to effectively replace Extra Attack, but I'm not sure if that's a great option on a multiclass character.
  6. Otherworldly Patron Feature: Varies.
The Archfey

The Archfey is a hard choice for multiclassing. Adding Faerie Fire to your warlock spell list may be the best you can get from a class dip into the Archfey.

  1. Fey Presence: An interesting option for melee builds since you'll often have enemies in melee with you, but the 10-foot cube AOE raises some annoying mechanical questions since it covers at most half of each 5-foot space adjacent to you. The short duration doesn't help either.
  2. Misty Escape: A great way to get out of melee in a hurry, and it's not dependent on class level or Charisma or anything.
The Celestial

Other classes offer similar but more effective options.

  1. Expanded Spell List, Bonus Cantrips, Healing Light: There's little reason to consider this over levels in the Cleric or Divine Soul Sorcerer. Healing Light is too dependent on class level, and the tiny number of cleric spells aren't meaningful enough to justify this over other subclass options.
  2. Radiant Soul: Neat, but not worth 6 levels.
The Fiend

The Fiend's features are great, but the spellcasting won't add much since much of it is AOE damage that's intended to benefit from your increasing spell slot level.

  1. Dark One's Blessing: Dungeons and Dragons is a game that involves a lot of reducing enemies to 0 hit points, so for the vast majority of characters this offers an easy way to get temporary hit points, especially on high-damage characters.
  2. Dark One's Own Luck: d10 is an average roll of 5.5, which is a massive bonus in 5e. This can easily turn a failed save into a successful one. But if you're here for this, consider levels in bard instead for Bardic Inspiration.
The Great Old One

The Great Old One is primarily about spellcasting, so multiclassing doesn't make this a good choice.

  1. Awakened Mind: Great for a Face character or for characters hoping to avoid notice while communicating, but I don't think it's good enough to multiclass to get it.
  2. Entropic Ward: Great for front-line martial builds, especially if you benefit a lot from Advantage like rogues do. But it only works once per Short or Long Rest so it's not a tactical option which you can rely on constantly.
The Hexblade

So effective that it single-handedly reset the character optimization meta. A 1-level dip into Hexblade can dramatically improve bards, paladins, and potentially even sorcerers.

  1. Expanded Spell List, Hexblade’s Curse, Hex Warrior: Hexblade's Curse works based on your Proficiency Bonus, so it remains effective and powerful at any character level. Hex Warrior gives you medium armor, shields, martial weapons, and you can use one weapon to fight with your Charisma modifier in place of Strength or Dexterity, solving the MAD problem for bards, paladins, and sorcerers who want to fight with weapons.
  2. Accursed Specter: Nowhere near good enough to even consider 6 levels.
The Undying

Almost nothing worth having, and what little there is can be found elsewhere. Consider the Grave Domain Cleric instead.

  1. Expanded Spell List, Among the Dead: If you're worried about undead, take cleric levels.
  2. Defy Death: There are number of better and lower-level class features which will protect you from falling to zero hit points, but even in the absence of those features this isn't good enough to justify six levels.

Wizard

Wizards have numerous "dead levels" where they get nothing except a new spell level. While that's fine for single-class wizards, it's not great for multiclassed characters. Typically you'll go no further than 2nd level once you get the initial subclass features.

  1. Arcane Recovery, Spellcasting: Wizard spellcasting is really good, and includes ritual casting and a ton of 1st-level rituals including crucial options like Detect Magic. Arcane Recovery is very level-dependent, so you're unlikely to get anything beyond an extra 1st-level spell slot.
  2. Arcane Tradition: Varies.
Bladesinging

For the Arcane Trickster Rogue, the Artificer, and the Eldritch Knight, Bladesong is a tempting prize. Unfortunately it's not useful for other classes since nearly all characters dump Intelligence.

  1. Training in War and Song, Bladesong: You're here for Bladesong. Pile Intelligence on top of all of your important martial combat stats, and add it to your saves for Concentration so that you can maintain other powerful buffs.
Chronurgy Magic

Not actually bad, but School of Divination is better.

  1. Chronal Shift, Temporal Awareness: Chronal Shift is a less-reliable version of School of Divination's Portent. Temporarl Awarness is great for the Wizard, but other classes either won't haveenough Intelligence to make it useful or they'll go for Bladesignging.
Graviturgy Magic

Being able to replace the only ability with a spell is a good indicationg that this isn't a good multiclass option.

  1. Adjust Density: Tempting you have an ally who likes to Grapple or Shove, but you could also cast Enlarge/Reduce and take a better subclass.
School of Abjuration

Too dependent on class level and wizard spells.

  1. Arcane Ward: This is a great ability but it's totally dependent on both your class level and on casting wizard spells, both of which are difficult prospects for a multiclassed character. You'll likely never get more than 7 hit points in the ward, and casting 1st-level spells will only add 2 to the ward. Probably your best choice is to to turn all of your spell slots into Shield and Absorb Elements, but that's a very unsatistying use of the feature, especially since you get just 2 hp each time.
School of Conjuration

Not worth the levels.

  1. Minor Conjuration: This is a great ability, but it's not worth multiclassing into wizard just to get it.
School of Divination

Literally always good.

  1. Portent: This is a spectacular ability on any character.
School of Enchantment

Hard to use, but maybe effective on a close-range caster build?

  1. Hypnotic Gaze: This is hard for many characters to use because you need to get within 5 ft. of the target and spend successize Actions to hold the target's gaze, effectively trading your own Action to negate the target's ability to act. That can be useful in some situations, but it's a dangerous gamble if you're not built for melee and you try to use this in combat. With the exception of Eldritch Knights and Arcane Tricksters, I don't see much use for this for other classes.
School of Evocation

The Sorcerer and the Wizard generally make the best Blasters, and the Sorcerer gets comparable metamagic. Maybe the Artillerist Artificer could use this?

  1. Sculpt Spell: Helpful for blasters, but giving up two levels may be hard compared to advancing your class two more levels and getting higher-level spells is usually more effective.
School of Illusion

The only possible use case I can think of is the Arcane Trickster if you want more wizard spellcasting, but if that's what you're doing there are better subclass options for you. Bladesinging and School of Enchantment may both be better.

  1. Improved Minor Illusion: 2 levels to be a little better at one cantrip. Not worth it.
School of Necromancy

Tempting for a high-damage offensive spellcaster, but not defining or essential in any build.

  1. Grim Harvest: This is tempting becuase it applies to non-wizard spells, so if you're using offensive spells from another class this can be a good way to keep your hit points up. Giving up access to higher-level spells to get this may be a hard trade, but if you're getting by on staple options like Fireball and Spirit Guardians which scale well with spell level you can get a lot out of this.
School of Transmutation

Nothing worth the levels.

  1. Minor Alchemy: Very versatile, but it's not powerful enough to justify multiclassing.
War Magic

This is objectively fantastic, but it's hard to find a build that will want it. The obvious answers are the Arcane Trickster Rogue, the Battlesmith Artificer, and the Eldritch Knight Figher. But those are the exact same characters that line up well for Bladesinging, and Bladesinging tends to get more attention.

But there are still some standout builds where War Magic shines. Bladesinging is only available to elves (and half-elves since they count as elves and humans at the same time), and it only works for one minute bursts, after which if you're not also a good spellcaster you're pretty useless. By comparison, War Magic works as long as you have your Reaction so you can negate attacks and shug off saving throws all day long. The bonuses won't be as big as those from Bladesong once your Intelligence hits +5, but the fact that you can use them constantly may be worthwhile. Bladesinging also doesn't give you an Initiative bonus.

  1. Arcane Deflection, Tactical Wit: +2 AC as a Reaction isn't quite as good as Shield, but it's still really good. +4 to a saving throw as a Reaction is absolutely unbelievable. Sure, you can't cast non-cantrips on your next turn, but for many multiclass characters that doesn't matter even slightly. Tactical Wit is a great Initiative bonus, too.

Example Multiclass Builds

All the stuff above was... well, it was a lot. I get it. Character optimization can be complicated, and those complications increase exponentially when you bring multiclassing into the equation. This section details several examples of multiclass options which appeal to specific classes. So if you already know the class that you want to focus on (your "primary class") but want to explore multiclassing, this section offers several go-to multiclass options for each class which you can pick up without a ton of trouble and without adding a lot of complication to your build.

Artificer

Fighter (Any) 1 / Artificer (Any) X: Starting with a level in fighter gets you heavy armor without giving up proficiency in Constitution saves. For artificer subclasses which don't already get heavy armor proficiency, this can be a significant boost to your AC and can reduce the need for Dexterity so that you can focus on other ability scores. However, if you don't meet the Strength requirement you'll face a persistent and annoying speed penalty.

Rogue (Thief) 3 / Artificer (Any) X: Do you like items? Of course you do! On top of Expertise, three levels in rogue (thief) can get you Fast Hands, allowing you to take the Use an Object action as a Bonus Action.

Wizard (Bladesinging) 2 / Artificer (Battlesmith) X: Bladesong is a fantastic buff for an Intelligence-based character, and the Battlesmith is an Intelligence-based front-line character so the combination is pretty obvious. Between Battle Ready and Bladesong you're adding Intelligence to many of your most important stats so you can focus on Intelligence almost exclusively. However, Bladesong only works twice between each Short or Long Rest, and the Adventuring Day rules suggest two Short Rests in a day of roughly 10 encounters, so you'll find that roughly one in three encounters will require you to go without using bladesong. Make sure that you can still function during those encounters.

Barbarian

Fighter (Champion) 3 / Barbarian (Any) X: Improved Critical synergizes with Brutal Critical very well. Add in the Half-Orc's Savage Attacks and grab a greataxe, and your critical hits will be frequent and devastating. With Reckless Attack and Improved Critical, your odds of rolling a critical hit are 19% (nearly 1 in 5).

Rogue (Assassin) 3 / Barbarian (Any) X: Similar to the Fighter (Champion) above, the Assassin's Assassinate feature synergizes with Brutal Critical very well. However, you trade the Champion's sustainably high critical hit output for guaranteed critical hits the first round of combat, provided that there are enemies who haven't acted before you. If you go this route, don't neglect your Dexterity and look for other ways to improve your Initiative rolls.

Bard

Sorcerer (Any) 1, 2, or 3 / Bard (Any) X: Sorcerers get proficiency in Constitution saving throws (crucial for Concentration) and get melee cantrips like Booming Blade which aren't normally available to the Bard without spending powerful resources like Magical Secrets. The overlap in spellcasting ability means that the spells gained from sorcerer levels will remain effective as you advance. Two levels gets you Font of Magic which doesn't care where the spell slots come from, and three levels gets you Metamagic which similarly doesn't care whether you're casting sorcerer spells or not.

Warlock (Hexblade) 1, 2, or 3 / Bard (Any) X: Hexblade significantly simplifies a lot of the Bard's deficiencies in melee combat. Acces to medium armor and shields removes the need to pursue College of Valor, and cantrips like Booming Blade will close the damage gap between single attacks and Extra Attack. Get 14 Dexterity, a suit of half plate, and a shield and you'll have 19 AC and you can focus on your Charisma and improve both your martial capabilities and your spellcasting at the same time. A second Warlock Level gets you invocations, and a third can get you both Pact of the Blade and Improved Pact Weapon. However, that second or third level mean trading some spellcasting for more martial capabilities, so you need to decide what balance you want to strike with your character.

Wizard (School of Divination or Chronurgy Magic) 2 / Bard (College of Eloquence) X: Sieze control of the outcome of rolls! Wizard offers access to either Portent or Chronal Shift depending on which of the two schools you pick, allowing you to change the outcome of two rolls per days.

The remainder of your levels go into bard primarily for Bardic Inspiration. Your number of uses of Bardic Inspiration are Charisma-based, so you want this to be a high-Charisma build and limit your wizard spells to spells which don't depend on your spellcasting modifier (absorb elements, shield, and utility options are all good choices).

To go even further, add Halfling for the Lucky racial trait, and consider the Bountiful Luck feat. You can add the Lucky feat regardless of your race, too. However, that's two feats which puts off Ability Score Increases for a long time, and between that and being a full spell level behind on your bard spellcasting you'll need to avoid offensive spells and spells which depend on your spellcasting ability modifier as much as possible.

You can add a level of Wild Magic Sorcerer to gain Tides of Chaos, but that only applies to yourself and adding a third class adds a lot of complexity to your character (especially your spell list) for little benefit.

Cleric

Fighter 1 or 2 / Cleric (Any) X: Starting with Fighter gets you proficiency in Constitution saves, which is a huge help with Concentration checks. It also gets you heavy armor if your domain doesn't provide it and a Fighting Style. Two levels gets you Action Surge, allowing you to do things like casting two spells in the same turn without running into the limitation on Bonus Action spells. Action Surge only works once per Short or Long Rest, but it's still noteworthy. You might go to three levels for a subclass, but that's uncommon.

Monk (Any) 1 / Cleric (Any) X: Unarmored Defense and Martial Arts are interesting options for clerics that don't get heavy armor proficiency. Grab a monk weapon and focus on Dexterity and Wisdom, and many domains which offer a version of Divine Strike can be considerably more effective in melee. The second attack from Martial Arts will be redundant for War Domain, but other domains like Grave Domain or Light Domain gain a reliable way to make more than one weapon attack per turn. Unarmored Defense also allows you to hit 20 AC (though this requires quite a few Ability Score Increases) without using armor or a shield, which means that you can keep a hand free to perform spellcasting components without reluing on War Caster or juggling your weapon.

Paladin (Any) 2, 5, or 6 / Cleric (Any) X: Two levels of paladin offers Divine Smite, which combined with the cleric's better spell progression (and therefore larger pool of spell slots) offers more smites and generally better martial options for the Cleric. You won't get proficiency with Constitution saves like you would with a Fighter class dip, but If you can manage 6 levels Aura of Protection can help compensate or you can take Resilient. Unfortunately, this build can be very MAD since paladins are already MAD and you're adding a Wisdom requirement. Most likely, you'll have better results attempting the same build with a Divine Soul Sorcerer.

Rogue (Any) 1, 2, or 3 / Cleric (Trickery) X: The Trickery cleric makes sense in a stealthy party, but lacks the core proficiencies brought by a rogue, and doesn't have access to finesse weapons better than a dagger. If you want to replace a rogue with a trickery cleric, starting with a level of rogue gets you all of the rogue's proficiencies and a splash of Sneak Attack damage. Two levels gets you Cunning Action so you've always got a good use for your Bonus Action without pouring spell slots into Spiritual Weapon, and three levels gets you a bit more Sneak Attack and a subclass. Personally I would go for Arcane Trickster for the spellcasting or Mastermind for Master of Tactics to complement the cleric's support capabilities.

Druid

Barbarian (Any) 1, 2, or 3 / Druid (Circle of the Moon) X: Rage and Unarmored Defense are both appealing for Circle of the Moon because they both work while in Wild Shape. Reckless Attack does, too, but it's a big gamble since Wild Shape provides such a small pool of hit points before you're knocked out of Wild Shape. And, while Unarmored Defense does work in Wild Shape it doesn't necessarily work very well. I go into the math in my Practical Guide to Wild Shape.

Monk (Any) 1, 2, or 3 / Druid (Circle of the Moon) X: Martial Arts works while using Wild Shape, as does the Monk's Unarmored Defense. So long as your Wisdom is sufficiently high, you can improve the AC of many forms, though not all of them. I go into the math in my Practical Guide to Wild Shape. And, while Martial Arts does work in Wild Shape you need to take the Attack action and make an attack an "unarmed strike". Animal's natural weapon attacks are not unarmed strikes, so they don't count. That means that you may be punching and kicking in favor of biting and clawing. 2 levels get you Ki and Unarmored Movement, both of which work in Wild Shape (and Unarmored Movements applies to your new form's movement speeds). 3 levels gets you a subclass, but by this point you're setting yourself really far behind on Wild Shape so the drawbacks are arguably offsetting the benefits of the class dip.

Monk (Any) 1 / Druid (Circle of Spores) X: I know, two monk/druid builds seems redundant, but this is a really great combo that I can't ignore. Circle of Spores is difficult to optimize and it has a bunch of mechanical challenges. Druids have terrible AC and bad martial options, and while Symbiotic Entity helps compensate for both there's a ton of room for improvement. Unarmored Defense is a great option for the Circle of Spores Druid. Max out Dexterity and Wisdom and you can hit 20 AC without spells (that will obviously take a while). You can use Dexterity to fight with either a spear or a staff, removing the need for Shillelagh which is typically difficult for spores druids to forgo. Martial Arts offers an additional attack, allowing you to apply your bonus poison damage more frequently on top of the extra damage output from making twice as many attacks as a druid normally can. You don't need to go further into the Monk than level 1, which makes this an exceptionally powerful class dip.

Fighter

Barbarian (Any) 1, 2, or 3 / Fighter (Any) X: Rage is a really tempting buff, but it only works if you're not in heavy armor. Unarmored Defense is similarly great, but maxing out the AC requires a ton of Ability Score Increases. The Fighter gets more Ability Score Increases than any other class, which presents an opportunity to get your Strength, Dexterity, and Constitution all up to 20 for an AC of 20 totally naked. If you start with 16 Strength, 14 Dexterity, and 16 Constitution you can hit 20 in each if you take only one level of barbarian then go straight fighter after that. But more likely you're exploring barbarian for more than just the ability to fight unarmored, in which case options like Reckless Attack are extremely appealing for fighters.

Rogue (Any) 2 / Fighter (Any) X: 2 levels of rogue gets you a lot of skills and Cunning Action, which provides a powerful usage for your Bonus Action on a class with very few built-in Bonus Action options. This combines well with the Polearm Master+Sentinel combo because if enemies manage to get adjacent to you you can use Cunning Action to Withdraw safely then force your enemies to charge into your reach again to get close enough to attack you.

Ranger 2 / Paladin 2 / Fighter (Champion) 10+: Do you like Fighting Style? Here's how you get 4 of them. It's neat, but it's a bad build.

Monk

Barbarian (Any) 1 or 2 / Monk (Any) X: The two version of Unarmored Defense don't stack, but if you're not reliant on Wisdom for save DCs or anything like that, the Barbarian's version of Unarmored Defense may actually be better than the Monk's. De-emphasizing Wisdom means that you can instead focus on Constitution, thereby raising the Monk's relatively poor hit points compared to more durable from-lint martial classes. Two levels gets you Reckless Attack, which is a hard gamble for the Monk with d8 hit dice and low AC (until you gain enough ability score increases to raise it), but Advantage on 3-4 attacks (Extra Attack and Flurry of Blows) can yield a lot of damage output if you use it as an occasional damage boost rather than running Reckless Attack constantly like many barbarians do.

Rogue (Any) 1 / Monk (Any) X: Starting with a level in rogue adds a bunch of additional skills to the Monk. Monks are typically somewhere between a fighter-equivalent and rogue-equivalent, but since they don't have the durability to replace a fighter they're typically filling the space normally filled by a rogue. Starting with a level in rogue offers better skills and expertise, and if you want to enjoy the 1d6 of Sneak Attack damage you can use a dagger or a short sword. I wouldn't go past level 1 since Uncanny Dodge is so redundant with the options provided by Ki.

Paladin

Sorcerer (Any) 1 or 2 / Paladin (Any) X: Similar to the Warlock, the Sorcerer offers additional spellcasting options to the Paladin, and the multiclass is popular enough that it's affextionately nicknamed the "Sorcadin". On top of the extra spell slots, sorcerers get access to great spells like Booming Blade which can be powerful assets for martial characters. Two levels gets you Font of Magic, which allows you to convert your spell slots into Sorcery Points and back, and it's a common tactic to turn your spell slots into a pile of 1st-level slots because 1st-level slots have the best conversion rate from spell slot to Divine Smite damage dice. Personally I like a Draconic Bloodline Sorcerer with a Dexterity-based build; you can still hit 20 AC thanks to Draconic Resilience and there's no additional tracking beyond the spells.

Warlock (Hexblade) 1, 2, or 3 / Paladin (Any) X: Warlock/Paladin builds have been popular since 5e's release. The promise of recharging spell slots on a Short Rest in conjunction with Divine Smite is hard to pass up. This combination was affectionately nicknamed the "Lockadin", but gave way immediately to the "Hexadin" the moment that Hexblades were published. The ability to use Charisma for attack and damage with weapons made the Paladin considerably less MAD, so they could emphasize both their martial capabilities and their magical abilities by increasing the same ability score. If you go this route, there are good break points at levels 1, 2, and 3. Level 2 gets a second spell slot and an invocation, and level 3 gets you 2nd-level spells for bigger smites and you get Pact Boon.

Barbarian (Any) 1, 2, or 3 / Paladin (Any) X: Rage won't work in heavy armor, so if you want Rage you'll need to manage medium armor which will make the Paladin even more MAD than they already are. Still, if you can manage it both Rage and Reckless Attack are great on the Paladin.

Ranger

Druid (Any) 1 / Ranger (Any) X: The Druid's spellcasting is very similar to the Ranger's, but they get cantrips and several 1st-level spell options like Healing Word which the Ranger doesn't. Grab Shillelagh and you can build a high-Wisdom ranger and still work great in melee. Of course, you'll need to give up metal armor so you'll still need high Dexterity, and you can get access to the spells you want by taking Magic Initiate.

Fighter (Any) 1 / Ranger (Any) X: If you want to build a Strength-based ranger, this is the way to do it. Starting with the Fighter gets you heavy armor, a Fighting Style, and proficiency in Constitution saves so that you can maintain Concentration more easily with spells like Hunter's Mark and Guardian of Nature. This one-level class dip shifts the Ranger from a Rogue-equivalent to a high-damage Fighter-equivalent, allowing you to easily stand on the fron lines to protect your allies. Since you get two Fighting Styles, consider making your second either Defense for the AC or Protection to keep your allies safe.

Rogue (Any) 1, 2, or 3 / Ranger (Any) X: Rogue dips have been a favorite for rangers since at least 3rd edition. While rangers attempt to walk a line between the Druid, the Fighter, and Rogue, they're typically filling the role in a party typically covered by the Rogue. Rogues get better skill/tool proficiencies at first level, not to mention Expertise, so starting with a single level offers a great deal of extra non-combat options. You give up medium armor, but most rangers stick to light armor anyway. Two levels gets you Cunning Action, which is great but may conflict with the Ranger's spellcasting or with two-weapon fighting. Three levels gets you a subclass, but none of them offer anything that adds a lot to the ranger. Cantrips from Arcane Trickster could be neat, though.

Rogue

Barbarian (Any) 2 / Rogue (Any) X: Reckless Attack is an easy source of Advantage, which is really convenient way for the Rogue to use Sneak Attack. It's high-risk, but fortunately you'll get Uncanny Dodge to help reduce some of the damage you would take. It's also easy to overlook Unarmored Defense for the Rogue, but it's a suprisignly great option. Rogues normally max out at 17 AC (short of spells and magic items) because light armor maxes out at 12+Dex. You can hit 12+Dex AC with the Barbarian's Unarmored Defense and 14 Constitution, which is easily achievable as early as first level. Rogues also get an extra Ability Score Increase, so hitting 20 Dexterity and 20 Constitution is not only possible, it's easy and it's probably a good idea. That gets you 20 AC totally unequipped.

Rogue (Any) 6 / Bard (College of Eloquence) 10 / ?: As much Expertise as possible! you get Expertise in 4 things from Rogue, and 4 things from Bard, and College of Eloquence lets you treat rolls of 9 or below on Charisma (Deception) and Charisma (Persuasion) as a 10, similar to the Rogue's Reliable Talent feature, but we can't get Reliable Talent without giving up the Bard's second round of Expertise of 10th level. Unfortunately, you may struggle with anything except skills.

Rogue (Any) 1 / Bard (Any) 2 / Rogue X: A more realistic version of the above build, you give up just 2 levels of rogue for an extra skill proficiency, Expertise in two more things, and the magnificent Jack of All Trades. You don't get to say "I have Expertise in 8 things", but you're actually a decent rogue which is probably more important. You'll want a bit of Charisma to fuel your limited spellcasting and Bardic Inspiration, but don't go crazy since your rogue levels are doing most of the work here.

Sorcerer

Fighter (Any) 1, 2, or 3 / Sorcerer (Any) X: Heavy armor and proficiency in Constitution saves. 2 levels gets you Action Surge, which makes Quicken Spell somewhat redundant so you can pursue other Metamagic options. Three levels gets you a subclass, which offers several interesting options. Personally I recommend the Eldritch Knight. You get a few more cantrips and some additional known spells, which is a big addition since the Sorcerer knows so few. However, since the spellcasting from Eldritch Knight is Intelligence-based, stick to spells which don't require spell attacks or saving throws, like Booming Blade, Absorb Elements, Shield, and other defensive or utility options.

Paladin (Any) 2, 5, or 6 / Sorcerer (Any) X: The "Sorcadin" build isn't always primarily a paladin. Just as the Sorcerer offers the Paladin aditional spellcasting, the Paladin offers the Sorcerer extra durability. If you want to be better with weapons, you might go all the way to 5th level in paladin for Extra Attack, or your might go to 6 for Aura of Protection. However, that's a lot of spellcasting to give up, and sorcerers get proficiency in Constitution saves so it's hard to give that up for heavy armor. The big gain here is Divine Smite which can pile on top of Booming Blade or Green-Flame Blade for big melee hits at a low spell slot cost. If you just want heavy armor, consider the Fighter Instead.

Warlock 2 or 3 / Sorcerer: Font of Magic doesn't care that warlock spell slots come from Pact Magic rather than from Spellcasting, and Eldritch Blast with Agonizing Blast is a powerful offensive option. 2 levels gets you Agonizing Blast and 2 spell slots, and three levels gets those spells slots up to level 2 so that they're worth more Sorcery Points.

Warlock

Sorcerer (Any) 3 / Warlock (Any) X: Quicken Spell is really tempting with Eldritch Blast. Casting it twice in a single turn is a huge pile of damage, especially if you already have Hex and/or Hexblade's Curse running.

Fighter (Any) 1 / Warlock (Any) X: Starting with a level of fighter gets you heavy armor and proficiency in Constitution saving throws, which are crucial for maintaining Concentration. This is probably most effective for the Hexblade, but it's a tempting option for any warlock. The additon of Fighting Style is also very helpful regardless of your choice of weaponry.

Wizard

Artificer (Any) 1, 2, or 3 / Wizard (Any) X: Artificers start with proficiency in Constitution saving throws, medium armor, and shields. That's a big increase in durability for any wizard. Bladesingers have especially good synergy with the Battlesmith, and the combination works so well that you can favor either side of the class split and still be very effective depending on whether you want more spellcasting or more Infused Items.

Fighter (Any) 1 or 2 / Wizard (Any) X: Similar to the Artificer, the Fighter offers heavy armor and shields. However, the better armor and Fighting Style come at the cost of a level of spellcasting so there's some cost/benefit analysis to be done.

Sorcerer (Any) 3 / Wizard (Any) X: All the versatility of Metamagic combined with the versatility of the Wizard's spellbook. You give up higher-level spells known, but you still get full spell slot advancement. If you dump Charisma (and you probably should) you can still use your sorcers spellcasting for utility spells and staple defensive options like Absorb Elements and Shield which remain effective at every level but normally present a tax on your limited number of prepared spells.