MCDM Productions released Beastheart and Monstrous Companions in late 2021, a PDF supplement which introduces a new class (The Beastheart) and a system for bringing Monstrous Companions into your game so that your party can have monsters like gelatinous cubes and hellhounds as pets or sidekicks.
The mechanics for Monstrous Companions are good. They’re fun, they’re satisfying, there’s enough crunch to sink your teeth into without it bogging down the game, and the companion options are mechanically distinct enough to be interesting without significant balance issues. MCDM did a really great job designing and balancing the system. They even have a sidebar about designing your own companions so we don’t have to clumsily reverse-engineer it yourself.
Perhaps my favorite part: MCDM found a way to make mounted combat work by providing mounts that aren’t made of paper, and which can work as independent mounts without making it impossible to fight effectively in melee.