Looks like this Vengeance (Retribution?) Paladin procced something with lightning

DnD 5e – New Oath of Vengeance Paladin Handbook (Yes, Another!)

We’ve written several Paladin handbooks so far, largely with a Defender bent. Oath of Vengeance is arguably the strongest Striker option for the class, and this guide leans into the damage output while still maintaining some Defender capabilities with a combination of feats. Be an excellent battlefield controller against small numbers of enemies and woe betide anything you choose to focus your full ire on. Polearm Master makes a second appearance for the class and is even more core to it than it was for Oath of Glory.