Efreets 2 (Patreon)

The Cinderlord is another exploding punch-wizard, like the tanarukk, except unlike the tanarukk he actually is immune to fire. He can hit you with a curse that is mildly inconvenient in the moment (unless there's a red dragon around), but white-knuckle terrifying if you're still in the elemental plane of fire after the fight's over.

The Pyresinger casts a concentration-free flaming Bigby's Hand that can make it's own reactions twice a turn, filling the battlefield with little opportunity attack land mines and making him progressively more dangerous as the fight goes on. Pair this guy up with something that gives your players a compelling reason to move and you got yourself a stew going.