Reaper

Reaper is an undead Boneyard and Infinite enemy that grows stronger as the battle progresses. It opens each turn with a 3-hit spin attack, and whenever an ally is killed it teleports adjacent to the responsible unit, gaining +1 All Stats and +4 Health as vengeance. Reapers can walk through walls and leave no corpse on defeat. With multiple Reapers present, the deaths of their allies cascade into a string of teleports and buffs — prioritizing Reapers first, or using a durable tank to control who lands the killing blow, is essential.