Reaper

Reaper makes an appearance in Wizard. In the episode, he offers Finn and Jake the chance to earn magical powers for free, but the evil catch is that they must stop a comet. At the end of the episode, he offers them a Demon Heart. He may have been one of Bufo's minions. He is a Lich, which is an undead creature, usually associated with magic.

He also appears in Dungeon, where he challenges Jake to a duel.