Acererak the Archlich is a mythic Legendary Creature — Zombie Wizard card from Magic Online Promos (PRM), collector number 92688.
When Acererak enters, if you haven't completed Tomb of Annihilation, return Acererak to its owner's hand and venture into the dungeon. Whenever Acererak attacks, for each opponent, you create a 2/2 black Zombie creature token unless that player sacrifices a creature of their choice.