When Acererak enters, its first ability and Carnival of Souls trigger.
Resolve the Carnival of Souls trigger, causing you to add and lose 1 life.
Resolve the Acererak trigger, returning it from the battlefield to your hand, and venturing into Lost Mine of Phandelver.
Repeat.
This loop turns Acererak the Archlich's self-bouncing trigger into a perpetual engine for the Undercity by casting it for free, thanks to the cost reduction from Ezzaroot Channeler fueled by the lifegain from Prism Ring. As Acererak enters the battlefield, Carnival of Souls mitigates the life cost while generating the black mana needed to recast the Lich, creating a continuous loop of creature entries. By choosing to venture into *Lost Mine of Phandelver* rather than the Tomb of Annihilation, you bypass the completion restriction and repeat the entire sequence indefinitely for infinite dungeon progress and resources.