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 clever loop turns Acererak the Archlich's self-bouncing nature into a perpetual motion machine by recasting him over and over for free. Every time you cast him, Carnival of Souls provides the black mana needed to pay his casting cost while Demon's Horn offsets the life loss, keeping your health stable as you replay the lich. Meanwhile, Temur Battlecrier sits quietly in the background, slashing Acererak's mana cost down to zero once you have enough big bodies on board to fuel the discount, allowing you to venture into the dungeon infinitely and reap endless rewards.