Bontu's Monument triggers, causing you to gain life and each opponent to lose life.
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 drawback into a powerhouse by repeatedly recasting him for free. With both Bontu's Monument and Centaur Omenreader lowering his casting cost to zero, you don't even need outside mana once the engine is running. As Acererak bounces and re-enters, Carnival of Souls graciously provides the black mana to keep the cycle going while triggering Bontu's Monument to slowly drain your opponents down to zero life.