Tablet of the Guilds triggers, causing you to gain 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 loop relies on casting Acererak the Archlich over and over, turning its self-bouncing entry trigger into an endless engine. Carnival of Souls turns each of those creature entries into a burst of black mana to pay for the lich while neutralizing the life loss using Tablet of the Guilds to gain life on cast. Meanwhile, Heliod, the Radiant Dawn // Heliod, the Warped Eclipse sits quietly on the board, offering its flash-granting static ability and cost reduction to let the whole loop churn smoothly through the dungeon.