Cast Acererak either from your hand or from the command zone by paying plus commander tax, if applicable.
Diamond Mare 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 transforms Acererak the Archlich into a self-returning engine by leveraging Semblance Anvil to reduce his casting cost to zero, completely bypassing the need for traditional mana to recast him from your hand. As he repeatedly enters the battlefield, Carnival of Souls turns each of those entries into a generated black mana to offset his cost, while Diamond Mare conveniently counters the life loss and cushions your total life score. The beauty of this arrangement is that Acererak's entrance forces a dungeon venture that never completes its journey, allowing you to infinitely cycle through the Lost Mine of Phandelver to flood the board with resources, triggers, and treasures.