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 revolves around Acererak the Archlich's self-bouncing trigger, which allows you to endlessly recast the lich for a single black mana. Carnival of Souls plays a crucial role by turning every one of those entry triggers into the exact black mana needed to recast him while fueling your life total, a cost cleverly offset by Diamond Mare's continuous lifegain whenever you cast your black spell. Meanwhile, The Kenriths' Royal Funeral sits quietly in the background, utilizing the graveyard to reduce legendary spell costs and eventually turning your endless cycles into massive card draw.