Aetherflux Reservoir 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.
By casting Acererak the Archlich over and over, you trigger a self-sustaining loop where its entry forces it right back to your hand while Carnival of Souls cushions the repeated mana cost with black mana and life loss. Meanwhile, Aetherflux Reservoir tracks every single repetition of this casting process to rapidly pump your life total sky-high, letting you safely convert that accumulated life into a lethal blast of 50 damage to finish off your opponents. Heliod, the Radiant Dawn // Heliod, the Warped Eclipse quietly anchors the strategy by letting you cast spells with flash and discounting their costs, ensuring your continuous dungeon delving through the Lost Mine of Phandelver runs smoothly and endlessly.