Mortuary + Cauldron Familiar + Ashnod's Altar + Bolas's Citadel

Mortuary

Cauldron Familiar

Ashnod's Altar

Bolas's Citadel

How it works

1. Cast Cauldron Familiar either from your hand or from the top of your library by paying or 1 life respectively.
2. When Cauldron Familiar enters, it triggers, causing each opponent to lose 1 life and you to gain 1 life.
3. Activate Ashnod's Altar by sacrificing Cauldron Familiar.
4. When Cauldron Familiar dies, Mortuary triggers, putting Cauldron Familiar from your graveyard onto the top of your library.
5. Repeat.

This loop turns a humble cat into an infinite engine by leveraging a clever conservation of resources. With Bolas's Citadel allowing you to play Cauldron Familiar directly off the top of your library for life instead of mana, every iteration feeds Ashnod's Altar to generate colorless energy while Mortuary dutifully catches the cat upon death and places it right back where the Citadel can see it. Meanwhile, Cauldron Familiar's own entry trigger drains your opponents dry and pads your life total to keep paying for the Citadel's alternate cost, creating a self-sustaining cycle of eternal sacrifice.