Mortuary + Bolas's Citadel + Blood Pet + Relic Vial

Mortuary

Bolas's Citadel

Blood Pet

Relic Vial

How it works

1. Activate Blood Pet by sacrificing it.
2. When Blood Pet dies, Mortuary and Relic Vial trigger.
3. Resolve the Mortuary trigger, putting Blood Pet from your graveyard onto the top of your library.
4. Resolve the Relic Vial trigger, causing you to gain 1 life and each opponent to lose 1 life.
5. Cast Blood Pet from the top of your library by paying 1 life.
6. Repeat.

This ingenious loop turns a modest sacrifice into an infinite engine, powered entirely by life instead of mana. With Bolas's Citadel granting you the ability to cast spells directly from the top of your library for life rather than mana, you can repeatedly deploy Blood Pet for just a single point of life. Every time Blood Pet is sacrificed for black mana, Mortuary instantly catches it on the way to the graveyard, placing the creature right back on top of your library to keep the Citadel fueled. Meanwhile, Relic Vial leverages all those dying creatures to drain your opponents dry and pad your life total, ensuring you never run out of the vital resource you are spending to cast your spells.