Mortuary + Bolas's Citadel + Blood Pet + Susurian Voidborn

Mortuary

Bolas's Citadel

Blood Pet

Susurian Voidborn

How it works

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

This loop turns the life-paying power of Bolas's Citadel into an infinite engine by leveraging Mortuary to recycle sacrificed creatures straight back to the top of your library. When you sacrifice Blood Pet for mana, Mortuary catches it on the way to the graveyard and stacks it right back on your library so Bolas's Citadel can cast it again for a mere 1 life instead of its mana cost. Meanwhile, Susurian Voidborn watches everything die to effortlessly drain your opponents out of the game while padding your life total to safely fuel more Citadel plays.