Mortuary + Fleshtaker + Bile Urchin + Bolas's Citadel

Mortuary

Fleshtaker

Bile Urchin

Bolas's Citadel

How it works

1. Activate Bile Urchin by sacrificing it.
2. When Bile Urchin dies, Mortuary and Fleshtaker trigger.
3. Resolve the Fleshtaker trigger, causing you to gain 1 life and scry 1.
4. Resolve the Mortuary trigger, putting Bile Urchin from your graveyard onto the top of your library.
5. Resolve the Bile Urchin ability.
6. Cast Bile Urchin from the top of your library by paying 1 life.
7. Repeat.

This clever little loop uses Mortuary as the engine to immediately recycle any creature sent to your graveyard right back to the top of your library. Bolas's Citadel makes casting that recycled creature effortless by letting you bypass mana costs entirely and pay life instead, which is easily offset by the steady stream of lifegain provided by Fleshtaker whenever you sacrifice a creature. Finally, Bile Urchin sits at the center of the action as both the sacrificial fodder and the win condition, allowing you to repeatedly drain your opponents out of the game through an endless cycle of death and rebirth.