Mortuary + Carmen, Cruel Skymarcher + Bile Urchin + Bolas's Citadel

Mortuary

Carmen, Cruel Skymarcher

Bile Urchin

Bolas's Citadel

How it works

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

This loop sets up an insidious engine of life and death, turning a humble goblin into an endless cycle of sacrifice. When you sacrifice Bile Urchin, Mortuary ensures the creature immediately returns to the top of your library rather than lingering in the graveyard, while Carmen, Cruel Skymarcher rewards the sacrifice by growing stronger and restoring the life you spend. Bolas's Citadel ties the whole operation together by allowing you to bypass mana costs entirely, letting you recast Bile Urchin straight from the top of your library for a mere pittance of life and repeating the cycle infinitely.