Mortuary + Bolas's Citadel + Viscera Seer + Carmen, Cruel Skymarcher

Mortuary

Bolas's Citadel

Viscera Seer

Carmen, Cruel Skymarcher

How it works

1. Activate Viscera Seer by sacrificing it.
2. When Viscera Seer dies, Mortuary and Carmen trigger.
3. Resolve the Mortuary trigger, putting Viscera Seer 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 Viscera Seer ability.
6. Cast Viscera Seer from the top of your library by paying 1 life.
7. Repeat.

This elegant loop lets you sacrifice and recast Viscera Seer indefinitely, completely bypassing normal mana costs by converting your life total into currency via Bolas's Citadel. Whenever you sacrifice a creature, Mortuary steps in to neatly recycle it straight to the top of your library so Bolas's Citadel can immediately play it again. Meanwhile, Carmen, Cruel Skymarcher gracefully capitalizes on the revolving door of sacrifices by stacking endless life and ever-growing +1/+1 counters onto herself with every iteration.