Mortuary + Bolas's Citadel + Viscera Seer + Susurian Voidborn

Mortuary

Bolas's Citadel

Viscera Seer

Susurian Voidborn

How it works

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

This loop sets up a self-sustaining engine using Viscera Seer to sacrifice itself over and over, feeding right back into the top of your library via Mortuary. Because Bolas's Citadel lets you cast spells straight from the top of your library by paying life instead of mana, you can immediately replay the seer for a mere 1 life. Meanwhile, Susurian Voidborn watches every sacrifice happen, turning each iteration into a guaranteed life drain for your opponents and a life buffer for you.