Mortuary + Bolas's Citadel + Viscera Seer + Vein Ripper

Mortuary

Bolas's Citadel

Viscera Seer

Vein Ripper

How it works

1. Activate Viscera Seer by sacrificing it.
2. When Viscera Seer dies, Mortuary and Vein Ripper trigger.
3. Resolve the Mortuary trigger, putting Viscera Seer from your graveyard onto the top of your library.
4. Resolve the Vein Ripper trigger, causing you to gain 2 life and target opponent to lose 2 life.
5. Resolve the Viscera Seer ability.
6. Cast Viscera Seer from the top of your library by paying 1 life.
7. Repeat.

This clever loop turns your library into an endless engine by using Bolas's Citadel to cast creatures directly off the top for a mere life payment instead of their mana cost. When you sacrifice Viscera Seer to its own ability, Mortuary immediately catches it on the way to the graveyard and slides it right back onto the top of your library to be played again. Meanwhile, Vein Ripper hangs out to weaponize all those deaths, draining your opponents' life totals and padding your own life total to comfortably fuel Bolas's Citadel's life-paying requirements.