Mortuary + Bile Urchin + Bolas's Citadel + Grave Venerations

Mortuary

Bile Urchin

Bolas's Citadel

Grave Venerations

How it works

1. Cast Bile Urchin by paying its mana cost.
2. Activate Bile Urchin by sacrificing it.
3. When Bile Urchin dies, Mortuary and Grave Venerations trigger.
4. Resolve the Mortuary trigger, putting Bile Urchin from your graveyard onto the top of your library.
5. Resolve the Grave Venerations trigger, causing each opponent to lose 1 life and you to gain 1 life.
6. Cast Bile Urchin from the top of your library by paying 1 life.
7. Repeat from step 2.