Mortuary + Bile Urchin + Bolas's Citadel + South Wind Avatar

Mortuary

Bile Urchin

Bolas's Citadel

South Wind Avatar

How it works

1. Activate Bile Urchin by sacrificing it.
2. When Bile Urchin dies, Mortuary and South Wind Avatar trigger.
3. Resolve the Mortuary trigger, putting Bile Urchin from your graveyard onto the top of your library.
4. Resolve the South Wind Avatar trigger, causing you to gain 1 life.
5. South Wind Avatar triggers, causing each opponent to lose 1 life.
6. Resolve the Bile Urchin ability.
7. Cast Bile Urchin from the top of your library by paying 1 life.
8. Repeat.