Mortuary + Bile Urchin + Bolas's Citadel + Blood Artist

Mortuary

Bile Urchin

Bolas's Citadel

Blood Artist

How it works

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

This clever loop relies on Bolas's Citadel to let you cast creatures directly from the top of your library by paying life instead of mana. When you sacrifice Bile Urchin to its own ability, Mortuary immediately intervenes to place it right back on top of your library, making it endlessly recasting-eligible. Meanwhile, Blood Artist watches the carnage unfold, turning every iteration into a net-neutral life exchange that easily outpaces the Citadel's life payment.