Mortuary + Ashnod's Altar + Bolas's Citadel + Serrated Scorpion

Mortuary

Ashnod's Altar

Bolas's Citadel

Serrated Scorpion

How it works

1. Activate Ashnod's Altar by sacrificing Serrated Scorpion.
2. When Serrated Scorpion dies, it and Mortuary triggers.
3. Resolve the Mortuary trigger, putting Serrated Scorpion from your graveyard onto the top of your library.
4. Resolve the Serrated Scorpion trigger, causing you to gain 2 life and dealing 2 damage to each opponent.
5. Resolve the Ashnod's Altar ability.
6. Cast Serrated Scorpion from the top of your library by paying 1 life due to Bolas's Citadel.
7. Repeat.

This looping masterpiece is powered by Bolas's Citadel, which replaces the mana costs of your spells with life payments so you can cast cards directly from the top of your library. By sacrificing Serrated Scorpion to Ashnod's Altar, you generate a pair of crucial triggers: Ashnod's Altar yields the colorless mana you need while Mortuary neatly redirects the Scorpion straight back to the top of your library. As the Scorpion dies, its own drain ability triggers to offset the life spent casting it, letting this self-sustaining engine repeat endlessly to drain your opponents out of the game.