Mortuary + Mogg Fanatic + Bolas's Citadel + Vengeful Bloodwitch

Mortuary

Mogg Fanatic

Bolas's Citadel

Vengeful Bloodwitch

How it works

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

This cunning loop centers around Mogg Fanatic, which you sacrifice to deal 1 damage to any target before dying to fuel the combo. Because Bolas's Citadel allows you to cast spells directly from the top of your library by paying life instead of mana, you can immediately replay the goblin for just 1 life. Meanwhile, Mortuary ensures your sacrificed creature never stays in the graveyard, instantly placing it right back onto the top of your library for the Citadel to catch. Vengeful Bloodwitch rounds out the engine by turning every single iteration of this cycle into a guaranteed drain of your opponent's life total while simultaneously recovering the life you spent casting through the Citadel.