Mortuary + Bolas's Citadel + Phyrexian Dreadnought + Relic Vial

Mortuary

Bolas's Citadel

Phyrexian Dreadnought

Relic Vial

How it works

1. Cast Phyrexian Dreadnought from the top of your library by paying 1 life.
2. When Phyrexian Dreadnought enters, it triggers, causing you to sacrifice it.
3. When Phyrexian Dreadnought dies, Mortuary and Relic Vial trigger.
4. Resolve the Mortuary trigger, putting Phyrexian Dreadnought from your graveyard onto the top of your library.
5. Resolve the Relic Vial trigger, causing you to gain 1 life and each opponent to lose 1 life.
6. Repeat.

This insidious loop turns the top of your deck into a revolving door of colossal dread, fueled entirely by life rather than mana thanks to Bolas's Citadel. You simply cast Phyrexian Dreadnought over and over, paying a single meager point of life to do so before its own entry trigger forces it straight into the graveyard. Mortuary immediately catches it on the way down, neatly resting the great beast back onto the top of your library so Bolas's Citadel can grant access to it once more. Meanwhile, Relic Vial sits quietly on the battlefield reaping the harvest of your endless cycle of sacrifices, draining your opponents' life totals down to zero while padding your own life total to keep the Citadel's payments flowing freely.