Mortuary + Bolas's Citadel + Moonlit Wake + Phyrexian Dreadnought

Mortuary

Bolas's Citadel

Moonlit Wake

Phyrexian Dreadnought

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 Moonlit Wake trigger.
4. Resolve the Mortuary trigger, putting Phyrexian Dreadnought from your graveyard onto the top of your library.
5. Resolve the Moonlit Wake trigger, causing you to gain 1 life
6. Repeat.

This loop turns the terrifying self-sacrifice of Phyrexian Dreadnought into a perpetual engine by pairing it with Mortuary, which instantly redirects the doomed 12/12 right back to the top of your library. From there, Bolas's Citadel allows you to play the Dreadnought straight off the top for a mere 1 life instead of its traditional mana cost, seamlessly feeding the cycle anew. Meanwhile, Moonlit Wake counters that life payment entirely by granting you 1 life every time the Dreadnought hits the graveyard, netting you positive life with every single iteration.