Mortuary + Bolas's Citadel + Phyrexian Dreadnought + Overgrowth Elemental

Mortuary

Bolas's Citadel

Phyrexian Dreadnought

Overgrowth Elemental

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

This loop turns your library into a self-sustaining engine by leveraging Bolas's Citadel to cast creatures directly from the top, bypassing mana costs entirely at the mere price of your life total. Phyrexian Dreadnought serves as the cheap catalyst, instantly heading to the graveyard upon entry due to its own self-sacrificing trigger and neatly fueling Overgrowth Elemental's drain-and-gain tracking. Meanwhile, Mortuary catches the dreadnought the moment it hits the graveyard and immediately tucks it back onto the top of your library. Because Overgrowth Elemental passively refunds your life total whenever creatures die, you easily offset the life payments required by Bolas's Citadel, letting you churn through this cycle indefinitely.