Mortuary + Dross Harvester + Phyrexian Dreadnought + Gwenom, Remorseless

Mortuary

Dross Harvester

Phyrexian Dreadnought

Gwenom, Remorseless

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 Dross Harvester trigger.
4. Resolve the Mortuary trigger, putting Phyrexian Dreadnought from your graveyard onto the top of your library.
5. Resolve the Dross Harvester trigger, causing you to gain 2 life
6. Repeat.

This wicked loop sets up a self-sustaining engine right off the top of your library, fueled by Gwenom, Remorseless granting you the ability to cast creatures from your library while trading mana costs for life payments. You drop Phyrexian Dreadnought for a single measly point of life, only for it to immediately trigger its own sacrifice clause upon entering the battlefield. That death sends the Dreadnought straight back to the top of your library thanks to Mortuary, while Dross Harvester steps in with its passive lifegain trigger to heal away the life you spent casting it.