Mortuary + Aetherflux Reservoir + Bolas's Citadel + Yahenni, Undying Partisan

Mortuary

Aetherflux Reservoir

Bolas's Citadel

Yahenni, Undying Partisan

How it works

1. Activate Yahenni by sacrificing a creature
2. When the creature dies, Mortuary triggers, putting the creature from your graveyard onto the top of your library.
3. Resolve the Yahenni ability.
4. Cast the creature from the top of your library by paying X life, where X is the creature's mana value.
5. Aetherflux Reservoir triggers, causing you to gain 1 life for each spell you've cast this turn.
6. Repeat.

This loop is a masterclass in recycling, fueled by Bolas's Citadel allowing you to bypass mana costs and cast that creature directly from the top of your library by paying life instead. As you continuously sacrifice that creature to Yahenni, Undying Partisan's ability, Mortuary immediately intercepts it on the way to the graveyard and stacks it right back on top of your library for the Citadel to grab again. Meanwhile, Aetherflux Reservoir watches the endless chain of spells being cast and rewards your life-payment cycle with massive, rapidly escalating lifegain, ensuring you never run out of fuel before you can point its ultimate ability at an opponent.