Mortuary + Aetherflux Reservoir + Umbral Collar Zealot + Bolas's Citadel

Mortuary

Aetherflux Reservoir

Umbral Collar Zealot

Bolas's Citadel

How it works

1. Activate Umbral Collar Zealot by sacrificing a creature with mana value 1 or less.
2. When the creature dies, Mortuary triggers, putting the creature from your graveyard onto the top of your library.
3. Resolve the Umbral Collar Zealot ability.
4. Cast the creature from the top of your library by paying 1 life.
5. Aetherflux Reservoir triggers, causing you to gain 1 life
6. Repeat.

This clever loop lets you turn life into a self-sustaining engine by utilizing Bolas's Citadel to cast cheap creatures directly from the top of your library for life instead of mana. Each time you cast that creature, Aetherflux Reservoir triggers to offset your life payment with an escalating lifegain bonus, while Umbral Collar Zealot provides the sacrifice outlet needed to fuel the cycle. Whenever the sacrificed creature hits your graveyard, Mortuary immediately tucks it right back onto the top of your library so you can play it all over again.