Mortuary + Cauldron Familiar + Bolas's Citadel + Umbral Collar Zealot

Mortuary

Cauldron Familiar

Bolas's Citadel

Umbral Collar Zealot

How it works

1. Cast Cauldron Familiar either from your hand or from the top of your library by paying or 1 life respectively.
2. When Cauldron Familiar enters, it triggers, causing each opponent to lose 1 life and you to gain 1 life.
3. Activate Umbral Collar Zealot by sacrificing Cauldron Familiar.
4. When Cauldron Familiar dies, Mortuary triggers, putting Cauldron Familiar from your graveyard onto the top of your library.
5. Resolve the Umbral Collar Zealot ability.
6. Repeat.

This ingenious engine lets you cast Cauldron Familiar straight from the top of your library for life instead of mana, thanks to Bolas's Citadel's alternative casting cost. Once the cat enters, it drains your opponents while Mortuary ensures it neatly returns to the top of your library the moment Umbral Collar Zealot sacrifices it. You can even use Umbral Collar Zealot's surveil ability to clean away unwanted draws, letting the Citadel keep playing the familiar over and over in a seamless loop.