Mortuary + Bolas's Citadel + Blood Pet + Embalmed Ascendant

Mortuary

Bolas's Citadel

Blood Pet

Embalmed Ascendant

How it works

1. Activate Blood Pet by sacrificing it.
2. When Blood Pet dies, Mortuary and Embalmed Ascendant trigger.
3. Resolve the Mortuary trigger, putting Blood Pet from your graveyard onto the top of your library.
4. Resolve the Embalmed Ascendant trigger, causing you to gain 1 life and each opponent to lose 1 life.
5. Cast Blood Pet from the top of your library by paying 1 life.
6. Repeat.

This clever loop leverages the alternate cost of Bolas's Citadel to cast Blood Pet directly from the top of your library for just 1 life instead of paying mana. When you sacrifice Blood Pet for black mana, Mortuary catches it on the way to the graveyard and immediately places it right back onto the top of your library where Bolas's Citadel can see it again. Meanwhile, Embalmed Ascendant acts as the win condition and engine fuel: its max speed ability drains your opponents and gains you life whenever creatures die, which easily offsets the life paid to the Citadel while simultaneously ticking up your engine's speed.