Mortuary + Falkenrath Noble + Bolas's Citadel + Blood Pet

Mortuary

Falkenrath Noble

Bolas's Citadel

Blood Pet

How it works

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

This clever loop turns the top of your library into an endless loop of sacrifice and rebirth by leveraging Bolas's Citadel to cast spells using life instead of mana. When you sacrifice Blood Pet for black mana, Mortuary catches it on its way to the graveyard and immediately places it back onto the top of your library. Meanwhile, Falkenrath Noble watches the carnage, draining your opponents and recovering the life you spent to cast the Blood Pet right back off the Citadel.