Mortuary + Vindictive Vampire + Bolas's Citadel + Blood Pet

Mortuary

Vindictive Vampire

Bolas's Citadel

Blood Pet

How it works

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

This elegant little loop turns a humble Blood Pet into an infinite source of life, damage, and black mana by exploiting the interaction between your library and graveyard. With Mortuary ensuring that every creature sent to the graveyard simply returns to the top of your library, Bolas's Citadel allows you to play it right back out again without missing a beat. Since Bolas's Citadel replaces mana costs with life payments, Blood Pet's sacrifice ability generates net-positive mana while triggering Vindictive Vampire to steadily drain your opponents out of the game.