Mortuary + Bolas's Citadel + Proper Burial + Accursed Centaur

Mortuary

Bolas's Citadel

Proper Burial

Accursed Centaur

How it works

1. Cast Accursed Centaur by paying its mana cost.
2. Activate Accursed Centaur by sacrificing it.
3. When Accursed Centaur dies, Mortuary and Proper Burial trigger.
4. Resolve the Mortuary trigger, putting Accursed Centaur from your graveyard onto the top of your library.
5. Resolve the Proper Burial trigger, causing you to gain at least 1 life.
6. Cast Accursed Centaur from the top of your library by paying 1 life.
7. Repeat from step 2.