Mortuary + Wild Cantor + Bolas's Citadel + Arnyn, Deathbloom Botanist

Mortuary

Wild Cantor

Bolas's Citadel

Arnyn, Deathbloom Botanist

How it works

1. Cast Wild Cantor by paying its mana cost.
2. Activate Wild Cantor by sacrificing it.
3. When Wild Cantor dies, Mortuary and Arnyn trigger.
4. Resolve the Mortuary trigger, putting Wild Cantor from your graveyard onto the top of your library.
5. Resolve the Arnyn trigger, causing target opponent to lose 2 life and you to gain 2 life.
6. Cast Wild Cantor from the top of your library by paying 1 life.
7. Repeat from step 2.