Mortuary + Ashes of the Abhorrent + Bolas's Citadel + Spore Frog

Mortuary

Ashes of the Abhorrent

Bolas's Citadel

Spore Frog

How it works

1. Activate Spore Frog by sacrificing it.
2. When Spore Frog dies, Mortuary and Ashes of the Abhorrent trigger.
3. Resolve the Mortuary trigger, putting Spore Frog from your graveyard onto the top of your library.
4. Resolve the Ashes of the Abhorrent trigger, causing you to gain 1 life
5. Resolve the Spore Frog ability.
6. Cast Spore Frog from the top of your library by paying 1 life.
7. Repeat.