Mortuary + Goblin Firestarter + Gwenom, Remorseless + Arnyn, Deathbloom Botanist

Mortuary

Goblin Firestarter

Gwenom, Remorseless

Arnyn, Deathbloom Botanist

How it works

1. Cast Goblin Firestarter by paying its mana cost.
2. Activate Goblin Firestarter by sacrificing it.
3. When Goblin Firestarter dies, Mortuary and Arnyn trigger.
4. Resolve the Mortuary trigger, putting Goblin Firestarter 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 Goblin Firestarter from the top of your library by paying 1 life.
7. Repeat from step 2.