Cauldron of Souls + Dross Scorpion + Arsenal Thresher + Umbral Collar Zealot

Cauldron of Souls

Dross Scorpion

Arsenal Thresher

Umbral Collar Zealot

How it works

1. Activate Cauldron of Souls by tapping it, giving Arsenal Thresher persist until end of turn.
2. Activate Umbral Collar Zealot by sacrificing Arsenal Thresher.
3. When Arsenal Thresher dies, its persist ability and Dross Scorpion trigger.
4. Resolve the Dross Scorpion trigger, untapping Cauldron of Souls.
5. Resolve the Arsenal Thresher trigger, returning it from your graveyard to the battlefield with a -1/-1 counter on it, and then choosing to reveal at least one artifact card from your hand to remove the -1/-1 counter.
6. Resolve the Umbral Collar Zealot ability, putting a +1/+1 counter on it.
7. Repeat.