Cauldron of Souls + Dross Scorpion + Arsenal Thresher + Phyrexian Altar

Cauldron of Souls

Dross Scorpion

Arsenal Thresher

Phyrexian Altar

How it works

1. Activate Cauldron of Souls by tapping it, giving Arsenal Thresher persist until end of turn.
2. Activate Phyrexian Altar by sacrificing Arsenal Thresher, adding one mana of any color.
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. Repeat.

This ingenious loop relies on Cauldron of Souls to continuously grant persist to Arsenal Thresher, letting it tumble into the graveyard only to rise again. Each trip to the bin feeds Phyrexian Altar to generate an endless stream of colored mana while simultaneously triggering Dross Scorpion to untap your Cauldron for the next iteration. Meanwhile, Arsenal Thresher's own entry ability allows you to reveal artifact cards from your hand to place a +1/+1 counter on it as it enters, neatly neutralizing the -1/-1 counter from persist and keeping the mechanical cycle endlessly sustainable.