Mikaeus, the Unhallowed + Cauldron of Souls + Dross Scorpion + Ashnod's Altar

Mikaeus, the Unhallowed

Cauldron of Souls

Dross Scorpion

Ashnod's Altar

How it works

1. Activate Cauldron of Souls by tapping it, giving Dross Scorpion persist until end of turn.
2. Activate Ashnod's Altar by sacrificing Dross Scorpion, adding CC.
3. Dross Scorpion dies, triggering its ability, its undying ability and its persist ability.
4. Resolve the first Dross Scorpion trigger, untapping Cauldron of Souls.
5. Resolve the Dross Scorpion persist trigger, returning it from your graveyard to the battlefield with a -1/-1 counter on it.
6. Activate Ashnod's Altar by sacrificing Dross Scorpion, adding CC.
7. Dross Scorpion dies, triggering its ability and its undying ability.
8. Resolve the first Dross Scorpion trigger, untapping Cauldron of Souls.
9. Resolve the second Dross Scorpion trigger, returning it from your graveyard to the battlefield with a +1/+1 counter on it.
10. Activate Ashnod's Altar by sacrificing Dross Scorpion, adding CC.
11. Dross Scorpion dies, triggering its ability and its persist ability.
12. Repeat from step 4.

This clever loop relies on the fascinating interaction between undying and persist: when a creature has both +1/+1 and -1/-1 counters placed on it simultaneously, state-based actions cause them to annihilate each other, resetting the creature's counter tally entirely. Mikaeus, the Unhallowed provides the undying half to keep Dross Scorpion coming back, while Cauldron of Souls grants the persist half for the alternate iteration. Every time Dross Scorpion is sacrificed to Ashnod's Altar for mana, its death triggers Dross Scorpion itself to untap Cauldron of Souls, creating a self-sustaining engine of infinite sacrifices, triggers, and colorless mana.