Ancient Adamantoise + Nim Deathmantle + Krark-Clan Ironworks + Umbral Collar Zealot

Ancient Adamantoise

Nim Deathmantle

Krark-Clan Ironworks

Umbral Collar Zealot

How it works

1. Activate Umbral Collar Zealot by sacrificing Ancient Adamantoise.
2. When Ancient Adamantoise dies, it and Nim Deathmantle trigger.
3. Resolve the Nim Deathmantle trigger, causing you to pay 4 to return Ancient Adamantoise from your graveyard to the battlefield and attach Nim Deathmantle to it.
4. Resolve the Ancient Adamantoise trigger, creating ten tapped Treasure tokens.
5. Resolve the Umbral Collar Zealot ability.
6. Activate Krark-Clan Ironworks twice by sacrificing two Treasures, adding CCCC.
7. Repeat.

This loop turns Ancient Adamantoise into an infinite engine by leveraging its massive dying reward. With Nim Deathmantle standing ready to return the creature to the battlefield for four mana whenever it hits the graveyard, Umbral Collar Zealot provides the initial sacrifice outlet to get the cycle rolling. To fund the Deathmantle's revival cost, Krark-Clan Ironworks happily devours two of the ten tapped Treasure tokens produced by the Adamantoise's death trigger, generating a net surplus of colorless mana while fueling infinite loops of death, sacrifices, and surveils.