Metalwork Colossus + Pitiless Plunderer + Slagstone Refinery + Ashnod's Altar

Metalwork Colossus

Pitiless Plunderer

Slagstone Refinery

Ashnod's Altar

How it works

1. Activate Ashnod's Altar by sacrificing Metalwork Colossus, adding CC.
2. When Metlwork Colossus dies, Slagstone Refinery and Pitiless Plunderer trigger.
3. Resolve the Slagstone Refinery trigger, creating a tapped Powerstone artifact creature token.
4. Resolve the Pitiless Plunderer trigger, creating a Treasure artifact token.
5. Activate Metalwork Colossus by sacrificing the Powerstone token and the Treasure token, returning Metalwork Colossus from your graveyard to your hand.
6. Cast Metalwork Colossus by paying at most 1.
7. Repeat.