Metalwork Colossus + Slagstone Refinery + Sly Requisitioner + Ashnod's Altar

Metalwork Colossus

Slagstone Refinery

Sly Requisitioner

Ashnod's Altar

How it works

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