Metalwork Colossus

If the total mana value of noncreature artifacts you control is 11 or greater, Metalwork Colossus costs 0 generic mana to cast.

The total cost to cast Metalwork Colossus is locked in before you pay that cost. For example, if you control three noncreature artifacts each with mana value 2, including one you can sacrifice to add colorless mana , the total cost of Metalwork Colossus is 5 generic mana . Then you can sacrifice the artifact when you activate mana abilities just before paying the cost.

Once a player has announced that they are casting Metalwork Colossus, no player may take actions to try to change the number of artifacts its controller controls before that spell's cost is locked in.