If an artifact spell has {X} in its mana cost, choose the value for X first, and then reduce the cost by {1}. For example, an artifact that costs {X} with X chosen as 4 costs {3} to cast if you control Foundry Inspector.
20 Sept 2016
Once a player has announced an artifact spell, no player may take actions to try to remove Foundry Inspector from the battlefield before that spell's cost is locked in.