Excavation Explosion deals 3 damage to any target. Create a tapped Powerstone token. (It's an artifact with ": Add . This mana can't be spent to cast a nonartifact spell.")
Urza's engineers could take weeks to dig out a powerstone. The goblins weren't so painstaking.
: Add 
. This mana can't be spent to cast a nonartifact spell.")
