Arc Reactor

Improvise is a static ability that functions while the spell with improvise is on the stack. “Improvise” means “For each generic mana in this spell’s total cost, you may tap an untapped artifact you control rather than pay that mana.”

The improvise ability isn’t an additional or alternative cost and applies only after the total cost of the spell with improvise is determined.

Multiple instances of improvise on the same spell are redundant.