Reverse Engineer

Improvise can't be used to pay for anything other than the cost of casting the spell. For example, it can't be used during the resolution of an ability that says “Counter target spell unless its controller pays 3 generic mana .”

When using improvise to cast a spell with X generic mana in its mana cost, first choose the value for X. That choice, plus any cost increases or decreases, will determine the spell's total cost. Then you can tap artifacts you control to help pay that cost. For example, if you cast Saheeli's Directive and choose X to be 3, the total cost is 3 generic mana red mana red mana red mana . If you tap two artifacts, you'll have to pay 1 generic mana red mana red mana red mana .

If an artifact you control has a mana ability with tap in the cost, activating that ability while casting a spell with improvise will result in the artifact being tapped when you pay the spell's costs. You won't be able to tap it again for improvise. Similarly, if you sacrifice an artifact to activate a mana ability while casting a spell with improvise, that artifact won't be on the battlefield when you pay the spell's costs, so you won't be able to tap it for improvise.