Power Spray v Flip Powers

[SuicidalPikachu]

Ok, i asked this awhile ago in league. Say my opponent is using Dialga lvX GE

They use Time Skip, and i have a Power Spray in my hand. Can i hold it until i see the result of the flip, and if it is an outcome i dislike, use power spray to cancel it, or do i have to declare power spray before the outcome of the flips?

 

[PokePop]

Do you think you should be able to get the knowledge of success or failure before stopping them from using the Power?

No, that would be unfair.

You have to block the Power before the player has done it. YOu don't get to wait.