Counterbalance and Vexing Shusher

[Bryant Cook]

Must you pay mana before the revealing of Counterbalance?

[Cait_Sith]

Yes.

The card being revealed and the countering of the spell are both done as part of the ability's resolution.

[Jander78]

Must you pay mana before the revealing of Counterbalance?
Yes. If a card is revealed from Counterbalance the ability has already resolved. The only time you have to respond is when the ability is on the stack (I.e. before the card has been revealed.)