Vexing Shusher and Counterbalance

[Polynomial P]

Lets say I have a Vexing shusher in play:

Vexing Shusher

Vexing Shusher can't be countered.
R/G Mana: Target spell can't be countered by spells or abilities.

And my opponent has a counterbalance in play. I play spell X and the triggered ability of Counterbalance is on the stack. My opponent responds by using top.

Question is: Do I have to make the spell uncounterable before the person reveals for counterbalance? Or, can I wait till they reveal and see if it matches the cmc of spell X, then make it uncounterable with Shusher?

[SadPanda]

You must respond to either the trigger or top activation since revealing is part of the resolution of counterbalance's ability.

[wraith985]

As far as I know, you have to make it uncounterable before the reveal. Once the trigger resolves and the reveal happens, the countering can't be responded to because it's all part of resolving the trigger and neither player gets priority until resolution is done.