Charity Tail and Unown G

[hueglin]

Ambipom MT' "Charity Tail" attack says "Before Ambipom does damage, your opponent may discard 2 cards from his or her hand. If he or she does, this attack's base damage is 10 instead of 80."

I'm wondering if the discarding of 2 cards would be an effect of the attack other than damage, and thus be prevented, thereby causing the attack to always do 80 damage on a Pokemon with Unown G attached?

 

[PokePop]

It is an effect of the attack, but not an effect done to the protected Pokemon.
It is an optional effect that the defending player can choose to invoke and use on their hand.
Unown G has no impact on it.