Angel of serenity

[Antirayman]

My opponent casts an  {Angel of Serenity}.
It enters and he targets 3 creatures i control.
Does the abillity gets countered, when one of the targets leaves play?

[Fenster]

Good question!
I do believe so but im not really sure!

[Deathstorm]

I would say no because the card text says you may exile up to three.

RESOLVED

[Keyeto]

I would say no because the card text says you may exile up to three.

^ This right here. "Up to" means anywhere from 0-3. If all the targets became invalid, it wouldn't matter.

[Kaleo42]

Only when all targets are removed is an ability countered.

Take {hex} for example. You do need 6 targets to cast the spell, but not to resolve it.