I - Rules
(see FAQ 1.3, p. 17)
|Effect:||Play after a monster has made a successful melee or ranged attack against you (a melee or ranged attack that doesn't miss).
You must roll a power die. If the result is a surge, there is no effect.
If the result is not a surge, that monster's attack against you becomes a miss.
Does the attack miss all of its targets, or only the hero who played the card (the card says the "attack against you becomes a miss")?
Because you are changing a die to a miss result, all heroes targeted by the attack would evade the attack.