Aerial Volley deals 3 damage divided as you choose among one, two, or three target creatures with flying.
6/22/2015 You choose how many targets Aerial Volley has and how the damage is divided as you cast the spell. Each target must receive at least 1 damage.
6/22/2015 If some (but not all) of the targets become illegal before Aerial Volley tries to resolve, the original division of damage still applies, but no damage is dealt to illegal targets. If all targets become illegal, Aerial Volley won’t resolve.