Aerial Volley

• WWizards of the Coast2015-06-22
  Official Ruling
  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.
• WWizards of the Coast2015-06-22
  Official Ruling
  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.

Rulings via Scryfall