Deft Dismissal

• WWizards of the Coast2017-02-09
  Official Ruling
  You choose how many targets Deft Dismissal has and how the damage is divided as you cast the spell. Each target must receive at least 1 damage.
• WWizards of the Coast2017-02-09
  Official Ruling
  If some (but not all) of the targets become illegal, the original division of damage still applies, but no damage is dealt to illegal targets. If all targets become illegal, Deft Dismissal doesn’t resolve.

Rulings via Scryfall