Cone of Flame

Oracle Text

Cone of Flame deals 1 damage to any target, 2 damage to another target, and 3 damage to a third target.

Card Rulings

7/18/2014 Each of the three targets must be different. If there aren’t three different legal targets available, you can’t cast the spell.
7/18/2014 If one or two of Cone of Flame’s targets are illegal when it resolves, you can’t change how much damage will be dealt to the remaining legal targets.