Cone of Flame — ruling 1

Each of the three targets must be different. If there aren’t three different legal targets available, you can’t cast the spell.

Cone of Flame — ruling 2

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.

Cone of Flame : règles, fonctionnement et interactions (MTG)

Cone of Flame is one of those cards players keep asking about. Here is, in plain words, what its official text says, the rulings published by Wizards of the Coast, and the combos players actually run.

Official card text

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

How it works : Cone of Flame

Original English text — Wizards of the Coast / Scryfall

#1July 18, 2014· Wizards of the Coast
Each of the three targets must be different. If there aren’t three different legal targets available, you can’t cast the spell.
No other card is named in this ruling.
#2July 18, 2014· Wizards of the Coast
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.
No other card is named in this ruling.