Banefire — ruling 1

To determine whether it can be countered and its damage can be prevented, Banefire checks the number you chose for X, not the amount of mana you actually spent or the amount of damage it will actually deal.

Banefire — ruling 2

Banefire can be targeted by spells that try to counter it regardless of what the value of X is. If X is 5 or more, those spells will still resolve, but the part of their effect that would counter Banefire won’t do anything. Any other effects those spells have will work as normal.

Banefire — ruling 3

If its target is illegal by the time Banefire tries to resolve, the spell isn’t countered, but it doesn’t resolve. The target won’t be dealt damage.

Banefire : règles, fonctionnement et interactions (MTG)

Banefire 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

Banefire deals X damage to any target. If X is 5 or more, this spell can't be countered and the damage can't be prevented.

How it works : Banefire

Original English text — Wizards of the Coast / Scryfall

#1July 13, 2018· Wizards of the Coast
To determine whether it can be countered and its damage can be prevented, Banefire checks the number you chose for X, not the amount of mana you actually spent or the amount of damage it will actually deal.
No other card is named in this ruling.
#2July 13, 2018· Wizards of the Coast
Banefire can be targeted by spells that try to counter it regardless of what the value of X is. If X is 5 or more, those spells will still resolve, but the part of their effect that would counter Banefire won’t do anything. Any other effects those spells have will work as normal.
No other card is named in this ruling.
#3July 13, 2018· Wizards of the Coast
If its target is illegal by the time Banefire tries to resolve, the spell isn’t countered, but it doesn’t resolve. The target won’t be dealt damage.
No other card is named in this ruling.