Banefire | Magic: The Gathering
Formats Banefire is Legal in
Official Oracle Text for Banefire
If X is 5 or more, Banefire can't be countered by spells or abilities and the damage can't be prevented.
Official Rulings for Banefire
2/1/2009 : Banefire can be targeted by spells that try to counter it (such as Countersquall) 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.
2/1/2009 : Banefire's ability won't prevent it from being countered by the game rules if its target has become an illegal target.