What it does
Firebending isn't a standard Magic: The Gathering keyword—it doesn't appear in any official rules or card set. You may be thinking of a mechanic from a custom set, a fan-made card, or possibly confusing it with the Avatar: The Last Airbender universe (which, as of now, isn't part of MTG's Universes Beyond).
If you encountered "Firebending" on a card, it's almost certainly a homebrew or proxy creation, and its rules would be defined by whoever designed it—not by the official comprehensive rules. Always check the card's own reminder text and confirm with your playgroup before using it in a game.
If you meant a real ability—like Firebreathing (an informal nickname for ":R: +1/+0" pump effects), or keywords like Prowess, Bushido, or Exalted—let me know and I'll give you an accurate breakdown of how it works in Commander.













