Firebending is an ability that generates red mana whenever a creature with firebending attacks. That mana lasts until the end of combat, encouraging you to cast spells or activate abilities while combat is still underway.
Fire Lord Sozin provides firebending 3 alongside a combat-damage payoff, while Ran and Shaw combine firebending with Dragon support. Fire Nation Cadets gains firebending when a Lesson is in your graveyard.