Avatar Roku, Firebender is a mythic Legendary Creature — Human Avatar card from Avatar: The Last Airbender Eternal (TLE), collector number 112. Current market price: $11.58 (foil $12.46), TCGplayer market prices via Scryfall.
Whenever a player attacks, add six {R}. Until end of combat, you don't lose this mana as steps end. {R}{R}{R}: Target creature gets +3/+0 until end of turn.