The Last Agni Kai is a rare Instant card from Avatar: The Last Airbender (TLA), collector number 314. Current market price: $3.33 (foil $5.17), TCGplayer market prices via Scryfall.
Target creature you control fights target creature an opponent controls. If the creature the opponent controls is dealt excess damage this way, add that much {R}. Until end of turn, you don't lose unspent red mana as steps and phases end.