The Last Agni Kai - Avatar: The Last Airbender - 314

Instant

Mana Cost: {1}{R}

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.

Rare · Avatar: The Last Airbender · #314 (TLA)

Illustrated by Dominik Mayer