Pit Fight

Fight was green's negotiated settlement with the color pie: a color forbidden direct burn could still kill a creature, provided it paid for the privilege by risking its own attacker in the exchange. Pushing that fight to instant speed is the lever the sorcery-bound versions never pulled. At instant speed the effect becomes a combat trick: you can wait for an opponent to commit to an attack or block, then snap your creature into theirs with the damage already resolved around their decision. The hybrid pip is the other lever. Because can be paid with either color, the card slots into mono-red, mono-green, or any overlap of the two without straining a manabase, broadening its home far past Gruul. The structural weakness is the one every fight spell carries: both creatures take damage, so your attacker has to outsize the target or trade down. It also leaves the spell fragile in a way burn never is. Both targets are locked in on cast, so if an opponent removes one of the two creatures in response, the spell still resolves as much as it can, but no fight damage is dealt: a fight requires both creatures, and with one gone there is nothing for the survivor to fight. Your two mana buys nothing. That combination (symmetric damage, plus the ease of neutralizing it by killing either half) is the cost of handing green and red an instant-speed answer to a creature without handing them a Lightning Bolt.