I'd flip a coin. Heads = Fire/???(chosen from a roulette of the other 14 types) Tails = Fire/Fighting --- I am The Defender of Darkness. The Knight of Nothingness. The Master of Murkiness. I am the Keeper of Shadows, AND I WILL RULE YOU!!
I would make it the first double-type Pokémon at Fire/Fire. 4x Water, Ground, and Rock weaknesses? NOBODY would use it, but people would still rejoice that it WAS NOT FIRE/FIGHTING!!!!!
I don't know, if it had good enough stats and move pool it could compensate for the typing, and I would love to see that double STAB. --- My Pokemon guide: pkmntrainercory.blogspot.com Check it out! Shinji X Asuka is the most sacred pairing in all of anime. That is an unnegotiable fact.