Yeah a black flame via Adv CoA+flame from King would be also hype.
@DarkWitch
It doesn´t even need to be adv CoC, something rare like Katakuri get would be amazing for King.^^
He will have different weapons like he used those guns? Light beams? Sword, agility, possibly a special power from his rare tribe. If he had some special type of haki would be mentioned by now this is not how you do a character like that, we knew Kata had advanced CoO since his introduction.
King's strength so far will be hand to hand combat, agility due to his zoan, strong enough haki, sword and some guns here and there.