I think it's more likely that he's a character we haven't met yet. Though I can also see the possibility of his being Kizaki. But then again Kizaki could be a red herring.
It could likely be. It wouldn't susprise me if Kizaki was secretly working with Wiseman and the Phantoms.
Wiseman must be humans.
He must've created the Phantoms himself. He has to be human and a mage like the White Wizard.
If he Wiseman is human, is it possible for him to transform into a Phantom too?
I think it's more likely that he's a character we haven't met yet. Though I can also see the possibility of his being Kizaki. But then again Kizaki could be a red herring.