Actually, Junior humanized himself. He used his morphic tentacles to imitate his human/pure soul look so that Mimi would recognize him.
Also, as you can see, his blood is green, which is the color of the Nergal blood. He isn't actually hurt. Just...very inconvenienced, being spineless and all. He can perfectly survive being decapitated after all and as long as he has his eye, he can use his Nergal power to compensate for any lost limb. Or body. They're just hard to control.