THIS IS A POSSIBLE SPOILER / THEORY AND IF YOU DON'T WANT ANYTHING TO DO WITH IT PLEASE DON'T READ ANYTHING BELOW
So I was watching the CE unboxing video with the woman taking everything out and showcasing it. And I noticed something when she opened the art book.
The first thing you see is a "female" demon i'm only assuming it is Mephistos daughter. But if you look to the left there is a picture of a demon that seems to have a tail made out of BONE and quite a lot of bones sticking out. Could this possibly be a newer remodel of Mephisto? Granted Mephisto is described as a floating demon with a tail that forms from his spine. But I have this weird theory that this could possibly be him. I could be completely and utterly wrong and just ignorant in my theory. But it would be kind of cool if it was him.
I mean it is a page RIGHT next to his daughter's art.
EDIT: I would also like to point out the picture furthest to the left, is it that picture of Mephisto floating with his back to the ground? I can't quite make it out.