I doubt I'll post more photo manipulation WIP, but since I saved all my progress versions of this one, I'll share the process with you.
First I cut my figure from the original photo which was taken in my bathroom (the only room in the house with proper light). The hair extracting was the biggest problem, as none of the techniques from popular tutorials worked on this photo, due to complex background. I should buy a white cloth for background.
I added two more photos, skull and brain. Trivia: the brain belongs to Charles Babbage, photo taken at the London Science Museum.
It's obvious brain photo is not really of desired quality...
...so I painted over it. I tried to follow the pattern of the photo beneath, but to add some new details as well (I googled for some references). I also desaturated the body photo.
Added a pair of bat wings — now this was harder than I thought, because I had no idea how it would look in reality — I mean the shoulder blade, and that anatomical stuff. This was the best I could do without making myself look like Quasimodo.
I also arranged some kind of background with paper and canvas textures.
I decided on the fiery background, so I assembled the fire from a few photos, and painted some parts.
I also tried to make a realistic brand (I found a tutorial on this, but some steps were not giving the right results, so I improvised).
I decided on the red hair, so I painted it in a few reddish shades, but added some of the original hair texture so that it doesn't stand out too much from the rest. I added a paper texture on top of everything because I just like textures.
Finished work can be seen here, and here's a few details at 50% size: