The wavy cracks you see on the back of the skull is the result of the skull merging together as you grow. At birth your frontal and parietal bone aren't connected. The 'crack' is called The Coronal Suture
I feel that the cracks in the skull should be a bit more subtle. Also in the image you posted last page, I saw subtle lines sticking out of the cracks. Most demons in the cinematic from blizzard have some characteristic feature, maybe something to have a look at. Awesome project, you're doing great. I'm very interested in…
Aaand I'm back! @Limewax, thanks for your honest feedback! I can see there are some holes in my animatic and I'm in the progress of figuring out how to resolve it. Anyways, so I'm gonna put the animatic on hold until I get some ideas on how to fix the problems. While we are waiting I've made my skull basemesh that I'm…