Some are proven to be skull deformation. Some are anomolous (like the mayan crystal skulls) and the "
Star Child"
http://www.lloydpye.com/starchildskull.htm
Some skull's cant be explained by deformation.
I'm fairly empathic and I think that the video I linked of the sick alien is fairly real. There's another one that got leaked by private security from a site in Mexico or Mexico city where there's a lone alien being held captive in a room.
I'm not 100% sure they are ETs though. They may be some indigenous species or experiment/mutant.