So I've noticed on a lot of sculpts that grayskull has a spine behind the head and seems very organic, like it used to be an actual serpos sized being at one time. Has this ever been alluded to in any media? If not it should have IMHO. It would be cool if king grayskull came to power because he defeated the creature and took its remainsbto build the castle!
I never thought Castle Grayskull was a former living being, I just believed it was a design choice to resemble a skull. I looked in the series bible, and on page 11 where it talks about Castle Grayskull, I see no mention of it as a former living being. And there's no other mention of it that I can find elsewhere to say it was some creature. So I'm going to say it was never a living being, however, the Castle does have an organic look to it. And clearly, those teeth on the castle look like real teeth of some kind, as well as the spine (on some renditions).
There's probably only one guy that can answer this question, and that would be artist Mark Taylor, who drew the original designs. What was his intent?