Interesting interpretation of the prompt. Some kind of sonnet form, but I'm not up on the differences between the various ones, so I'm not sure which. Lull/hull/all may be a bit of a weak rhyme, and "macabre" doesn't seem to fit the rhythm, but the rest all works well. Nice musing on how people find skulls so unnerving. Alas, poor Yorick. I knew him, Horatio.

Poetry's kind of odd sometimes. Like here, once I've read it once already, it's very clear that your first mention of the skull is introducing it as the subject. But on a first read, I just figured it was a piece of imagery and glossed over it without that sinking in until later. But that's on me, as I don't think I would have made a different choice of how to frame it.