This was written by Norrin.

It was kind of a challenge to portray a thing missing its own skull, especially if it's wearing another skull on top of it. So there it is without its exoskull, and that's what a Cubone looks like without its endoskull. (Or maybe that's just what they look like, which makes this comic less funny and more creepy.)
Also Norrin wants to tell you that he thinks it looks like the penguin thing from Bloom County.