A Spider-Man villain that I enjoyed while reading through all Spider-Man books was Vermin, especially in the storyline focused on him in Spectacular Spider-Man in the early '90s.
I knew making a custom of him wouldn't be very hard after I saw one using the head of the old 5" Vermin figure on the body of Werewolf by Night. Werewolf is the perfect choise of body, because they're almost identical, even with the half-torn green pants!
The head isn't a VERY great likness to Vermin in the comics, but I wouldn't be able to sculpt a better one myself, so...

The problem with the Werewolf figure is, though, that his head’s movement is very limited, making him always look down. This was a problem because I wanted Vermin to be more hunched over and creature like, so I took a neck-joint-thing, but instead of having the big wheel-like end in the neck, I put it in the head (see picture #2) so that he easily can bend over and still look straight in front of him.
I re-painted the whole figure, a few times actually for different reasons, and the end result came out very much like the colors the Werewolf body originally had. I might attempt to dry-brush a lighter brown color sometime. That could be nice.
I also see now that I’ve forgotten to paint the nails on his hands and feet! How annoying!

Anyways, it’s a pretty nice figure and I now have Vermin on my Spider-Man shelf!