I had a couple classmates that pretended to be vampires back in elementary and middle school. They’d pretend their Koolaid was blood, complain about the sunlight, and bite their friends a lot. Not enough to draw blood, though. I haven’t kept up with most of them, but one guy is a teacher now. He seems pretty normal.
Not so much supernatural, but a few in the less socially-included clique thought of themselves as rats. Grew nails long, scurried about, and most weirdly - hung out and ate lunch in the bathroom. It went on for a few years, well into sixth form, and ended up requiring a prefect to patrol the bathrooms at breaktimes to make sure they weren’t up to anything.
Oddly enough, I haven’t heard anything about them in school-reunion-type chatter.