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.
I met a kid at a math competition who insisted that he was a robot. He told us all he was 11.8 years old, and he didn’t bend his elbows when he walked. He didn’t smile or laugh with the other kids, and just stayed to himself the whole time.
I only saw him that one day, but I can tell you he was fully committed to being a robot that day.