Boney Boy is a top hat wearing human skeleton found in Ms. Murawski's science classroom. It was revealed in "Backward to School Night" that he is actually a real human skeleton when he turned into a living human upon being hit with the age regressor ray.
Boney Boy is an adult human skeleton completely bare of clothes save for a rather dapper looking black top-hat. He is propped up by a metal stand.
As a human, Boney Boy has light skin and short blond hair. He wears a red button-up shirt, a pair of blue jeans with a black belt and brown shoes.
In "Sunny Side Up", Milo swung on Boney boy's stand while he was cheering, accidentally knocking it into a giant brain, which flew across the classroom and destroyed the egg they needed for their science project.
In "Disaster of My Dreams", Zack asks Milo if he ever feels like they're being watched. Milo cheerfully notes that he does feel watched whenever they sit next to Boney Boy, to which Zack sarcastically responds 'that's not creepy'. In reality, Elliot was watching them through a grate in the ceiling.
In "Backward to School Night", baby Dakota hits Boney Boy with the age regressor ray, which decreases the chronological age of anything it hits. Upon being hit, Boney boy was suddenly transformed into a living human, who promptly cried 'I'm Alive!' in excitement.
“Hey, Milo. Ever get the feeling somebody's watching you?”
“Stay gold, Boney Boy!”