Billy is Lily's brother who was supposedly expelled and never seen again. It is eventually revealed that he was kidnapped by the principal for walking in on the janitor disposing of one of the creatures' bodies. He was then placed in a container where experiments were conducted on him.
He is only seen after completing Lily's mission. His disappearance caused many students to distrust the school's faculty members. Any mention of Billy causes the Principal's Device to explode, killing the person who has it in their possession. You can also explode (with the device) the statue at recess for you to get the final Nugget of Friendship from Nugget.
Billy wears a ripped brown shirt, exposing some of his lower torso. He has black hair and seems to be queasy since he just escaped from being experimented on.
- He is one of the only characters in Kindergarten who never dies.
Billy reappears in Kindergarten 2, debuting in the mission "Things that go boom" as a major character.
He is hiding in the basement, behind a box, with Lily. They are spying on the new school and are also trying to get in the elevator to find the Missing Children.
He mainly appears the same as his appearance in Kindergarten but now wears a brown hoodie which can be collected alongside his test subject outfit as Costumes.