Boo

Mary Ella Gibbs (better known as Boo) is the Tritagonist of the sequel series Monsters United.

Personality
Boo is a toddler who is curious and naive. She can talk but has baby gibberish vocabulary, and little dialogue because she's two years old. The only actual words she says in the film are "Boo!", "Kitty!", and "Mike Wazowski!". In other ways, she is advanced for her age, such as already being potty trained. This is seen when she shows to Sulley that she needs to go to the bathroom and does not need any assistance.