It's strictly fictional. The story and characters in 'Mom of Monsters' are the product of the author's imagination and not rooted in any actual occurrences.
The characteristics can be quite diverse. Consider the Jersey Devil. It has features like hooves and a horse - like head which could be related to the rural, farming areas where it was first sighted. The wings might be added because of the mystery of flight. These monsters are often a product of people trying to explain strange happenings. So, their characteristics are a combination of what people saw or thought they saw, and their own cultural and superstitious beliefs.
Monsters Inc is not based on a true story. It's a highly imaginative concept developed by the creative minds at Pixar. The idea of a factory full of monsters and a parallel world where they live and operate is a product of pure fantasy. There's no real - life basis for things like the monster characters, the scream - energy concept, or the door - traveling system in our world.