A Class 9 entity is a special classification used in some video games and used once but not in the primary canon.
Primary Canon
No entities have been classified a Class 9.
Secondary Canon
Ghostbusters: The Video Game
List of Entities
Ghostbusters: Spirits Unleashed
List of Entities
Animated Series Class 9
The animated series doesn't follow the same rules as RPG and can go higher. To read more about it go to Animated Classifications.