The Ghost is a Monster kept in the Facility. It was not listed on the whiteboard, nor was it seen during the System Purge.
Physical Description and Attributes[]
The Ghost appears as a very faint, but dark, silhouette of what the audience can presume is a humanoid. It is similar to the Creeping Shadow in that the two Monsters are mostly transparent and are hard to distinguish from their surroundings. Other descriptors of the Ghost are unknown since it can only very faintly seen once in the film. Other lore surrounding the Ghost or why it was captured by the Facility are unknown.
The item that summons the ghost from Cabin's Cellar is unknown. Possibilities include ghost hunting equipment, Ouija/spirit boards or a supernatural artifact or object.
Appearances[]
The Ghost's only appearance is briefly seen behind the Sugarplum Fairy's cube during the cube scene when the camera pans out to reveal all of the cube prisons.
Inspiration[]
There are thousands of horror themes including ghosts and spirits, both benevolent and malevolent. The Ghost could very well just be a Monster created to fill one of the cube prisons by the developers and have no direct reference at all.