Eyeball is one of a number of ghosts that appear in the Subway at 21st Street in the Extreme Ghostbusters Intro. It has also appeared in episode "The Pied Piper of Manhattan" in the first scene and later in the city as one of ghosts causing havoc before Piper shows up. It appears in Heart of Darkness as both a Gateway ghost and a Spirit Slave. However, it was pink and not blue.
It appears to be floating one eyed ghost with some fish like behaviors and looks. It could be loosely modeled after a seahorse.
- Extreme Ghostbusters