During a rare eclipse of the moon, a baby ghosts slips through a dimensional crack and becomes lost in New York. The Ghostbusters adopt the cute ghost, but soon hear reports of two other ghosts causing trouble around town.

An incredibly powerful evil animal demon escapes from his statue prison and turns the animals of New York City into fierce, aggressive, talking beasts that proceed to take over the city.

Egon and Slimer switch minds and the timing couldn't be worse, as an egomaniacal ghost named the Master of Shadows (William Marshall) wishes to test his wits against the brainy 'buster', and destroy New York if he fails to measure up.

After an almost deadly fall off the World Trade Center, Egon's fears start to get the better of him. So much so that the Boogeyman manages to tap into his fear and escape from his realm.

When Slimer hides a book of fairy tales under one of Egon's newest machines, everything in the book comes to life.

An ectoplasmic entity leaks out of the containment unit and it makes Slimer mutate into a big ugly monster during his sleep.

The Ghostbusters release the Stay Puft Marshmallow Man from the containment unit to shoot a commercial in exchange for getting $50,000 for a children's hospital. However, during the process of letting Stay Puft out, a vicious manta ray-like phantom escapes in order to seek revenge against the Ghostbusters.

Samhain's goblins release the spirit of Halloween from the Ecto-Containment Unit, and he turns the firehouse into his fortress. The Ghostbusters' attempts to take him down are foiled when the Junior Ghostbusters are captured by the vengeful spirit, and it's up to Slimer to help get them out.

A boy named Lee goes to the Ghostbusters for help when his brother, Alec, begins acting strangely and doing bad things. When the guys decide to investigate, Egon learns a Grundel is making Alec do bad things and if something is not done soon, he will mutate into one.

The Ghostbusters' old "pal" and nemesis, Walter J. Peck, ex-EPA hatchet man extraordinaire, is back from the Gozer incident, and he's trying to raise some trouble with the Ghostbusters again. First he tries to get them arrested for illegal trespassing by calling in a phony ghost alert at a military base in Queens, but after that backfires, Peck joins up with BUFO (Bureau of Unidentified Flying Organisms), and takes Slimer with a court order. After some tests, Peck deems Slimer a hazard case and plans to destroy him with a cyclotron, forcing Ghostbusters to save Slimer from Peck.

The Ghostbusters have to deal with a shapeshifter in their own headquarters.

The Ghostbusters embark on a camping trip, only to run into (among other things) Bigfoot.