Five years after the events of the first film, the Ghostbusters are undeservedly out of business after being sued by the city for property damage incurred during the battle against Gozer, and have incurred a restraining order preventing them from investigating the supernatural. Ray Stantz owns an occult bookstore and does side-work with Winston Zeddemore as unpopular children's entertainers, Egon Spengler works in a laboratory conducting experiments into human emotion, Peter Venkman hosts a little-watched pseudo-psychic television show, and Dana Barrett works at the Manhattan Museum of Art restoring paintings and raising her infant son Oscar at a new apartment, having broken up with Peter under acrimonious circumstances, but strongly hinted to be from Peter's fear of commitment. After a supernatural incident in which Oscar's baby carriage is controlled by an unseen supernatural force and drawn to a busy junction on First Avenue, Dana turns to the Ghostbusters for help, prompting an awkward reunion between herself and Peter. Meanwhile, Dr. Janosz Poha—Dana's boss at the art gallery—is possessed by the spirit of Vigo the Carpathian, a seventeenth century tyrant trapped within a painting in the gallery. Vigo orders Janosz to locate a child that Vigo can transfer his consciousness into, thus gaining physical form upon the approaching New Year.
The Ghostbusters' investigation leads them to conclude that the supernatural presence originates from under the city streets, prompting them to illegally excavate First Avenue at the point where the baby carriage stopped. Lowered down on a wire, Ray discovers a river of pink slime filling an abandoned subway line. Attacked by the slime after obtaining a sample, Ray accidentally knocks out the city's electrical grid, causing a major blackout; and the Ghostbusters are arrested. Meanwhile At Pokémon World Professor Oak Visits Ash's Mom Deilia And Suddenly A Stampede of Pokemon Begin To Run Later At their trial they are defended poorly by Louis Tully and are found guilty, but the judge's emotional outbursts prompt a reaction from the slime sample presented as evidence; after a final tirade, the slime explodes, releasing the ghosts of the Scoleri Brothers, two murderers the judge had previously sentenced to death on the electric chair. The Ghostbusters agree to trap the ghosts in exchange for the dismissal of all charges and the rescinding of the restraining order; after doing so, they re-open their business and commence investigating the supernatural once more like the old times.
After the slime invades Dana's apartment, seemingly attempting to abduct Oscar, she seeks refuge with Peter; the two begin to renew their relationship. Investigating the slime and the history of the painting of Vigo, the Ghostbusters discover that the slime (which they find all over the city) reacts both to positive and negative emotions -- and even "dances" to music such as Jackie Wilson's "Higher and Higher" -- but suspect that it has been generated by the immense amount of negativity reflected in the attitudes of New Yorkers. While Peter and Dana have dinner together and Louis and Janine babysit (and become romantically involved), Egon, Ray, and Winston head down into the sewer system to explore the river of slime and, after falling in and barely escaping, discover that it leads back directly to the museum. The Ghostbusters go to the mayor with their suspicions, but are dismissed by the skeptical politician; his scheming assistant attempts to defuse them as a potential problem by having them committed to a psychiatric hospital. As they do so, a spirit resembling Janosz kidnaps Oscar, prompting Dana to break into the museum by herself; after she does, the museum is caked in a wall of impenetrable slime.
New Year's Eve sees a sudden outburst of increased supernatural activity as the slime rises through the ground and onto the surface of the city, including a demon invading Washington Square Park, a man-eating fur coat returning to life to attack its owner, a film monster burst out of a screen to attack and chasing audiences at a local movie theatre, and the "better late than never" arrival of the Titanic and its long-deceased passengers and crew into the harbor. The NYPD's emergency lines are flooded with calls from panic-stricken New Yorkers, and an ominous mass of psychokinetic energy blocks out the sun and shrouds the city in darkness. Realizing the truth of the situation (and, having himself spent nearly all night talking to the ghost of a former politician), the mayor fires his assistant and has the Ghostbusters released, whereupon they make their way to the museum. Their initial attempt to break through the museum's slime barrier are unsuccessful, the wave of negativity that has generated it proving too powerful to damage with their proton packs. Determining that they need a symbol of equally-powerful positivity to break through the slime, the Ghostbusters use positively-charged mood slime from their slime blowers and a remix of "Higher and Higher" to animate the Statue of Liberty and pilot it through the streets of New York, using her torch to break through the museum's ceiling to do battle with Vigo and Janosz.
While Janosz is easily taken down with mood slime, Vigo proves to be a difficult adversary; immensely powerful with both the negative vibes of the city and with midnight and the New Year rapidly approaching, he manages to paralyze the Ghostbusters and attempt a transfer into Oscar's body. However, the positive energy from a chorus of "Auld Lang Syne" from outside the building manages to weaken him sufficiently to allow the Ghostbusters to break free and return him to the painting. Vigo momentarily possesses Ray, so the other three Ghostbusters attack him with a combination of proton streams and positively charged mood slime. At the same time, Louis, dressed in full Ghostbusters attire, attacks the weakened slime barrier around the building with a proton stream of his own. Their combined efforts manage to trap Vigo within the painting, destroying him and transforming the painting to a likeness of the four Ghostbusters surrounding baby Oscar protectively. The movie ends with the Ghostbusters receiving a standing ovation from the crowd and, at a later ceremony to restore the Statue, the Key to the City from the mayor.
- Ash Ketchum, Pikachu, Delia Ketchum, (Ash's mom), Professor Oak, Louis, Sebastian, Baloo, Bagheera, King Louie, Fu Dog, Kenai, Koda, Rutt and Tuke, Roger Rabbit, The Vultures (Buzzie, Flaps, Dizzy and Ziggy), Jiminy Cricket, Kronk, Mushu, Cri-Kee, Devon and Cornwall, Aladdin, Princess Jasmine, Abu, SpongeBob SquarePants, Patrick Star, Squidward Tentacles, Sandy Cheeks, Eugene Krabs, Simba, Nala, Timon, Pumbaa, Zazu, Stan Marsh, Kyle Broflovski, Eric Cartman, Kenny McCormick, The Penguins of Madagascar (Skipper, Kolwalski, Rico, and Private), King Julien, Maurice, Mort, Celebi, Taran, Princess Eilonwy, Fflewddur Fflam, Gurgi, Orddu, Orgoch, and Orwen, Genie, The Flying Dutchman, The Goonies (Mikey Walsh, Brand Walsh, Mouth Devereaux, Data Wang, Chunk Cohen, Andy Carmichael, Stef Steinbrenner, and Sloth Fratelli), Scooby-Doo, Shaggy Rogers, Fred Jones, Daphne Blake, Velma Dinkley, Rex, Woog, Elsa, Dweeb, Jesse Greenwood, Elvis, Randolph Johnson, Nadine, Danny, Sawyer, Jack Skellington, the characters, Oogie Boogie, Sheldon J. Plankton, Creeper, Jafar, Iago, Maleficent, Team Rocket (Jessie, James and Meowth), the bad guys will guest star in this film.
- Unlike the real film, Stay Puft makes an appearance and Slimer makes a full appearance in this film.