When the Ghostbusters return from a job at a dynamite factory, Slimer is grumpy because they couldn't bring him along. The Ghostbusters try to cheer him up, but fail, then empty the traps. They note that the outside of the containment area has been making strange noises, but they're too tired to investigate them, so they go to bed.
Slimer is still mad at the Ghostbusters, so he doesn't sleep in the bedroom, instead sleeping in the hallway. He dreams that he's a Ghostbuster and saves the guys, then some odd gas leaks from the containment unit, which Slimer inhales. Then, he flies away.
Janine gets a call and sends the Ghostbusters to a deli, which is being haunted by a large, messy, ravenous, green ghost. They manage to chase it away, but not trap it, then they go home to find Slimer back asleep, now in the bedroom. The guys notice the leak in the containment unit, but note that it wasn't big enough for any ghosts to escape. The next day, Peter tries to wake Slimer, but he's still sulking about not going on the mission, is lethargic, and is colder to the touch than usual. Peter wonders if something is wrong with Slimer and offers him chicken soup, then Slimer flies off in a trance.
The Ghostbusters then get called to a restaurant on a harbour, haunted by the same green ghost from before. Once again, they fail to catch it, then later, Slimer turns into the evil ghost. Egon, meanwhile, fixes the leak in the containment unit and reveals that the gas was "catalytic paranormal flux", which was harmless to living entities, but could turn ghosts "mean and ugly". Evil Slimer enters, and the guys trap him, but then they trip on his ectoplasm, drop the trap, and Slimer escapes. He reverts to his normal form, which makes the Ghostbusters realise they've been hunting Slimer.
Egon realises that the paranormal flux must have affected Slimer, and that if he transforms too many times, he'd be stuck in his evil form. Since he only transforms in his sleep, Peter and Winston try to keep Slimer awake while Egon and Ray search for a cure. Egon eventually gives up hope, and to make matters worse, Slimer transforms again.
The Ghostbusters chase Evil Slimer to a supermarket, where Egon gets the idea to separate the two personas using a different setting on the proton packs. After a bit of a struggle, they do this, and they trap Evil Slimer.
This episode provides examples of
- Badass in Distress: In Slimer's dream, the Ghostbusters need rescuing from him.
- Balloon Belly: At the end, Slimer gets fat after eating many popsicles (perhaps because he's a ghost).
- Beauty Equals Goodness: Downplayed. While Slimer isn't usually very pretty at the best of times, Evil Slimer is even uglier — he has horns, long pointy fingernails, jagged teeth, and is a sickly, dark green (like algae).
- Blowing a Raspberry:
- Slimer blows a raspberry to the Ghostbusters at bedtime.
- Evil Slimer blows a raspberry in the delicatessen.
- Bullying a Dragon: Evil Slimer blows a raspberry at the Ghostbusters even though they're wearing proton packs.
- Comfort Food: When Slimer is angry, Peter tries cheering him up with a candy bar.
- Comically Missing the Point: When Peter says he will search the frozen food department for Evil Slimer, Egon gets the idea of separating him from the regular Slimer and says, "That's it." Peter says, "The frozen food department?".
- Covered in Gunge: Evil Slimer gets ectoplasm all over Peter twice.
- Dramatic Irony: The Ghostbusters claim that the leak in the containment grid didn't do any damage, even after it's been revealed to the audience that Slimer is the evil ghost.
- Dream Sue: At one point, Slimer dreams that he becomes a Ghostbuster himself and saves the guys from a monster.
- Ectoplasm: Evil Slimer gets thick, green slime all over the walls and floor, and on Peter.
- Evil Laugh: At one point, Evil Slimer laughs evilly.
- Foreshadowing: There are several hints that the evil ghost is Slimer before he's actually seen transforming:
- He's a Big Eater, is green, and leaves ectoplasm everywhere, just like Slimer usually does.
- When Slimer flew out the window, he seemed to be in a trance.
- Slimer breathed in the gas that leaked from the containment unit.
- Slimer seemed sleepy in the morning (because he'd stayed up late in his evil form) and was colder than usual.
- Heel–Face Revolving Door: Due to the "catalytic paranormal flux", Slimer keeps reverting from good to evil and back again.
- I'm Cold... So Cold...: According to Peter, Slimer usually feels cold, which fits with him being a ghost.
- Involuntary Shapeshifting: Due to breathing in the "catalytic paranormal flux", Slimer turns into a brutish, ugly version of himself whenever he falls asleep.
- Pun: Venkman describes the job at the dynamite factory as "a blast".
- Mythology Gag:
- Slimer is called a "spud" several times, which references Ray's line from Ghostbusters (1984) about "He's an ugly little spud".
- When Evil Slimer gets ectoplasm on Peter, the latter says, "He slimed me!", which is what he said in the film.
- Platonic Declaration of Love: Ray says, "I love you" to Slimer at the beginning.
- The Pratfall: When the Ghostbusters trip on Evil Slimer's slime, Peter and Ray fall on their behinds.
- Scary Teeth: Evil Slimer has jagged teeth.
- Slapstick: The Ghostbusters' pursuit of Evil Slimer results in things like them tripping on his slime, getting covered in soot, etc.
- Sleep Deprivation:
- When Peter wakes up Slimer to do his chores, Slimer is still sleepy because he'd stayed up late in his evil form.
- Slimer becomes very groggy late in the episode due to the guys keeping him awake so he won't morph into Evil Slimer.
- Soup Is Medicine: When Venkman thinks Slimer is sick, he offers him chicken soup.
- Speak in Unison: The Ghostbusters say, "Slimer?!" when it's revealed that he was the one they'd been chasing.
- Stock Animal Diet: A cat is seen carrying a fish skeleton in its mouth.
- Tempting Fate: When Egon is giving up hope, Ray tells him that he's sure something good will happen... right before Slimer morphs into Evil Slimer again. (Though, something good does happen later).
- Unwitting Instigator of Doom: Slimer's mishap was partly the fault of the Ghostbusters (for not identifying and fixing the leak sooner) and also partly the fault of Slimer himself (for sleeping too near the containment unit).
