In the Netherworld, a Slimer-like ghost steals the lollipop of a ghost resembling a little boy. The ghost boy's three older brothers arrive and corner the Slimer doppelganger, but he tricks them into looking away and escapes. Meanwhile, Louis and Slimer are trying to play Blackjack, but Slimer takes "hit me" literally. Janine comes back with an antique mirror she brought from a garage sale, but the mirror turns out to contain a portal to the Netherworld, which Slimer's evil twin looks out of.
While Janine goes to the bathroom, the evil twin enters the firehouse through the mirror. When she comes back, she sees ectoplasm on the mirror, assumes Slimer did it, and yells at him to clean up. While he washes the mirror, the evil twin enters the kitchen, attacks him, and tries to force him through the mirror. He then throws both Slimer and Louis through the mirror, spray-paints it black, and throws it into a garbage truck. In the Netherworld, the older brother ghosts mistake Slimer for the evil twin. Louis tries to defend Slimer, but the other ghosts don't believe him, so they run away.
Peter and Egon arrive back at the firehouse (Ray and Winston are on a separate job) and Peter looks for Louis so he can do taxes. He finds a mess in the kitchen, assumes Slimer made it, and yells at the doppelganger (who he thinks is Slimer) to clean up. The twin obeys, and pretends he has a cold to make an excuse for his deeper voice. When Peter leaves, the Slimer double stops cleaning and flies into the living room, then turns up the TV. Egon tells him to turn the TV down so he can read, but the evil twin just screams at him. Peter checks the security cameras for Louis and sees footage of the double, so he and Egon trap the double.
Peter, Egon, and Janine drive to the dump and try to track down the mirror with PKE meters. Meanwhile, Louis and Slimer have outrun the brother ghosts, but have found a demon. When Egon finds the mirror in a pile of garbage, Louis and Slimer ask for directions at an information desk. They board a bus, but are launched out of it, then they meet the three brother ghosts again. Janine finds the mirror, Egon wipes the paint off, and Slimer flies through the gateway, while Peter reaches in and pulls Louis out. The mirror then falls to the ground, and Egon determines the portal is closed. They go back home and play Blackjack again.
This episode provides examples of
- Baguette Beatdown: When Slimer takes "hit me" too literally, he hits Louis with a sub made from a baguette.
- Be Careful What You Wish For: Louis wants the bus to go faster, but then the bus goes so fast, that he and Slimer are launched out the window.
- Blowing a Raspberry: The Slimer lookalike blows a raspberry at the little ghost.
- Covered in Gunge: Egon and Peter return to the firehouse with ectoplasm all over them.
- Cyclops: The demon Louis and Slimer encounter has one huge eye.
- A Day in the Limelight: Louis and Slimer get more focus than usual.
- Distressed Dude: Louis and Slimer get trapped in the Netherworld and chased by ghosts and a demon.
- Does Not Like Spam: Discussed when Slimer's doppelganger tries to lie about taking the lollipop by pretending he doesn't like them.
- Ectoplasm:
- The evil twin leaves ectoplasm on the mirror, angering Janine.
- When Peter and Egon arrive, they're covered in ectoplasm.
- Evil Doppelgänger: The main villain of the episode is a ghost who looks just like Slimer, but is evil.
- Evil Is Petty: The Slimer doppelganger likes to do petty things like steal lollipops and turn the TV up too loud.
- Evil Sounds Deep: Slimer's double, plus the three evil ghost brothers, have deep voices.
- Friendly Ghost: Discussed when Louis hopes the Netherworld ghosts are friendly. The ones he and Slimer encounter are not, though the little boy ghost never does anything wrong.
- Green and Mean: The evil ghost is Slimer's lookalike, so naturally he's green.
- Instantly Proven Wrong: Upon arriving in the Netherworld, Louis wonders if maybe the ghosts are friendly... but then the ghost brothers confront him and Slimer.
- Leaning on the Fourth Wall: Slimer says, "Who you gonna call?" towards the end.
- Lost Food Grievance: The child-like ghost cries when his lollipop is stolen.
- Magic Mirror: The mirror contains a Netherworld portal.
- Mistaken Identity: The three Netherworld ghosts mistake Slimer for his lookalike, while the Ghostbusters initially mistake the lookalike for Slimer.
- Mythology Gag: Slimer gets called a "spud", referencing him being called one in the movie.
- Not Me This Time: Usually, it is Slimer who leaves ectoplasm and makes messes in the kitchen, but this time, despite Janine and Peter thinking it was him, it was his double.
- Ocular Gushers: When the boy ghost cries, his tears spray out like a sprinkler.
- Oh, Crap!: Louis and Slimer gain scared expressions when they see the one-eyed demon.
- Playing Sick: When Peter asks Slimer's double, who he thinks is the real Slimer, if he has a cold because his voice is deeper, the evil twin lies that he does have one.
- Quaking with Fear: Louis and Slimer shake fearfully when they encounter the three ghosts.
- Say My Name: Both Janine and Peter yell Slimer's name angrily when they discover messes his double made.
- Sure, Let's Go with That: When Peter asks Slimer's doppelganger, "What's with your voice? Do you have a cold?", the evil doppelganger agrees.
- Terms of Endangerment: The brother ghosts threaten Slimer by calling him "pal".
- Tooth Fairy: Discussed when Peter quips that he's not sure how he'll explain his shredded pillow to the Tooth Fairy.
- Unwitting Instigator of Doom: Janine bought the mirror, not knowing that it contained a portal to the Netherworld.
