In When Halloween Was Forever, when ancient ruins arrive in New York for examination, the evil spirit of Samhain is released! He declares that Halloween should last forever and calls forth an army of the night! 
A UBN News van pulled up to where Ecto-1 was parked. Cynthia Crawford quickly started the report and stated it was hours before Halloween Eve started. Inside the building, the Ghostbusters are on the job and trapped several hairy ghosts. As Crawford quoted Peter Venkman, the weakened door falls down. The weary Ghostbusters marched out with one smoking Trap each. Peter stopped for an interview and denied any difficulty during the job. They then headed back to their headquarters and Peter noticed Egon is in deep research. Winston wonders why the job was so hard. Ray wondered if it had to do with Halloween approaching. Peter asked what was going on, but Egon refused to tell him. Peter then threatened Egon saying that he'll tell Slimer there is a cupcake in his sock, Egon then tells him he suspects that the large increase in P.K.E. readings centers around ancient ruins that were brought in from Ireland two weeks ago. They date back to the seventh century. Ray and Egon begin to notice a connection between the ruins and the origins of Halloween. Winston suggested they investigate but Peter is nonchalant about it.
After Peter turned his back, Egon told Slimer that there was a lollipop in Peter's sock and Slimer attempts to find it. Meanwhile, two goblins sneak into the museum, chanting "Samhain." They then draw an infinity symbol on the ancient clock from Ireland, unleashing the ghost Samhain. Samhain then flew off to gather minions of the night while the goblins head out on the town. The goblins then come to the Ghostbuster headquarters and blow Janine against the wall. Upon hearing her scream, the Ghostbusters suit up and head out, where they start trapping the various ghosts in the town. The P.K.E. Meter went right off the scale and a city-wide manifestation overcame New York.
Slimer meanwhile is at the headquarters and starts to hear a ghostly voice. Slimer is then dragged out of the building and brought to a gathering of ghosts, who are all listening to Samhain who says there is much to do tonight. Slimer is then brought to Samhain, who smells the Ghostbusters stench on him. Disgusted by the smell of humans, Samhain tells Slimer he will join his midnight army or pay the price.
Meanwhile, the Ghostbusters have just captured another ghost and noticed that their watches haven't moved despite hours of catching ghosts. Samhain then appeared before the Ghostbusters and asked them why they are harming his "little ones." When Peter says they've been catching them for hours, Samhain shoots a black lighting bolt at him. Samhain then introduces himself and Ray says that Halloween began as the feast of Samhain, a creature of the night who none could stop (Samhain then comments how it is good that he is remembered). Peter then asked when he's leaving, to which Samhain says he is not. Samhain then revealed that he has halted time, to make it an eternal Halloween night. Egon then shines a flashlight on him and Samhain fled to another building where he is joined by his many ghosts. The Ghostbusters the decide to use the lights in the city against him, only to find the lights are going out.
Egon then comes up with a plan and tells Peter, Winston and Ray to distract Samhain with a frontal assault. Meanwhile, Slimer is up on the building after being forced into joining the crowd. Samhain tells Slimer he has more in common with him than the Ghostbusters, to which Slimer spits at him. The other ghosts seize Slimer, but Samhain says to stop as he may prove useful. Meanwhile, Egon uses two ghosts driving a car to move some spotlights into place, then he hooks up his pack to the lights to charge them. Peter, Ray and Winston reach the top of the building and come face to face with Samhain. Samhain then pulls out a weakened Slimer and orders the Ghostbusters to lie down their weapons. Samhain then starts to stroke Slimer, preventing him from getting free. However, Slimer breaks away after Ray screams "Pizza!" Egon turns on the spotlights and Samhain is then stunned and is captured in a Trap with the rest of the ghosts.
Back at the Firehouse, Winston empties the Trap as the other Ghostbusters watch Samhain sit in the Containment Unit waiting. Janine then turns out the lights and dresses Slimer in a pumpkin (causing him to look like a floating pumpkin). After the Ghostbusters see the truth behind the trick, they play a tickle trick on Janine (which she happily laughs at).
- Peter: (grabs Slimer) "Now hold real still, okay? (to Egon) Now Egon, either you tell me what you're working on, or I'll tell Slimer you're hiding a cupcake in your socks!"
Egon: "You wouldn't dare."
Peter: "Why Egon, what's that in your socks? If I didn't know any better, I'd swear it looked just like a-"
Egon: (shoos Slimer away) "Okay okay I'll talk! I was just working out the minor details."
Peter: (tosses a lollipop which Slimer goes for) "Who says blackmail's a lost art?"
- Peter: "Egon, you little scrapper! I bet you know what's going on! Let us in, okay?"
Egon: "Okay. One: Halloween started to celebrate night's creatures. Two: suddenly, we're up to our hips in them. Three: night's fallen everywhere. Four: time is slowing down. Conclusion: it will be Halloween forever. This night will never end."
Peter: "Actually, I think I liked not knowing a lot better..."
- This episode is the first of three Halloween based episodes and the debut of the villain Samhain. The second Halloween based episode was "Halloween II 1/2" (featuring the return of Samhain) and the third was "The Halloween Door" (which Samhain didn't appear in).
- This is one of two episodes to have reporter Cynthia Crawford. She later is in the episode "Citizen Ghost".
- When prompted Egon thought he and Ray were building a Spectral Differentializer. 
- This device is finally used in "Adventures in Slime and Space."
- As Egon and Ray confer on what they are building, Winston was playing Checkers with Slimer.
- Janine gave the two goblins bon-bons.
- Peter quotes the much used "It was quiet. Too quiet" trope. 
- Winston refers to the Proton Packs as "Power Packs" when he confirms that they still work after the blackout.
- Just like the rest of the episodes of season it uses a track from The Real Ghostbusters Soundtrack. This episode features the song "Midnight Action" in part of the episode.
- This is the first time the Ghostbusters are seen using the viewer to look at the universe inside the Containment Unit.
- On page 14 of Ghostbusters International #10, in panel 2, on the bottom screen, is the news anchor dressed as a clown from "When Halloween was Forever."
- On page 2 of Ghostbusters Annual 2018, in panel 3, carved atop the pedestal is the Wheel of the Year. One circle represents life and the other represents death. Joined, they become infinity. In "When Halloween Was Forever", the two goblins released Samhain with the symbol.
- On page 10 of Annual 2018, In panel 5, right of Jenny Moran on the counter is a miniature of the relic Samhain was freed from in "When Halloween Was Forever".
- On page 21 of Annual 2018, the ghosts are visually based on Samhain's Midnight Army in "When Halloween Was Forever".
- On page 30 of Annual 2018, once again, the ghosts are based on Samhain's Midnight Army from "When Halloween Was Forever".
- On page 31 of Annual 2018, in panel 1 are the two 'Zone Dweebies' goblins in their car from "When Halloween Was Forever"
- On page 35 of Annual 2018, in panel 2, is a ghost from the end of "When Halloween Was Forever" when they look for Samhain in the Containment Unit, it is the last ghost but originally pink.
- ↑ Eatock, James & Mangels, Andy (2008). The Real Ghostbusters Complete Collection booklet, p. 4. CPT Holdings, Inc.
- ↑ Egon Spengler (2009). The Real Ghostbusters - "When Halloween Was Forever" (1986) (DVD ts. 06:44-06:45). Time Life Entertainment. Egon says: "A Spectral Differentializer."
- ↑ Peter Venkman (2009). The Real Ghostbusters - "When Halloween Was Forever" (1986) (DVD ts. 13:04-13:08). Time Life Entertainment. Peter says: "It was quiet. Too quiet. I always wanted to say that."
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|Mr. Sandman, Dream Me a Dream||Air Date||Look Homeward, Ray|
|Mr. Sandman, Dream Me a Dream||DVD Order||Look Homeward, Ray|