Stay Puft Marshmallow Man is a former enemy turned ally to the Ghostbusters (mainly Slimer, as it seems he really is the only one he listens to, even though in "Sticky Business", he was shown to be angry when the Phantom stole the Ghostbusters' Proton Packs and even said the Ghostbusters were his friends). The Ghostbusters and Slimer often refer to him as "The Big Guy." He is the only ghost from both movies other than Slimer to receive a toy in the original Kenner toyline.
For more information of the movie version of this character go to the movie article.
At some point after the Gozer incident, the Stay Puft Marshmallow Man was captured and placed in the Containment Unit. The Stay Puft Marshmallow Man was accidentally released from the Containment Unit by Egon's skeptical uncle Cyrus. Stay Puft was antagonistic and once again rampaged in the city before the Ghostbusters managed to retrap him. They used four to five Traps to capture it after they tripped it with a cable strapped to Ecto-1.   Some time later, the Ghostbusters reluctantly released him to fight a giant monster taking the form of Murray the Mantis that had been spawned from a possessed Thanksgiving Day Parade balloon. Despite the reservations of the city authorities, Peter assured them that Stay Puft was "all better now" suggesting some rehabilitation had occurred. After defeating the Mantis, Stay Puft took his place in the Thanksgiving Day Parade.
Other than the Episode "Cry Uncle", the pilot, and the intro of the show, The Stay Puft was a kind giant and the Ghostbusters seemed to like him and worked with him in two episodes "Sticky Business", and "The Revenge of Murray the Mantis". He seems to respect and later in the series like the Ghostbusters, to the extent that he once states all of them are his friends.  He can be very child friendly as shown in "Sticky Business" but is a free spirit still.
The Stay Puft Marshmallow Man's appearances in the animated series appears to be contradicting the events of the original film. No explanation is offered as to how Mr. Stay Puft, originally the incarnation of Gozer, became an entity in his own right. There have been many theories, one of the most likely ones being that another entity entirely decided to take on the form of Mr. Stay Puft itself. It was also commonly speculated the remains of the original Marshmallow Man were collected using the ghost traps and stored in the Containment Unit, where he regenerated back to his original form.
Mr. Stay Puft makes a brief cameo as an antagonist in the original opening sequence, only to be trapped with a bunch of other ghosts. That may not be canon at all as the intro seems to be inconsistent with how ghostbusting is done in the cartoon episodes.
In "Cry Uncle" Stay Puft was released and was deemed a malevolent ghost. It could have been a mistake by the writer or maybe J. Michael Straczynski, Story Editor, changed his feelings on Stay Puft. Also worth noting that he was released in a very odd way, in small form from the middle of the Containment Unit machine and not from the trapdoor device on the front bottom level of the Containment Unit.
Stay Puft's vocabulary is inconsistent throughout the series. In "Cry Uncle" and "The Revenge of Murray the Mantis", he could not speak and communicated with grunts and growls. This was contradicted in the episodes "Deadcon 1" and "Sticky Business" when he was shown to be able to speak fluent English. On another note, in "Sticky Business", it was inconsistent on Stay Puft's grammar. Some of the sentences he said had perfect grammar (such as "I don't like being stuck") and some did not (such as "Me hate Phantom. He bad dude!")
One theory on how Stay Puft came back to "life" and how he came inside the Ecto-Containment Facility is as follows.
After Gozer's defeat the Ghostbusters collated all the ectoplasmic marshmallow leftovers of Stay Puft and store it inside the newly constructed Ecto-Contaiment Facility and that without Gozer’s influence to control his actions, Stay Puft “pulled” himself back together and became the kind-hearted marshmallow giant we all know and love. (Popular Explanation)
A simpler, more likely explanation would be that another entity simply took on the form of Mr. Stay-Puft independently of Gozer. Stay-Puft marshmallows are apparently a prominent, popular dessert item with lots of media exposure. The big guy in the cartoon doesn't appear terribly smart or for that matter, creative and could have taken the form because he witnessed Gozer using it and wanted to emulate him.
The Real Ghostbusters PilotEdit
- The Real Ghostbusters Pilot
- Appears as a villain. Surprisingly, Slimer is seen eating Stay Puft Marshmallows and Ray Stantz is sleeping with a doll of Mr. Stay Puft earlier in the episode. Stay Puft grabs Peter and Ray, "saving" them from an incoming subway train. He smiles at the delight of holding them in his hand until a skeleton riding an airplane flies by and snatches them from him.
- As the pilot episode was created solely to pitch the idea to the producers to demonstrate how the series could look, it isn't to be regarded as part of any continuity.
The Real GhostbustersEdit
- The first introduction title sequence to the series and seems to be a villain.
- A doll of Stay Puft appears in many episodes being held by either Ray or Slimer.
- "Mr. Sandman, Dream Me a Dream"
- As a dream by a boy with a bag of Stay Puft Marshmallows.
- "Cry Uncle"
- As a villain mistakenly released by Cyrus Spengler.
- "Adventures in Slime and Space"
- "Ghost Busted"
- Cameo appearance and winked at the viewers at the end of the episode.
- "Apocalypse - - What, Now?"
- As an advertisement for Stay Puft Marshmallows on the TV screen during the Special Report.
- "Deadcon 1"
- Appears in the episode as mistakenly being released, however, he is not a threat. He is Deadcon's guest of honor and at the end seems to have been left behind. The Ghostbusters remember Stay Puft while driving home.
- "The Revenge of Murray the Mantis"
- As an ally of the Ghostbusters. Got out of the Containment Unit to fight Murray the Mantis.
- Visually part of the Ecto-1 roller coaster.
- "Sticky Business"
- He is let out of the Containment so he can be used in a Stay Puft Marshmallows commercial. He later helps the Ghostbusters recapture the Phantom, who managed to get out of the grid by hiding under Stay Puft's collar.
- "Short Stuff"
- Ray mentioned Stay Puft. 
- "Partners in Slime"
- As a cameo in the Containment Unit playing with a yo-yo. He sees Slimer and greets him, but seems to be unaware that Slimer almost got hit by his yo-yo. He does not appear to have any ill feelings about being trapped in the Containment Unit.
- Prosecutor ghost shows the Ghostbusters a photo of Stay Puft
- "The Halloween Door"
- As a cameo in a scene where Boogaloo is dancing.
- "Deja Boo"
- In a flashback
- Title End Sequence of Season 6
- A reuse of the early season's introduction title sequence
- He has made several cameo appearances in issues of the comic book published by NOW Comics and the comic book published by Marvel Comics in the United Kingdom.
- Ghostbusters Volume 2 Issue #2
- In The Box Part Two
- Stay Puft Marshmallow Man never appeared nor was mentioned in Extreme Ghostbusters, making him the only ghost who was part of any Ghostbusters film to never once be referenced.
- On the subscription cover of Ghostbusters Volume 2 Issue #13, Stay Puft makes a non-canon cameo.
- On the subscription cover of Ghostbusters Volume 2 Issue #16, Stay Puft makes a non-canon cameo behind Ecto-1.
- On Page 7 of Ghostbusters Annual 2017, in panel 4, the lower half of Stay Puft makes a non-canon cameo.
- ↑ Egon Spengler (2009). The Real Ghostbusters - "Cry Uncle" (1987) (DVD ts. 19:15-19:18). Time Life Entertainment. Egon says: "He's too big for the Ghost Traps we have with us."
- ↑ Winston Zeddemore (2009). The Real Ghostbusters - "Cry Uncle" (1987) (DVD ts. 19:18-19:19). Time Life Entertainment. Winston says: "By themselves, yes."
- ↑ Peter Venkman (2009). The Real Ghostbusters - "The Revenge of Murray the Mantis" (1987) (DVD ts. 15:31-15:34). Time Life Entertainment. Peter says: "Yeah! And he's all better now. We think."
- ↑ Mayor Lenny (2009). The Real Ghostbusters - "Adventures in Slime and Space" (1987) (DVD ts. 11:51-11:55). Time Life Entertainment. Mayor says: "First, Terror Dogs. Then a walking marshmallow. Now this!"
- ↑ Ray Stantz (2009).The Real Ghostbusters- "Short Stuff" (1988) (DVD ts. 02:20-02:23). Time Life Entertainment. Ray says: "Remember the good old days? Stay Puft. The Sandman."