The Stay Puft Marshmallow Man or Mr. Stay Puft (also nicknamed 'Tubby Soft-Squeeze' by Ray and Peter) was the final enemy of the Ghostbusters in the first film. He was the chosen form of Gozer, when Ray let the idea of a company logo "just pop in there".
The Ghostbusters were told to choose the form of their destructor, and Ray "chose" him as the form. All the other guys claimed they had emptied their minds, but Ray said he tried to think of something that could never harm them. As a child, Ray used to roast Stay Puft marshmallows on the fire at Camp Waconda. The Stay Puft Marshmallow Man was simply the mascot for the Stay Puft brand. His accidental choice resulted in Gozer being manifest in the form of a 100-foot tall homicidal marshmallow man bent on destroying the Ghostbusters and New York. "Nice thinking, Ray" - Venkman.
Stay Puft stepped on a church before trying to scale 55 Central Park West building. After they tried to blast him with their proton packs, Stay Puft flamed up and nearly burned the Ghostbusters. The guys then decided to cross the streams to transfer the energy flow through the portal and when they did this, Stay Puft melted, spilling marshmallow all over the street, hitting thousands of passerbys, with one glob landing straight on Walter Peck.
While he didn't return in Ghostbusters II he was alluded to in the beginning after Ray Stantz and Winston Zeddemore attended a boy's birthday party. He also made a cameo in the video game based on the movie as a billboard advertising Stay Puft marshmallows in the Statue of Liberty level.
Ghostbusters: The Video Game
He appears again as a boss in the Ghostbusters: The Video Game, just as he did before. However, his limbs seem to have grown out a little since his appearance in the first movie, appearing less 'stubby' as a result. Due to Cult of Gozer's manipulations with the Mandala, the Destroyer god, Gozer, was able to re-manifest in our world again. And again, in the form of Stay Puft Marshmallow Man, this time rampaging through Times Square. Ray wonders why Gozer assumed the form of the Marshmallow Man again, as there are surely more effective world-destroying forms he could have taken. Ray ends up theorizing that there's "one destructor form per god per dimension", meaning Gozer can only assume this form in Earth's dimension. It is identified as a Class VII Outsider Avatar and a Deity (a supreme being). Because of complications Gozer faced penetrating the human realm, the Destructor Form was not even as powerful as his original incarnation, which would seem to be confirmed by him eventually being overcome by the firepower of a single Ghostbuster, Rookie, who used the Boson Dart, a new feature added to the proton pack, against the god. Stay Puft being weaker than he was before may also explain why the Ghostbusters originally planned to trap him in Ecto-1b's Super Slammer Muon Trap.
He demonstrated a new power, to spawn numerous Stay Puft Minis, a minor Marshmallow minions of him. Gozer tried to capture Ilyssa Selwyn in order to sacrifice her and make himself stronger, but ultimately failed. Not able to reach its full potential, the Stay Puft Destructor Form was destroyed, covering all the surrounding buildings and streets with hot marshmallow shower. Its giant hat also fell down on a building, where it is last seen hanging.
Secondary Canon History
The Real Ghostbusters
After his apparent destruction as Gozer's chosen form, Stay Puft became a good guy and made a few appearances in the animated series (even though being evil in non-canon pilot). He was in the intro of the first season, he was dreamed up from a sleeping little boy, and he helped the Ghostbusters fight evil ghosts occasionally. Stay Puft was eventually dropped in later seasons. He never appeared on Extreme Ghostbusters.
It should probably be noted that the animated series were either unaware or chose to ignore the fact that the Marshmallow Man was a manifestation of Gozer. The series seemed to treat them as separate beings.
For more information of the animated version of this character go to the animated article.
Ghostbusters: Sanctum of Slime
There are 30 items to collect in the game. They are all modeled after the Stay Puft Marshmallow Man.
After the Shandor incident, the Ghostbusters encountered Stay Puft again. They managed to disperse enough of his P.K.E. to stunt reformation and spectral mitosis then used multiple Ghost Traps to capture most of Gozer's essence. It was then stored in the Containment Unit.  
During the events of the Infestation, a new type of Poltergeists with a different energy signature from typical entities escape from the Containment Unit. During the breach and unknown to the Ghostbusters, Gozer's essence escaped and Stay Puft Marshmallow Man reformed. Eventually, Ray is the one to discover this and informs the rest of the team. As news crews provide a live feed of Stay Puft's march on West 57th Street, all 37 remaining Zombies are routed by Britt to infect, and thus weaken, Stay Puft so she may complete her mission and capture a portion of Gozer's essence.
The Ghostbusters arrive and determine the best course of action is to attempt a massive ectoplasmic cross-pollination and inoculate Stay Puft with dozens of the recaptured Poltergeists. However, during this plan, Stay Puft literally tears himself apart and a zombie doppelganger is formed. Now weakened by the forced split, Stay Puft continues to fight. Concerned about the continued presence of Necrotic Slime, Egon Spengler urged the team to continue releasing Poltergeists. After the necrotic double was safely destroyed, Stay Puft's readings began to diminish. The split affected him on a molecular level and caused him to disperse. By Egon's calculations, Stay Puft will eventually reform then another uptick in supernatural activity will occur as his energies wander around Manhattan.
Months later, during a precognitive episode, Ray saw the Stay Puft Marshmallow Man but in his visage. Ray's Spirit Guide assured Ray it was good he felt responsible for Stay Puft. With the reformation of Stay Puft looming, Ray went to work and completed the Megatrap, designed to capture large entities in one shot. During the Re-Selection of Gozer's Destructor Form, the spirit guide influenced Ray first and had him think only of Stay Puft. Ray complied and Gozer manifested as Stay Puft once again. While the other Ghostbusters opened fire on him, Ray went downstairs with the Megatrap to room 2206. Ray held the Megatrap out a window and trapped enough of Gozer's essence to defeat Stay Puft. Without it, Stay Puft exploded. The residue covered one square mile with a depth of up to six inches, causing heavy utility damage and covering most of Central Park.
In Ghostbusters game for Sega Mega Drive, which is set between the movies (and which canon status is moot), Stay Puft appears again as a boss. However, this Stay Puft is not connected to Gozer in any way To Read more on Stay Puft in Ghostbusters Sega game, click here.
The Stay Puft Marshmallow Man is a Class 7 Outside Avatar (alternatively a Class 7 Avatar Manifestion in the Stylized Version of Ghostbusters: The Video Game) as evidenced when it was scanned during the Shandor Incident in 1991.
Originally, Stay Puft was believed to be a Deity (Supreme Being). In its Paranormal Contracts Oversight Commission file, Stay Puft is stated to be a psychokinetically charged and ectoplasmically animated gateway homunculus.  It was also stated with each formation, the Gozer energy signatures were accompanied by physical readings from Stay Puft. More and more latent psychokinetic energy was drawn into the creature to compensate for Gozer's deficiencies thus Stay Puft became more and more of a separate entity from Gozer. Potentially, being animated with energies without any kind of will makes Stay Puft more vulnerable to domination by intelligent powers other than Gozer. In theory, Class 5 ghosts and up, who are capable of animating physical mass and drawing latent P.K.E. from the environment could take control of Stay Puft.
- In the scene in Ghostbusters when Dana Barrett comes home from the grocer, one of the things in her bags are Stay Puft Marshmallows.
- In What in Samhain Just Happened?! on page nine, one of the party attendees is wearing a Stay Puft Marshmallow Man costume.
- As for the explanation of Stay Puft being in the Containment Unit preceding the events Ghostbusters: Infestation #1, writer Erik Burnham revealed "As to Stay Puft in containment? Well, I do have a "movie-ish" explanation for that that I didn't have the space to pop into this script, so I let it lie"  and "I promise, if I ever get to do GB again, I'll put Mr. Stay Puft back in and explain exactly how it works." 
- In Ghostbusters Issue #1's Ghostly Gallery, Erik Burnham writes Ray Puft was intended to both show Ray felt responsible for Stay Puft and foreshadow more of a link between the two. In the script, Ray Puft was described as Stay Puft with Ray's face. As the design went on, Burnham toyed with a radical amalgam of Ray Puft in a big blue jump suit but Dan Schoening's design convinced him simple was better.
- ↑ IDW Forums 1/23/12
- ↑ Erik Burnham confirms - IDW Forums 1/23/12
- ↑ Ghostbusters Issue #4, PCOC Pages
- ↑ "Countdown to Infestation..." on Ghostbusters Fans 3/13/11
- ↑ "Countdown to Infestation..." on Ghostbusters Fans 3/14/11
Secondary Canon Appearances
- IDW Comics