The Doomsday Door in the episode Knock, Knock is actually a Containment UnitThe Ghostbuster themselves seem to have no other manner of getting rid of ghosts other than putting them into the Containment Unit and on various occasions there have been the problem of what happens when all the ghosts get out of the Containment Unit at once and it's not too dissimilar from what happened with this door. It seems like the Containment Unit would have to be kept intact for the rest of time, leaving a problem of how to warn future civilisations. It's a problem that comes up in nuclear waste disposal and it seems to come up with the warning stone and the door itself which says "Do not open until doomsday"
The Stay-Puft Marshmallow Man was recreated inside the Containment UnitThe Ghostbusters never "caught" him in any normal sense, but he's inside the containment unit in the cartoon, and somehow he's turned friendly now that, according to Ray, he's not being controlled by Gozer. But how's that possible, and when did it happen? Well, the Destructor was formed by all the PKE energy Gozer had gathered in New York and, when Gozer was dispelled, that energy got released again (causing Stay-Puft's physical form to collapse into marshmallow goop). Then that shapeless PKE energy gradually spawned dozens of individual ghosts, which the ghostbusters hunted down and caught in separate cases over the next several months. Once the last ghost was captured and sent into the containment unit with the others, they all merged back together into the Stay-Puft Marshmallow Man... except, without Gozer's influence, he now has the same friendly personality that Ray imagined he'd have. He's probably also a lot weaker now than he was as the Destructor, but he's still big, strong and benign enough to make him a useful last-ditch option against other ghosts.
This is how the individual Ghostbusters made money in the five-year interim between the two movies.This only works by disregarding "Take Two" from the overall canon, but hear me out: The restraining order forbade the 'Busters from making money while ghostbusting. Nothing said they couldn't become rich beyond their wildest dreams by selling their story; The Real Ghostbusters is the result. It would probably look more like The Original Real Ghostbusters, with matching flightsuits and a Peter that looks a little more like Bill Murray at Peter's own insistence; also, Mr. Stay-Puft would be the unofficial mascot, not Slimer. Somewhere around Series 3, the Marshmallow Man starts to take a bigger role, and the show is eventually retooled to focus entirely on him. At this point, we see Movie!Ghostbusters in decline, with Ray and Winston doing kids' parties in a decrepit ECTO-1.
The camera-man has a fascination with Egon.This is something I noticed while I was marathoning the episodes: Whenever the camera needs to zoom in and do a close-up for dramatic effect on any ghostbuster - any ghostbuster at all - the choice is almost constantly Egon. The camera seems mesmerized with his blue eyes in particular. Now, this could mean a number of things.