Actor Allusion: Vigo's full name was later revealed to be Vigo Von Homburg Deutschendorf. When Vigo steps out of the painting, he is played by German wrestler Wilhelm von Homburg and baby Oscar was played by twins William T. and Hank J. Deutschendorf.
In the comic series, Ray is visited by the ghost of Joliet Jake.
The Danza: Two throwaway examples in the first ten minutes: Alice Drummond has an opening-scene cameo as Alice the frightened librarian, and Jennifer Runyon as Jennifer, the test subject for whom Peter compromises the scientific method.
Almost in this case: Ilyssa Selwyn is voiced by Alyssa Milano.
Deleted Scene: One such scene in the second movie helped explain the moment when Vigo possesses Ray during the final showdown. During the first museum visit, the guys examine the painting of Vigo and fans may remember Ray being hypnotized and needing to be snapped back to reality. This was supposed to lead into a sequence where Vigo tries to use Ray to crash Ecto-1 and kill the Ghostbusters in a traffic accident. Winston manages to grab the wheel and save the day, while Ray - no longer under Vigo's influence - can't account for what just happened. Note that a couple of clips from this sequence were used in the montage - specifically Ecto-1 crossing through an intersection and Peter in the car, looking bewildered.
From the first film, during the Good Times Montage, Ray is shown dreaming about a female ghost hovering over him and unbuttoning his pants for some spectral loving. This was actually part of a larger scene later in the film where he and Winston were investigating an army fort, and this was where they were coming back from before the "dead rising from the grave" scene.
A number of scenes from the first film were either originally longer (such as the confrontation with the Dean when Peter, Ray and Egon are fired, Peter arguing with Dana in her apartment after he checks out her fridge, Peter and Ray talking with the Mayor before going off to face Gozer followed by Peter interrupting a moment between Egon and Janine) or completely cut (the Stay Puft Marshmellow Man's hat falling on the crowd at the end).
The Dev Team Thinks of Everything: Ivan Reitman shot alternate scenes removing much of the profanity for television broadcast, with dialogue just as good as the original.
A series of alternative takes for the Ghostbusters' little commercial recently came out on the internet; many of these contain alternative names for their business in case a deal with Filmation (the studio which created the live-action series The Ghost Busters) couldn't be brokered. Such names include "Ghoststoppers" and "Ghostblasters" (ironically enough, there's an interactive dark ride called "Ghost Blasters").
Executive Meddling: According to Ernie Hudson, this is the reason why the sequel isn't seen as the same level of quality as the first. After executives saw how popular the first movie was with kids, they forced some changes onto the second movie to make it more appealing to a younger audience. Much like what happened to later seasons of the cartoon, they tried to fix something that wasn't broken; thankfully, the movie didn't suffer too much from it.
Also the reason Winston is a lesser character — when Hudson signed on, Winston was in the script from page eight (rather than toward the end of act 1), and was by far the most technically competent and qualified of the Ghostbusters. Aykroyd apparently still blames himself for Hudson's character being sidelined.
The very bouncy blonde woman who briefly dances with Louis Tully is Jean Kasem, wife of voice actor & radio personality Casey Kasem. In fact, Jean's very brief role in the film is one of her best known roles!
Max von Sydow is the voice of Vigo in the second film as well as the game.
Alyssa Milano is Dr. Ilyssa Selwyn in the game.
Peter MacNicol, who portrayed Janosz in II is also the voice of the Mad Hatter.
Paddi Edwards, the voice actress who gave Gozer its voice, also gave her voice to a familiar pair of electric eels.
I Am Not Spock: According to the DVD commentary, the first movie ruined William Atherton's life, what with random people yelling "Hey, dickless!" at him on the streets.
Off-the-Shelf FX: Venkman's ghost-sniffer, also known as the "Bacharach Chemical Sniffer," which is used primarily for detecting gas leaks. This also carries over into the guys' Homemade Inventions (a kitchen colander with wires and things on it, for one).
One of Us: Ray in the cartoon. He's very into cartoons and superhero comic books.
Throw It In: There are varying accounts of how much of the final films were improvised, from a few select lines to a good majority of the films.
A definite example is the majority of Louis' party in the first film, which was not only one continuous take, but almost entirely improvised.
In the Ghostbusters' commercial, Egon looking down to find his mark was an actual flub by Harold Ramis that everyone agreed fit the character.
What Could Have Been: For a great movie, Ghostbusters varies tremendously from its original concept. Aykroyd's original script called for multiple groups of ghostbusters who traveled through time and fought ghosts in different dimensions. This idea was rejected as technically unfeasible in 1985. Supposedly, the special effects would have cost over $300 million. Ivan Reitman re-purposed the script as a "going into business" story to make it more accessible to audiences.
Many actors were switched out or not intended as their original performers, the part of Ray Stanz being by far the most stable as it was designed for co-writer Dan Aykroyd almost from the start.
The part of Venkman was written for John Belushi, but he died before that could become a reality. The part was then offered to fellow Saturday Night Live alum Chevy Chase, but he declined. Bill Murray, the driving force of the movie, was a last-minute addition to the cast. While Murray made the role his own, several lines are clearly intended for Belushi, such as the speech after the university fires them. It sounds corny from Murray, who usually plays a cynic, but Belushi was good with such bombastic speeches.
Eddie Murphy was to play Winston, who would have been part of the original group along with Ray, Peter and Egon. He was described as a former Marine and Ph.D.-level scientist, the original script called for Winston, not Venkman, to be slimed in the Sedgewick Hotel. Murphy was left out because they didn't want the movie to be perceived as an Saturday Night Live-inspired film (even though Harold Ramis was never an SNL cast member; he was on SCTV, which some people see as a Lighter and Softer Canadian version of SNL), and because he was busy with Beverly Hills Cop at the time. Winston was then re-written as more of a blue-collar everyman and eventually given to Ernie Hudson, though Word of God has it that Winston was a Marine and a Vietnam veteran before joining the Ghostbusters (this never comes up in the films or the animated series, the latter of which has two episodes stating that Winston was previously a construction worker).
The part of Louis Tully was initially offered to John Candy, who wanted to play him as an odd German guy who owned dogs. The directors didn't like this idea, since there was already so much dog imagery in the movie, but couldn't bring themselves to replace him. Fortunately, Candy passed on the role, and they offered it to Rick Moranis, who had a much better take on the character. It helped, too, that Moranis, Candy, and Ramis were all friends since Second City together, and understood that the best guy for the role was the best guy for the role.
Harold Ramis was not originally intending to play Egon, he never had much success as an actor and was just interested in writing for the film. After a hard time casting for Egon, Aykroyd and Reitman suggested that Ramis would be perfect for the role and as soon as he read for it everyone agreed.
Michael Keaton was offered the choice of playing either Venkman or Egon Spengler and declined both.
The Stay-Puft Marshmallow Man was on the chopping block. The producers were worried that audiences wouldn't buy the character, and were prepared to produce a different ending if test audiences didn't react positively. Fortunately, they did, even though the test version of the movie lacked completed special effects, making him more of an Ultimate Evil.
The second movie was apparently supposed to start getting into the "other dimension" aspect of the mythology but that was changed at the last minute to something closer in plot to the first movie. Bill Murray was upset with the radical changes to the script and it is another reason why the third movie has been in Development Hell. Unfortunately, it is this similarity to the first movie that contributes to its overall poor reception. The Game was able to finally get into this aspect of the premise, being cheaper to do than a movie format.
Originally Gozer was going to take the form of a man in a business suit and would have been played by Paul Reubens. Reitman was the one to devise the androgynous form at the last minute, believing it would work better as a supernatural manifestation rather than the rather mundane look. However, the Video Game's design of Ivo Shandor is said to be based upon what Paul Reubens might look like in ten or fifteen years' time.
According to Chevy Chase the script he read was much darker, scarier and more violent than the film that actually got made.
Aykroyd's original script was said to have been much more epic in scope, with the Ghostbusters as a kind of large scale police force with more members on call for people to contact when in danger, but he was told his idea was simply too expensive for what could be achieved on a 1980s budget so he scaled it back until it became the film we know and love today.
Harold Ramis' death in February 2014 may or may not have upset the production of Ghostbusters III. It's probably worth mentioning that even though Egon's appearance in the film was supposedly going to be very brief anyways, fan response to the continued work on the third film is almost entirely extremely negative, considering it insulting to Ramis' memory.
Word of God: Harold Ramis stated in the commentary that it was one of the first movies to use the word "slime" as a verb.