Other mistake: How could Egon get down to the ground floor so quickly? I mean, a few moments earlier, he poked a guest in the shoulder. And, why would he go back down to the first floor in the first place? They said that nothing happened on any floor except the twelfth.
Continuity mistake: At about the middle of the film, when the Ghostbusters are rising to fame and are appearing on the front of newspapers and magazines, the photograph on the front of the New York Post is taken from the end of the film, just before the four of them cross the streams from their proton packs. (00:39:37)
Continuity mistake: When the eggs pop out of her bag and start cooking on the counter, they're in different positions depending on whether it's a close up or wide shot. (00:18:55)
Revealing mistake: Towards the end, when the ground is shaking and breaking up, a police car falls halfway into a hole in the road. When the smoke clears a little you can clearly see two white poles, one on either side of the back left wheel, holding the car in place. (01:21:04)
Revealing mistake: In the ballroom scene, when Slimer is flying around the chandelier, he disappears for a few frames when he reaches the far side. [This animation is mentioned in the DVD commentary. The film makers were generally unhappy with the entire animation and the fact that the representation of the apparition did not resemble those previous and that the movement was very unconvincing.] (00:35:05)
Continuity mistake: When Winston gets hired, Venkman and Stantz have just come back from a job. They're covered in slime and Venkman's smoking. Ray gives Winston an armful of traps. We then cut to Venkman chatting to Dana after a rehearsal, so we assume it's later, maybe even a different day. After that scene though, we then cut back to Stantz showing Winston (wearing the same shirt) what to do with the traps, and Venkman talking to the guy from the EPA. Venkman's got the same slime pattern on his shoulder, and is still smoking. Looks like the Dana/Venkman scene was in the wrong place. (00:42:00)
Revealing mistake: When the police car falls into the hole, if you watch the ground that's rising up in front of it, when it finally comes to a stop, you can see how light it is because it bounces, and you can tell that the pieces of the pavement are moved by hydraulics. (01:20:45)
Revealing mistake: Near the end of the film when the Ghostbusters take cover in a small corner and come up with the "cross the streams" plan, look closely at Peter's proton pack, you can see that it is a foam "stunt" pack as there is a small sticking out part that keeps squashing against the wall behind him. (01:32:25)