Continuity mistake: When the slime is covering the museum an aerial view shows its surroundings empty. At the end of the movie, thousands of people gather around the place, yet the aerial view when the (superimposed) slime explodes is the earlier one, making it look as if the crowd had vanished, only to reappear a second later in close-ups. (01:37:50)
Continuity mistake: When the movie ends, Ray and Egon walk down the museum steps hugging each other. When the angle changes they are way apart from each other. (01:39:45)
Continuity mistake: There's a scene where Spengler talking to Ray about Iran running Vigo The Carpathian through the Occult Reference Net. We first see the computer screen from the side, with Spengler and Ray looking at it, and in the next screen we see the screen head on. The layout of text on the screen, the books piled to the right and the shadow on the wall to the left are all different between scenes. The close-up of the screen is obviously a different set-up, close but not right.
Continuity mistake: When Janusz is knocked out on the floor, his position keeps changing all the time depending on the angle.
Other mistake: In the Italian dub, Egon mentions that he raised the room temperature to 42°, which would be almost 108 F, instead of the correct 95.
Other mistake: In the Italian dub, the kids at the birthday party vociferously ask for their hero; Tree Man instead of the original He-Man. He-Man was very popular in Italy too at the time, it was not an obscure reference that needed any adaptation - not that there is or was any character named Tree or Tri Man in Italian pop culture.
Revealing mistake: When the [superimposed] pink slime and the bending tub try to attack Dana and Oscar, watch the tiles on the wall in front and you'll notice that they're not being reflected, just an empty space.
Other mistake: There's an unnatural jump-cut near the end of the movie, just before they shoot Vigo with the proton pack.
Other mistake: Dana leaves her home in such a hurry that she does not even put anything on her baby in the middle of December. She shows up at Peter's home, he phones Ray who then rushes out of the door saying he's gonna check Dana's apartment. Peter tells Dana that Ray is going to check her apartment, but their phone convo ended way before Ray had taken that decision, and he has no contact with the others till morning when they meet at the museum.
Suggested correction: Dana easily could have grabbed something that was laying on a table or piece of furniture that was on her way as she was running out of her apartment to dress Oscar in, or a good Samaritan could have given something as she made her way to Venkman's place. And Ray tells Venkman on the phone that he is going to check Dana's apartment.
Continuity mistake: After they trap the Scoleri Brothers, Spengler lifts his foot from the trap mechanism. In the immediate angle his foot is still on it, and he is lifting it again.
Revealing mistake: In the aerial angle of the Statue of Liberty walking down the streets, watch behind it: it is very evident where the matte painting was inserted: The street colour differs and the objects have way less definition.
Continuity mistake: When Dana is watching the couple arguing she has her arms crossed. A frame later, from a different angle, they are not.
