Continuity mistake: Trevor is driving the Ecto-1 and complains that Podcast is breathing on him. We see Podcast very close to him. The shot cuts and Podcast is now further away.
Continuity mistake: Phoebe and her mother are by the door of the farmhouse, waiting for the pursuing demons to appear. The shoulder strap of Callie's dress is lowered in most shots, but goes back up suddenly (and only) in an intermediate shot.
Factual error: Trevor was driving ECTO-1 at over 60 mph. Podcast was driving the remote car and it was pulling away from ECTO-1. There is no way that the remote car could be going faster than ECTO-1, unless it was souped up, which it didn't appear to be when looking at it.
Suggested correction: There are plenty of RC cars on the market right now that anyone could buy that are capable of going 60+ MPH (the fastest can hit about 100 MPH). And if you take them apart, they don't look "souped up" at all. They just look like regular RC cars inside. Components don't have to look fancy to function fancily. You also have to account for the fact that the movie is highly fantastical, so there's no telling what kind of technology the RC car uses... for all we know, it could be nuclear-powered like the proton packs.
Other mistake: When Trevor attempts to start Ecto-1's engine the camera shows a very incorrect engine. A Triumph Herald/Spitfire 4 cylinder that is less than 1 to 1.5 litre.
Character mistake: There are signs out front as the Spenglers arrive at the dirt farm. One of the signs is a call back to a scene in Ghostbusters 1984. In the scene, Ray quotes the book of Revelation: "And I looked, and he opened the sixth seal, and lo, there was a great earthquake. And the sun turned black as sack cloth, and the moon turned blood." When Finn Wolfhard reads it he misquotes the line saying "The sun became as black as cloth."
Deliberate mistake: The mother jumped through the window, shattering the glass, but did not get cut or tear her clothes. (01:28:55 - 01:31:10)
Continuity mistake: When Gary is freed from his ghostly form he says "Oh, that was weird" and a shot later his left hand is suddenly next to his face.
Continuity mistake: After testing the proton pack, Phoebe raises her hand to adjust her glasses. A shot later her hand is lowered.
Other mistake: Egon's old jumpsuits fit the kids perfectly, but he was a grown man and these are young children.
