Continuity mistake: When Pierce's wife is walking in her auto shop they pan down to show her red Louboutin heels, then they cut to her walking in her office, and when they show her shoes again they have a tan sole.
Visible crew/equipment: After going through the turnstile in Oslo, the Protagonist walks up to an ambulance, knocks out the driver and steals it. When he begins to drive off, the shadow of a huge stage light can be seen cast on the side of the ambulance. (01:44:34)
Continuity mistake: Angelica has flowers on her dress. During the wedding, they disappear and reappear between shots.
Continuity mistake: When driving the silver Audi A6 the first time, the version they are driving is a diesel, seen by the exhaust pipes facing down towards the ground with a bend. In the next shot they are driving the petrol version of the same A6, seen by the exhaust pipes holes facing directly out from the car. (01:18:33)
Continuity mistake: During the whack-a-robot game, a big chunk of the broken robot lies on the counter, but it disappears a shot later.
Continuity mistake: Chen Honghui extends his hand to "the little man" to help 'him' back on his feet, but Mulan pulls her sword on him. The sword strap dangles freely in the shots by the side, but it is held up in the close-ups of the blade pointed at his neck. (00:29:45)
Continuity mistake: During the final fight at the very end of the film, pay attention to Millie's bloody nose. At first, there's an equal amount on either side. But a few seconds later, the suddenly less blood on the left side of her face and more blood on the right side.
Factual error: The aircraft shown in the movie is a DC-3, however the correct aircraft would have been a Convair CV-240 which is a very different model.
Continuity mistake: When the boy is about to eat his corn bread, the knife on the left keeps changing positions between shots.
Continuity mistake: The protagonist receives her gift from Molly Shannon. She unwraps it and puts the discarded wrapping on the counter. When we see it again at the end of the scene, the wrapping is much less torn apart than the first time around (or at least has been arranged neatly). (00:09:45)
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: In the Spanish release, the name of the family store is written in Spanish, but inside the place it's in English everywhere. This is a very common mistake in foreign kids' films released in Spain.