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: The commanding officer (Donnie Yen) intervenes to stop the sword-pointing nonsense with his kung-fu badassery. He easily disarms the two litigious rookies and holds both their swords, but the pose he strikes is a different one in the two shots; Mulan's family heirloom is held alternatively low and high. (00:29:55)
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.
Revealing mistake: When Millie jumps on her shop teacher's back, the teacher switches from the actor to a stunt double as they begin to tumble about. Noticeably, his hair suddenly gets much darker and has less gray in it. You can also get brief glimpses of his face, and it's obviously not the actor.