Continuity mistake: When the man drives his car into the cornfield and hits the boy with his vehicle and rescues the mom and her son they run out of the cornfield and back to the house. After the house catches on fire they run outside and his car is parked in the driveway.
Continuity mistake: After Claudia leaves the ride without her cell phone it cuts to Fin driving his car into dense fog, and in the exterior shots the Toyota's front grille emblem as well as the license plate inexplicably vanish, and then reappear.
Factual error: The 'Post Office' is nothing like an English one would have been, even in a remote rural location in Victorian times. It seems to have been transposed from the American Wild West.
Revealing mistake: When Krampus walks toward Max after he yells at him to give him his family back, wires are controlling Krampus' arm. (01:24:30)
Deliberate mistake: When Quinn is texting the boy next door, he responds too quickly for it to be real. She sends the "So you think I can stop traffic, huh?" text and gets a response within literally two seconds. She then sends the "Did I wake you up?" text and gets two responses within five seconds. Texts usually take several seconds (at least) to be delivered and opened, so even with great service and lightning-fast fingers, this is obviously far too quick.
Continuity mistake: When Gordo leaves Simon and Robyn for a few minutes to handle a work thing, Simon starts mocking Gordo in his absence. Simon tells Robyn that Gordo wants to nail her and Robyn says "Stop it," but Simon continues his mocking of Gordo. At the end when Simon is listening to the recording that Gordo made of that conversation, Robyn's "Stop it" is absent.
Continuity mistake: Spoiler alert: About halfway through the movie, we see Emma Roberts coming out of the shower, and the camera focuses on the gunshot wound on her shoulder, with the round scar of the entry wound on her back, and the much rougher, ragged scar of the exit wound on her front. Then at the end of the movie, where it's revealed that Kiernan Shipka and Emma Roberts were actually playing the same character, just nine years apart, Kiernan Shipka gets shot by the police officer when he finds her in the room with the severed heads. Problem is: she was facing the officer. The scars on Emma Roberts are the wrong way around. (00:31:05 - 01:15:35)
Continuity mistake: Ray is on the phone with his girlfriend; as he says "Whatever you say, Ashley", the green scrapbook is closed. It is open again next, just as it was open before. (00:02:00)
Visible crew/equipment: When Matthew is following Nina's cries for help through the woods you can see numerous set lights in between the trees (in the distance). (01:09:43)
Continuity mistake: When Griffin gets out of bed, when he hears the clown song he pushes the bed sheets forward about 3 feet from the pillow but when his dad goes into Griffin's room, the sheets have been pulled up about half that length.
Continuity mistake: When the party goers are escaping, Ben begins tying the door closed, but in the next shot, there are still people running up the stairs escaping. (01:19:30)
Factual error: In the end credits, when the listing of songs used in the film is rolling, the Kiss song is listed as "Detroit City Rock." Actually, the song title is "Detroit Rock City." (01:38:10)
Continuity mistake: The blood on the good guy's white shirt continuously changes through the last chase. (01:22:00 - 01:26:00)
Continuity mistake: Mike and his wife are talking in the street. She is crying and tells him that "It's never him." Twice, with a reverse shot and a line of dialogue in the middle, a woman with a light green jacket gets on the sidewalk behind Nicholas Cage. (00:40:05)
Continuity mistake: The belt around the dude's head changes position as he's tied down on the table. (00:39:45 - 00:40:45)
Continuity mistake: When the big truck chases the red car and repeatedly rams into it you can hear broken glass, etc. but in the next shots the back of the car is intact, red and shiny, without a scratch on it. (01:05:00 - 01:06:00)
Factual error: The producers took a lot of pride in using period-accurate furniture and clothing. But the family's house and furniture aren't remotely accurate for their actual situation. The table, the chairs, the house with a sleeping loft - all those took technology and manpower that they didn't have, and we've already seen that they had nothing to trade either. And they have more furniture than could have fit in that wagon.
Factual error: Tina's striptease dance is mentioned several times as a notable scene in the fictional 1986 movie 'Camp Bloodbath'. When that scene plays out, the song Tina dances to is Warrant's 'Cherry Pie', which wasn't released until 1990.
Character mistake: In his opening prologue, Burt says the Graboids have been contained to the Northern Hemisphere, showing a map highlighting the Graboid attacks of the first film in Nevada and the second film in Mexico. However, it overlooks the Graboid/Shrieker attack in Argentina, in the Southern hemisphere, shown at the beginning of Tremors 3, an incursion Burt personally put down. It's not like it was classified - characters in that movie talk about it being reported by CNN, and characters in the Tremors TV series talk about it as well. And it's not like Tremors 3 is no longer canon, since Burt makes two references to being swallowed by the Graboid in that movie (which also becomes a plot point in Tremors 6).