Character mistake: Given Billy still remembered and recognized him it seems strange Kate doesn't when she mistakes Daffy for Gizmo.
Suggested correction: Billy spent significantly more time bonding with Gizmo in the first movie - days and days. By contrast Kate had very little actual time with him.
Character mistake: In the beginning scene, the doctor cuts his finger open while performing the operation. However, despite the high risk for infection, especially given the extraordinary circumstances of the procedure, and despite the fact he's a medical professional... he doesn't immediately run to rinse off his wound and change gloves. And you can't argue it's Tomie's supernatural influence, because they haven't even seen her yet.
Character mistake: When Annie is in the red truck, she says that she'll be cooking for ten staff. When Alice goes to the beach, she tells Bill that everyone has arrived except for Annie. Even if she had arrived, there would only be eight of them: Christie, Annie, Ned, Brenda, Jack, Marcy, Bill, and Alice. Two shy of what she told the truck driver.
Character mistake: Roy says, "He thinks the wounds look self inflicted." But the doctor who said that was a female.
Character mistake: When Leon goes to see Susan Hoff with his photography portfolio she tells him he needs improvement. After she leaves, Leon tells Jurgis that he thinks she hated his work and Jurgis tells Leon "when she hates somebody's work she gives them about a minute, you got three." In reality, she actually did give him one minute almost to the second. (00:06:58)
Character mistake: Doreen/Mom told Rose she'd be back from the store "in a jiffy." Rose asked, "How long is a 'jiffy'?" and Doreen replied "in about an hour." "Jiffy" typically means VERY fast (perhaps as short as a nanosecond) and, even if people have different perceptions of how much time a "jiffy" is, an hour is excessive by general standards and does not reflect its true meaning. (00:32:50)
Character mistake: When Modoc is suggesting what type of blood to drink, he suggests pigs blood B-. Swine don't have B blood. They have A and O blood only.
Character mistake: When recruiting Burt to help repel the Graboid attack in the arctic, one of the team members says he's ideal for the job because of his experience hunting them on two continents, a reference to the first two films (Nevada and Mexico in North America) and Tremors 5 (Africa). However, this repeats the mistake in Tremors 5 in overlooking the Argentina incursion stopped by Burt at the beginning of Tremors 3, which gives him experience fighting Graboids/Shriekers/Ass-Blasters on three continents, not two. Burt, himself having overlooked Argentina in Tremors 5, does not correct her. And it's not as if the film is completely ignoring Tremors 3, since it shows the flashback of Burt being swallowed by a Graboid in that movie, which is how he got infected with the deadly parasite killing him here.
Character mistake: In the very first scene, in the first shot you see a sign in Spanish that says "NO PASE por orden del departamento de arquiologia". The correct Spanish word is arqueologia.
Character mistake: During the surgery, one of the surgeons says to give the patient 25 cc's of cyatril. Then one says make it 35 cc's. 35 cc's (or 35 mL) is a full large syringe. The other doctor uses what looks like a 3 mL syringe and it's only partly filled. It seems the surgeons wanted 0.35 cc's.
Character mistake: Jill states that a 5 kiloton nuclear weapon will sanitise the city, however, such a yield is far too small to destroy the city. (00:42:00)
Character mistake: When the sheriff confronts Charlotte after she has shot at the bulldozer operator, he tells her that her gun is unlicensed, but he will overlook it. Louisiana does not have, and never has had, any form of gun licensing or registration.
Character mistake: Zoe states that Lilly's condition is very contagious and will spread through the camp if they don't go out and get the proper medical supplies they need. She puts Lilly in quarantine... and then proceeds to visit Lilly with no protective equipment. No mask, and even touches Lilly with her bare hands before going back out to the rest of the people. (00:19:20)
Character mistake: Given how smart the lead is he doesn't seem to know the proper dosage of sleeping meds he put into his mother's coffee. He placed in enough to possibly cause an overdose.
Character mistake: Daphne's mother is the one who pressed her husband to tell her the truth, but she is cheering when he says about the basketball anecdote that it was 'real', when later he corrects himself saying "real-ly me, disguised as a mascot." (00:17:25)
Character mistake: Leland Palmer handles Laura's body without any gloves when wrapping her and disposing of the body. As with any respectable FBI investigation, upon finding her body and checking for fingerprints, they should've connected Leland to Laura's death within days. (02:05:00)
Character mistake: When Ethan Thomas objects to Dr. Adanie's testimony, he does so on the grounds of "silliness." Silliness does not fall under the federal rules of evidence, and any lawyer worth their salt would know this.
Suggested correction: During the Manson trial in real life, the prosecutor objected to a completely pointless question the defense asked a witness on the grounds of being ridiculous. The judge agreed and sustained the question. In his book Helter Skelter, Bugliosi even acknowledges there's no such rule, but the judge sided with him. The prosecutor in this film is grasping at straws, since nothing that would fall under the rules of evidence would apply to his objecting to her scientific testimony.
Not true, he can object on the grounds of relevance. The YouTube channel Legal Eagle, which is run by an actual lawyer, even stated so. The same logic applies to the Manson trial. If a lawyer feels that a question is ridiculous, they can object on the grounds of relevance.
In a case involving demonic possession as a central aspect of the defense, there's no way relevance could be grounds to object to her testimony. Her testimony dealt with possession from a scientific point of view, but he objected because it was for the defense. The judge in the film even allowed her testimony stating that they'd heard a lot of scientific evidence supporting the prosecution's case and it was fair to hear from an 'exorcism expert'.
As for the Manson case, try reading the book written by the prosecutor. It even states in the transcripts that he objected on the grounds of a question being ridiculous (even if, in the end, it would actually be relevance).
Just because a lawyer in real life was able to successfully object on the grounds of ridiculousness doesn't mean it would suddenly become a good practice. That would be like saying basketball players should just wantonly heave half court shots, because sometimes they go in. The premise of your suggested correction was also that the lawyer had no legal grounds to object on, and that is objectively false. As I mentioned, the lawyer behind the LegalEagle YouTube channel even said otherwise.
Character mistake: John shot at the "werewolf" but wasn't successful in hitting it. Instead of pursuing the werewolf, who he supposedly was determined to catch, he let it run away. Alcoholic or not, a sheriff's deputy should have done everything possible to try to capture the creature that was terrorizing the small town. By not even attempting to follow the werewolf, John missed the one opportunity he - or anyone else - had thus far to potentially put an end to the senseless and tragic murders of young ladies. (00:55:35)
Suggested correction: Dude's daughter was attacked and bleeding from the head, of course he didn't pursue it.
Suggested correction: He didn't go after the wolf because his daughter was hurt, and his (albeit misguided) parental instincts took over. It's not at all a character mistake for him to prioritize making sure his daughter is all right over chasing a perp. Most parents would probably do the same thing.
Character mistake: A detective (Briggs?) told Sonny, " that I was stupid enough to believe your dark fantasy NINE-ELEVEN call." [emphasis added] An American law enforcement officer, in particular, should know and use "nine-one-one" (911) when referring to the nationwide emergency telephone number. "Nine-eleven" (written 9/11 and NOT 911) is used to refer to the September eleventh (9/11/01) terrorist attacks in the U.S. (01:15:57)
Character mistake: Andy speaks of Billy changing in the two months after he was hired when he was hired in the spring months ago.