Genesis (2) - September 13, 1956 - S1-E2
Deliberate mistake: When Sam ejects and lands on the ground, the closeup is a flipped shot, note the "US Air Force" is backwards on Sam's helmet. (00:19:10)
Deliberate mistake: The police force in the town is the Gendarmerie, the standard issued firearm is the Sig Sauer P2022 in 9mm. The police officers on this show carry a Beretta and not the 9x19mm one which is the model 92fs, they carry a never issued Beretta 84 chambered in .32 acp or 9mm short. Plus they use some weird holster where the gun arches out and hangs low like a cowboy holster and dangles around. Easy for a suspect to gain control of the officers gun and this happened in this episode.
Deliberate mistake: As Chief Vickery, in present time, patrols Wind Gap in his car he passes by the barbershop. From his POV, through the car window, we see four men sitting outside. The same men were also seen in Episode 01, but from young Camille's POV as she and her sister pass by the barbershop in 1992. The show hid a load of easter eggs and signs throughout all episodes. They would hardly make such a mistake. More likely, the repeat was to underline Vickery's backward, stepfordian attitude.
An Affair to Dismember - S1-E8
Deliberate mistake: Right after the credits, we see an establishing shot of the mayor's house but it's a reused shot from episode four from when Jake and Lexy snuck inside, just without the digitally added smoke. What gives it away? The fact you can see Jake and Lexy at the bottom corner sneaking in, wearing the clothes they wore in episode four, even though they're already inside and wearing different clothes.
Deliberate mistake: To fix the error of the Enterprise firing phasers from the torpedo bay, the Blu-ray version uses footage from "The Best of Both Worlds" to show phasers firing from the dorsal emitter. In doing so, they created a new goof; the planet El Adrel is not visible in the background during these shots.
Suggested correction: I rewatched the original version on the old DVDs. El Adrel wasn't visible in the original either, so this is not a new error.
Deliberate mistake: When the family is trying to get money from Al at the start of the episode, he throws it on the ground making the rest of the family to dive on it and you can see Bud get it, then throw the bunch of money in the middle of Kelly, Peg and Bud so they can all get to it instead of taking it all. (00:02:10)
Deliberate mistake: David is shown to have an illegal weapon in his home even though gun control is quite strict in the U.K. Sadly, this is quite a common practice by returning war veterans who feel safer with a gun in the house, as they often suffer from PTSD, as David does.
Deliberate mistake: After Bud overhears the plans for Flipper, he decides to hide his dolphin. When he boards the skiff, there are two flipped wide shots before they head out. Note the reversed dock, launch, and "Whaler" on the skiff.
Mojovision - S2-E11
Deliberate mistake: Some of the footage of the X-Men in action that Major Domo shows Mojo is clips from previous episodes, and even clips from the show's opening theme. (00:03:36 - 00:04:22)
Deliberate mistake: The last season touched on Infinity War happening - this season jumps forwards a year, meaning that we should be one year into the "blip" (or snap), with half the universe missing. But The Team is all together, and the world/universe is utterly unaffected. Largely a byproduct of disagreement between the film and TV sides of Marvel, plus scheduling vagueness meaning they couldn't risk spoiling Endgame if they came back on the air before that was released. But considering the show is 100% part of the MCU, that's a pretty massive contradiction.
Deliberate mistake: When the sewer worker is trying to escape the Lizard, the fast lanes in both directions of traffic are visibly clear for several blocks, which is extremely unlikely in downtown New York. (00:01:10)
Plane Death - S1-E14
Deliberate mistake: When the bad guy goes to smash a table onto Michael Landon notice the plate of glass in front of him, visible. The glass is there so Landon doesn't get hurt and to make the table break into pieces in front of him.
Thank You and Good Night - S1-E8
Deliberate mistake: In the Maisels' 1954 wedding reception flashback, Midge hired professional dancers who perform the "Bottle Dance" (where they slide on their knees). This famous dance, often performed at Jewish weddings and social events, was choreographed by Jerome Robbins for "Fiddler on the Roof," which debuted on Broadway in 1964. It did not exist in 1954 but, as an inside joke, while Midge watches, she says, "That's really good. They should do something with that."
Deliberate mistake: In the restaurant after their daughter finishes talking to Niko, Erik turns the tablet device around and sets it on the table to talk to Niko. From his perspective, he is looking down at the screen. But in the other shots from Niko's perspective, where he is a life sized hologram, his figure is shown looking up and meeting her eyes. But from her perspective it should look like he's looking down at the table.
Deliberate mistake: Amanda survives a plane crash into the ocean, hurricane winds in a life raft, then experimentation and attacks by giant microbes inside the alien probe. Yet when she and the others are rescued at the end, not one strand of hair is loose in her 1960s "beehive" hairdo. (00:49:05)
Deliberate mistake: When Fluttershy is telling off the cockatrice, her back legs and her wings turn to stone. But when she gives it the stare and the camera is right in her face her wings are outstretched.
Episode XCII - S5-E1
Deliberate mistake: Jack stops his motorbike beside a stream, and Jack's weapon strap crosses over his left shoulder when he walks over to have a drink. The problem is when we see Jack's reflection in the water, his image is not reversed; note the strap is still crossing over Jack's left shoulder. (00:07:20)
Deliberate mistake: When the young kid breaks out of Jeff's apartment, the ladies freak out that he's naked, when he's wearing black underwear. And then shortly after they shriek to police that he was buck naked when he wasn't.
Snow Place to Go/Dunce Upon a Time/Gems the Breaks - S2-E4
Deliberate mistake: Dunce Upon a Time: When Lumpy falls off the beanstalk and hits the ground, his left antler is missing. Probably done deliberately so that his head could fall flat on the ground. (00:14:03)
Better than Average Cory - S6-E5
Deliberate mistake: When Rachel is choking and writes down "I'm choking to death" on the paper on the counter so Jack will help her, you can see she is just scribbling the pen across the paper and not actually writing anything. (00:06:36)