Revealing mistake: During the opening theme, when the children are watching the magician, you can tell they were not actually filmed together. The magician scenes are filmed more professionally using a sharper tape or film image, whereas the children scenes look more like a standard fuzzier film-type such as on a projector (primarily used at that time).
Other mistake: You don't have to look further than the name; the title of the series is "Knight's and Magic" instead of "Knights and Magic".
Plot hole: Loki states while on trial that The Avengers should be on trial for traveling through time to change the timeline. How did he know they came back through time?
Suggested correction: He recognized that there were two Tony Starks in the lobby by the smell of their colognes, and combined with all the other unusual shenanigans going on, he correctly deduced the Avengers travelled through time, though he incorrectly thought it was to prevent his ascendancy.
How exactly do you distinguish the smell of cologne as belonging to two separate people? But besides that, it's pretty wild to jump to a conclusion about time travel when it could be that someone else happens to be wearing Axe.
I'm sure he simply recognized his voice.
Factual error: Many elements of Marlott's trial and execution are incorrect. The judge sits with two assessors (a European practice, not a British one). He is addressed as 'Your Honour' instead of the correct 'My Lord'. He instructs the jury to find Marlott guilty and then goes straight to sentencing, which would never happen; a judge can instruct a jury to acquit, but not convict. He puts the black cap on himself, instead of an attendant doing it. The form of words for the death sentence is incorrect. The chaplain (who appears to be Catholic, not Anglican) gives a speech at the scaffold.
Continuity mistake: When Marshall first finds Trip's letter, he holds it from the left side. In the close-up, he's holding it from the right side. (00:02:10)
Firefly, Light My Fire - S1-E1
Revealing mistake: Courage winces and reacts before the stereo-zapper is fired.
Other mistake: When Teela is at Snake Mountain, she overhears TrapJaw saying how Skeletor's electrical creature will control all of the machines at the palace. When Teela returns to He-Man, she says that the creature Skeletor created is called Byte. There's no way for Teela to know the name of the creature, since TrapJaw never referred to it by name. (00:14:24 - 00:15:20)
Gortimer vs. The Mobile of Misfortune - S1-E3
Visible crew/equipment: When Stanley is riding the kart in the race, the shadow of the camera equipment is briefly visible bottom right, just before the kart starts to fall apart.
Plot hole: The powerful 'amulet of protection' makes the bullets strike the shooters instead of John. Clearly it works not just against magic and other ethereal threats, but also against physical attacks. So why does he almost get knocked over by a car? True, he isn't seriously injured, but he was thrown to the ground. The amulet should have pulverised that car or bounced it at least two blocks away.
Factual error: Helmuth von Moltke is addressed and referred to several times as Field Marshal. He wasn't promoted to that rank until 1871. He was a lieutenant-general during the Second Schleswig War in 1864.
Continuity mistake: The professor knocks a hole in the side of a tunnel and hot water and steam gush out. The group is then distracted by a boulder traveling through the tunnel. After the boulder passes, there is no longer any steam or water gushing from the hole in the wall.
Continuity mistake: Multiple times throughout the show, Kimber can be seen in quick shots with light pink hair (the same color as Jem's), when her hair color is actually a dark pink/red color. (02:00:00)
Continuity mistake: When Eden confronts Kinsey by the lockers, as the angle changes so does Kinsey's arm. In some shots, she has her arms crossed and the locker door is closed, in some shots she has one arm up, holding the (open) locker door.
Other mistake: In the end credits, Juliet Waley is credited as "Juliet Way."
Character mistake: Ryan tells Jack that Darius turned into a werewolf right in front of his and Micki's eyes. Ryan and Micki never witnessed Darius' transformation into a werewolf at all.
Factual error: Thomas holds the Gendarmerie rank of Capitaine (by which he is frequently addressed by his subordinates), and thus should wear three horizontal silver bars on his epaulettes. However, in the only scene where his rank is displayed he instead wears the two chevrons of an ordinary gendarme.
Flash Gordon and the Planet of Death - S1-E1
Revealing mistake: In the flashback of the scientists' fate on the planet of Death, the sole survivor manages to run away and avoid the ray of "Belfagore" (which is just a big flashlight). Problem is, he does not; before hitting Bending behind him, the beam fully lit up his back, but he suffers no adverse consequences, no dropping dead for Jefvus. (00:06:40)
Continuity mistake: After he has destroyed the television Mr Gore tries to light his pipe. If you look outside you can see several cars parked outside the Gore's house, in the following scenes outside this house all the cars have gone. They couldn't have been driven after "the changes" had started.
Other mistake: Two Tiffs can be seen for a few seconds when King Dedede and Escargoon drive in.