Deliberate mistake: Richie was an infant in season one, and beginning with this season, he has been aged up to at least 3 years old while none of the other characters have aged up.
Deliberate mistake: In the butter skating scene, the boys signing Paisley's cast are not writing anything. They are just pretending and their pens don't even touch her cast.
Jeannie, the Hip Hippie - S3-E6
Deliberate mistake: Phil Spector is credited as having played "Steve Davis", but that name is never used in the episode; he is instead addressed by his real name.
Log 1: The Impossible Mission - S1-E1
Deliberate mistake: Halfway through the episode, they are chasing car thieves in a drainage channel. The thief's car comes to the end of the road and crashes into a deeper gully. You can see that the windshield has been taken out of the car, although it was previously there. They cut away and when they come back, parts of the windshield are back in the car, but the whole center is missing.
Deliberate mistake: In this episode, it is revealed Donna and Robert got together because Robert saved her from a water fountain. In "Another Bad Thanksgiving", it was shown Donna's sister introduced Robert to Donna. (00:02:20)
Deliberate mistake: The ghosts often walk around furniture even though it was established that they can walk through solid objects.
Suggested correction: Just because they can walk through solid objects doesn't mean they have to. They were used to walking around things in life so just carry on doing so as a reflex action. They often use open doors too, only walking through walls when it's more convenient for them to do so or the doors are closed.
Deliberate mistake: They show footage of Max and Larabee scouting out the entrance to a bank. This same footage was used in the earlier episode "The Treasure of C.Errol Madre".
The Trouble With Mr. Bean - S1-E8
Deliberate mistake: When Bean is putting on his socks as he is driving, his foot presses the horn in the centre of the steering wheel. Except that the horn control is actually on the right-hand column stalk (you can see the horn symbol on it). This was most likely an added comical sound effect.
Deliberate mistake: Morgan turns on the stereo and starts dancing on the sofa with her doll. She then tosses her doll, which tips over a plant and breaks the glass on a set of French doors. The stereo magically stops the moment the glass breaks.
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.
Deliberate mistake: Although it was done for plot purposes, no school photographer would only take just one shot of a class photo. They generally take up to 15 to 20, as it is difficult to get everyone to look at the camera and smile at once (and hopefully not pull silly faces).
Deliberate mistake: After it is revealed Won-hyung has taken over Yeom's body, he is shown walking alone on the street and says aloud "She's not afraid of going to Hell? I can't make it so easy for her. Will she be able to leave behind the person she's been pining for so easily? I can't wait to watch the heart-rending sight." There is no reason for him to say this out loud. He is alone and not talking to anyone. The only reason he is saying this is so that the audience knows his plan. (00:33:23)
Deliberate mistake: When the show premiered on March 18th, 1981 Ralph's last name started out as Hinkley, but after a couple of episodes had aired on TV, on March 30th a man named Hinckley shot then U.S. President Reagan and three other people, so in the remaining episodes of season 1 Ralph's last name was changed to Hanley. His last name was changed back to Hinkley in season 2.
Deliberate mistake: Inside the home that has been infested with Evil, the state police confront a possessed girl who attacks them. After some futile gunfire, the possessed girl is still standing. The female officer goes for her backup gun, which for some reason is a small over-and-under Derringer (meaning she has two shots maximum). She ends up firing the Derringer five times in just a few seconds, with explosive damage and without reloading. Director Sam Raimi probably staged the 5 gunshots on purpose, knowing that a two-round Derringer was a ridiculously-limited piece of firepower. Raimi probably did this as a tongue-in-cheek tribute to Ash's bottomless double-barrelled shotgun from Evil Dead 2 and Army of Darkness.
The High Life / Best Friends - S2-E10
Deliberate mistake: In "The High Life", there is a scene where Stinky submerges his head in a tank of water. He delivers the line, "Gee willickers, it's still ticking", and everyone somehow understands what he is saying with his head underwater.
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."
Wizards vs. Vampires on Waverly Place - S2-E26
Deliberate mistake: Justin tells his dad he will write the idea on the white board (the theme in the restaurant/add more of an experience) yet he just scribbles, and in the scenes where you see a bit behind him, the whiteboard has scribbles instead of words where he was supposed to write.
Deliberate mistake: When Roy and Moss are in Jen's office talking about her slipping up, the computer monitor disappears from her table in the wide shots so you can see the actress.
Suggested correction: It's there the whole time. It's a thin monitor and it lines up with Roy's leg, so it might have been hard to see.
Formidable Enemy!? Mother Coordinator Enters! - S7-E37
Deliberate mistake: This Pokémon Trainer's Choice segment incorrectly claims that Arbok evolves into Seviper, which isn't true. (00:11:38)
Intermediate Documentary Filmmaking - S2-E16
Deliberate mistake: This episode is meant to be entirely a documentary made by Abed. At the end of the episode, there's a shot where the gang is looking into Pierce's window, except the camera is right in front of the window they're looking through. If Abed was filming this he would literally be right in front of the gang, completely obscuring their view through it.