Revealing mistake: While Andy, Aunt Bee, and Opie are at the Hollywood studio watching a scene being filmed, when Andy mistakenly stands up and interrupts the filming we can see the wall and shelves behind the director, and it should look familiar because it's the wall and shelves from Floyd's shop in Mayberry.
Super Grover
Revealing mistake: When Laura picks up Baby Rose from Thomas Stark, the blanket is flipped up and you can see a plastic doll's leg, then when she goes into the bedroom, she has the real baby.
Welcome to the Family Part 2 - S2-E25
Revealing mistake: When the family releases Chloe's bubble ability for the last time in the episode the bubble machine is visible.
Revealing mistake: In "Not Normal" when SpongeBob says "Hmm. This video tape should help," his left arm is missing. (00:01:25)
himan
The Way We Almost Weren't - S2-E23
Revealing mistake: Closer to the end of the episode, when Lilly and Oliver are lying on the floor glued to the chairs, you can easily see black strips on their backs attaching them to the chairs.
Revealing mistake: In SPD Episode "Sam Part 1" (13-7), when the Ranger first yells "SPD emergency," a piece of Jack's Morpher breaks off.
Double, Double, Toil and Trouble - S4-E4
Revealing mistake: As Serena gets hit by the pie her real blonde hair shows underneath, also, she wears minimal make-up for the only time.
Revealing mistake: When Arnold's burns down you can see the set walls wobble a lot.
The Fresh Prince Project - S1-E1
Revealing mistake: When Will staples his Malcom X poster to the wall, the wall bends back and forth for a second or two.
Revealing mistake: Carly, Sam and Shelby all corner Nevel in the ring. If you look in the corner where Shelby shows up, she's not in that corner until the light flashes on her.
Revealing mistake: When Peter is on the trampoline, instead of saying "Peter," Carol says, "Go get 'em, Chris!" and a few minutes later the same thing happens after Cindy has a turn alone, you can hear Greg say "Why don't you give it a try, Eve?" (00:18:10 - 00:19:50)
Clash!! Sonic VS Knuckles - S1-E5
Revealing mistake: Right at the end of the episode, when Amy is telling Knuckles he should apologize, Amy has two right hands.
Revealing mistake: In almost every episode where Michelle is a toddler, you can always see her look to the right or left to most likely a person telling her what to do.
The Library - S1-E3
Revealing mistake: In the extra 'Library' scene, the book that Bean is given already has the loose pages before he has been at them with the knife. (At one point the pages get pushed forward a little bit, meaning that they're not fastened into the book.)
Revealing mistake: When Shannon walks into the kitchen and gives Stephanie a hug, in one shot of the highchair where Tommy is sitting there is now a doll.
Bowling255
Revealing mistake: In the wizards versus werewolves special, it's painfully obvious Juliet is a stunt double when she fights and grows her wings.
quite big
Remy Rides Again/Hassle in the Castle - S5-E10
Revealing mistake: In the episode Hassle In The Castle, in the hall of Infamy the name plates are either scribbles or they're just blank.
The Joker Goes to School (1) - S1-E15
Revealing mistake: Batman drives out of the batcave alone. The first bit of stock footage of the car leaving the cave does indeed show him alone in the batmobile. But the very next stock shot of the car speeding down the dirt road shows us Robin sitting in the passenger seat. (00:05:25)
Jean G
Revealing mistake: When Topanga is "naked" under the cover, at one point, you can see a large corner of her bra.
Revealing mistake: When Josh is telling Drake that Mindy told him she loves him and when Josh slaps Drake near the end of the scene, it is really obvious that Josh is slapping air. His hand is at least 6 inches away from Drake's head and yet they play the sound effect for a slap.