Revealing mistake: In the opening credits, Beefy Bert has a different hair colour to what he has in the actual episodes. This was not included in Series 3.
Doug Takes a Hike / Doug Rocks - S1-E4
Continuity mistake: When Roger is dancing in Skeeter's yard, he changes color.
Continuity mistake: At the end, when Beans walks into the room Louis' hands are tied in his lap. In the next shot of Louis, his hands are tied behind the chair.
Visible crew/equipment: Oliver (a dog) jumps up on Uncle Bill's bed and starts barking at him. The real reason the dog is barking: in the shots of Oliver, the shadow of a towel or some sort of toy can be seen being waved around in order to agitate the animal. It even briefly pops into the shot a couple of times. (00:10:45)
Other mistake: When Spike is thrown out of the base by Megatron at the end of the episode, Optimus calls him 'Splik'.
Continuity mistake: The six Rangers are standing together as Wolfbane is enlarged by Orbis. Kat and Tanya change places when switching from the wide shot, to a closeup of the Rangers.
Continuity mistake: In one scene where Kris is talking to her mom, she grabs an apple, then takes a paper towel from the holder. Then, if you look behind her at the holder, it is empty. But in a wide shot, the paper towels are back again.
Batman Stands Pat (2) - S1-E14
Continuity mistake: Batman's plaster-covered costume gets an instant dry cleaning en route as he drives from the sculptor's studio to the batcave. (00:05:00)
The End of Flutter Valley (3) - S1-E3
Continuity mistake: When Reeka is conjuring the fake rainbow to distract the Flutter Ponies, the grey pot on her head is blue for a while.
Other mistake: When Don and Dr Smith are stealing Sesmar's control unit, look closely at the base of the electronic arch - Raddion is hidden from sight but the careful eye will see his golden feet.
Revealing mistake: We can see Ecliptor's zipper from behind - slightly revealing on Saban's part, considering Ecliptor is supposed to be an evil monster henchman of Astromena's.
Plot hole: It's revealed at the end of the episode that the reason Tommie was sleep walking was because he was so nervous about the 5th grade test. However, he was sleep walking before news about it was given (ie: The beginning of the episode).
Plot hole: Didn't Dexter ever notice the giant fire pit in the ant farm?
Suggested correction: This is more of a question than a mistake. (To be fair, I don't think questions were a feature yet back when this was posted.) No, he didn't. He only noticed the fire pit (and the colosseum) when he was inside the ant farm. It most likely just wasn't visible to him from the outside, or it was too small for him to see it.
Attack Of The Mutant (1) - S2-E2
Other mistake: In part 2, it was revealed that Libby was really the Masked Mutant all along but, in one scene in this episode, Libby is sitting next to Skipper while the Masked Mutant is standing on top of the bus.
Factual error: In the opening scene, the Clampetts are driving home from Malibu. From Malibu to Beverly Hills is east. But as they head home, the ocean is on their left, which means they are driving west.
Pooh's Double Trouble / Eeyore Sleeps on It - S1-E19
Factual error: The letters and symbols on the characters' reflections in the mirror look like their regular counterparts, when they're supposed to be in reverse.
Visible crew/equipment: When Mork and Mindy are walking away from the lake after they first meet, there is a set of 8 lights in two rows of four in the background.
Unicorn Club/Go Gomez! Go! - S1-E2
Continuity mistake: When the cats are entering the race the height of the sign lowers when Waffle walks up.
Continuity mistake: Just after Otis makes the ghost sounds from inside the house, it shows the gang standing together outside the house. Otis is with them outside, which is impossible, as he is inside the house pretending to be the ghost.
Fiend is Like Friend Without the 'R' - S1-E4
Continuity mistake: Mandy hits a baseball with one of Grim's bones, yet when we see Grim, there are none of his bones missing from his body.