Deliberate mistake: When Johnny is watching the news footage of the Hulk battling Thing, all the footage is merely clips from that portion of the episode, including parts of the battle that were happening before the camera crews even showed up. (00:02:50 - 00:07:20)
Factual error: When the boys are sent back to the Cretaceous era, they come across a leptictidium, a small, bipedal mammal they call "Leppy." Leptictidium were not around in the cretaceous, they didn't appear until around ten million years after the dinosaurs went extinct, in the early Paleogene. They also lived in Europe, not North America.
The Ringer - S1-E1
Continuity mistake: Zelda has an amateur magician grow a large plant for her to use as a sling shot. He is standing beside Link as it grows and then suddenly disappears between shots. There was not enough time for him to have walked or run away. (00:11:40)
Continuity mistake: When Bentley says how Maple Man can "gobble my knob", he briefly pauses between each word. When Theresa then plays back Bentley's confession, he says "gobble my knob" without pausing. (00:18:58)
Continuity mistake: The first four episodes of season two have absolutely no continuity with the show. Prime examples are the fact that Shendu exists again as a statue which had been confirmed to be destroyed in "The Day of the Dragon", the final episode of season one. Next during "The Warrior Incarnate" it is mentioned that not all the talismans were in fact present, such as the dog talisman, when all talismans must have been found, or the events that escalated during the final episode of season one would never of happened. This problem is the extended during the next episode where Jackie Chan discovers the snake talisman in some sort of Brazilian temple - he had already learned of the snake talisman by stealing it from the museum quite early on in season one. The final continuity error is that Tohru goes from friend to foe and then back to friend as if the first four episodes of season two never happened.
Suggested correction: These were "flashback" episodes, not "they never happened" episodes.
Continuity mistake: When Raven telekinetically reassembles the broken chime bead necklace, it has about nine beads and is rather tight, but before and after that the necklaces feature about 13 or 14 beads and are wide enough to fit around the others' necks.
Heads Of Beef / Klub Katz - S1-E11
Factual error: In "Klub Katz" the captian yells "Iceburg, Iceburg, on the starboard side." But when you see the iceburg and the ship, the iceburg was about to hit the bow of the ship.
Deep Metal - S3-E2
Continuity mistake: Depth Charge fights Rampage on the beach. Throughout the whole episode, Depth Charge has four fingers. But in a shot when DC doubles over in pain to clutch his wounds, he has five fingers.
Dirty Pranking Number 2 - S1-E6
Other mistake: Season 1 Episode 6: "Dirty Pranking Number 2". When the pizza delivery man shows up at the police station, the receptionist says that they hadn't ordered twenty pizzas; but the pizza man is holding only eighteen boxes.
Continuity mistake: Takumi and Shingo both have their right hands duct taped to the steering wheel, as per the rules of the Gum Tape Deathmatch. During one shot of the race, Tak's hand is no longer taped and resting casually on top of the steering wheel as opposed to the right side of it.
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.
Other mistake: When Spike is thrown out of the base by Megatron at the end of the episode, Optimus calls him 'Splik'.
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.
Bat Mitzvah Crashers/Super Secret Weakness - S1-E5
Continuity mistake: In "Li'l Orphan Happy" when Ben makes his mom the tuna salad, it has lettuce around it, but in the close-up the lettuce disappears. When it gets zoomed-out on, the lettuce is back.
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).
Mainstream - S3-E3
Continuity mistake: When Kitty goes to get a midnight snack, her hair is down. But a few shots later, her hair is up in a ponytail.
Continuity mistake: After their victory, the Turtles are celebrating and partying. Just before the episode ends, Leonardo is dancing on a white mat and doing the moon walk. It cuts to a higher angle and suddenly the white mat vanishes.
Continuity mistake: Fluttershy's neck disappears after she says, "I don't know if I can cheer enough to help her".