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.
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.
Delenda Est - S3-E11
Revealing mistake: When Dylan and Tyr head to a bridge where supposedly the power source is located as well as Rommie, they start to cross the bridge. As the camera is facing Dylan and Tyr, the next scene two aliens teleport in. Rewind the video to facing Dylan and Tyr and play in slow motion. Watch the bottom portion of the screen and notice the top portion of one of the alien's head go into the camera as if the aliens walked into position for the teleportation.
The Best Years of Your Death - S1-E3
Plot hole: In the chapel, you can see the heads of those who tried to cross Harriet (the mad matron) preserved in formaldehyde. How did she get hold of so much of it? Wouldn't her husband or the headmaster be suspicious?
Episode #1.2 - S1-E2
Other mistake: The very first word of the opening title contains an embarrassing typo, considering it's the name of the main character: It reads "Maud'Dib", instead of "Muad'Dib".
Other mistake: After they arrive in Marina Bay the pink ranger is wearing the red ranger's jacket.