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.
Revenge of the Bog People - S2-E2
Continuity mistake: When Doleman is roleplaying with McKern, initially the chains are properly attached to his handcuffs. But when they start talking about spikes, he's holding the chains in his hands.
Continuity mistake: Rev Bem returns for this episode, however the costume department seems to have forgotten all the changes his character went through a couple seasons ago. His face is distinctly more Magog than it should be, and his hands have reverted back into clawed fingers.