Character mistake: When Alex mentions to Mallory that he's had sex before, he tells her he was 17 and that it was leap year. Not correct, this event occurred in 1982 (during one of the first episodes when Alex was 17), which was not a leap year.
Character mistake: Tai says "And it started to snow in the middle of July" but later you find out that it takes place on August first.
Continuity mistake: In the episode when Penny went to work with her mom and the Magician comes in with the tiger that is acting strangely. The tiger is sitting on the floor and has just eaten its food. Penny is standing there next to the tiger, the camera goes to her mom for about two seconds, then it goes back on her and the food has returned in the bowl again. Then it's empty again.
The Powerpuff Girls Best Rainy Day Adventure Ever / Just Desserts - S2-E10
Plot hole: The children decided that they hated the Powerpuff girls in one day. Then how did they have supervillain costumes and a van? The mom said they had lots of time to prepare.
Smells Like School Spirit - S1-E7
Continuity mistake: In the scene where Newt is going to measure for the "Chill Zone," he asks Cory to help him. At first Cory is holding the main piece of the measuring tape, while Newt runs out with the "pull out end." Shortly, after cutting out to a conversation, Cory is holding the "pull out end" and then releases it, so his buddy Newt is the one caught by surprise when Cory releases his end of the measuring tape.
Forever Red - S1-E34
Plot hole: Tommy states that he and the other Zeo Rangers destroyed the Machine Empire's leaders and ultimately destroyed the Machine Empire except for the Generals who escaped. This is not true - Lord Zedd and Rita destroyed the Machine Empire leaders at the end of series 4, and the Space Rangers destroyed them again in Countdown to Destruction in series 6. The Zeo Rangers never destroyed the Machine Empire.
Suggested correction: How would Tommy know that? He didn't watch the show or know the ins and outs of what happened in space. This is what he believed based on his experiences on Earth. Everything you described is factually correct, but Tommy did not witness this. So, to his knowledge, he destroyed the Machine Empire.
The Thrice Cream Man/The Flibber-Flabber Diet - S1-E7
Other mistake: In "The Flibber-Flabber Diet," Chowder and Truffles return when Mung calls them. How could they hear him when they'd already left?
Revealing mistake: The swords Jayden and Dekker use often bend when striking each other, revealing they are rubber blades and not metal.
Plot hole: In Cam's song in the dream, one of the lines is: "No fun, no sun." However, at the start of the dream, all of the Dumping Ground kids are outside in the daylight.
Continuity mistake: After the Squirmese chef sets up his additional ingredients, Corky answers the video phone. During Corky's conversation, Al's kitchen can be seen with no trace of the chef or his ingredients.
Continuity mistake: This occurs in the episode "To Each His Own." Near the end when the gang is eating chili cheese fries, the fries change from half chili half cheese to all chili, back to half and half.
Give Me Your Princess - S1-E17
Continuity mistake: Commander Keith pilots the blue lion for part of this episode since the princess is trying to learn to fly the black lion. When Keith is transported to the lion it is the black lion.
Laugh, Ed, Laugh/It's Way Ed - S1-E10
Continuity mistake: In "Laugh, Ed, Laugh", when Eddy is gambling with squirrels, he picks up a bunch of nuts, primarily acorns and only a couple of peanuts. But next shot later when he yells, "Suckers!", there are more peanuts shown. (00:05:00 - 00:11:15)
A Remedy To Cure All Ills - S1-E6
Character mistake: King Uther calls the Lady Morgana, Morgause. (00:11:50)
The Tale of the Pinball Wizard - S1-E13
Visible crew/equipment: When Russ is in the royal chair and it is moving on its own, right after it hits the witch you can see a crewman behind the chair pushing it.
Audio problem: Billie says her line "he needs a new image" without moving her lips.
Continuity mistake: When Maya sits alone in detention, the door in the corner of the classroom randomly closes itself.
El traje del tío Jacinto - S2-E16
Visible crew/equipment: In the credits, there's a unknown person hiding behind Don Ramón (Raymond).
A Single Piece Was Lost - S1-E10
Visible crew/equipment: When the Gruenaks attack the Scientist a puppeteer is visible to the right of one of the Gruenaks, just before it grabs the bird cage and throws it onto the Scientist's head. (00:28:18)