
Continuity mistake: After Molly tries the experiment and takes off her safety googles, they reappear and disappear randomly when she hugs Ed.

Neogenic Nightmare Chapter 11: Tablet of Time - S2-E9
Factual error: When Peter is walking Alissa home, the traffic signal at the intersection they stop at goes from red to yellow to green. Not what US traffic signals do - they go straight from red to green.
Suggested correction: Not entirely true; although they are rare and may no longer exist now, I've seen traffic lights that followed the red, yellow, green pattern as recently as the mid-1990s.
Interesting. What state (s) did you see this in? I'm assuming going from red to yellow was to encourage cars to cautiously enter the intersection in case someone was running a red light?
Traffic lights in the UK do this - it's more to give you a second to get ready, in gear, etc., then as soon as the lights turn green you can go. Otherwise you get no warning of when the lights are about to change.
In Illinois; as I said, such traffic lights are rare, but they did exist at least as recently as the time this episode of the series aired, and they may still possibly exist in larger cities such as New York City.
This traffic light set-up (red to yellow to green) still exists today in the UK. From what I understand, it is to alert the driver that the light will be turning green imminently and to prepare themselves to put their car in gear, as manual cars are still pretty common in Europe. I'd wager this light cycle was phased out of North America due to the abundance of automatic cars today. Could have been different in 1994 though.
It should be noted that traffic lights that go from red to yellow before going green keep the red light illuminated so that both red and yellow are lit up. However, that's not what happens in the scene. I've never seen a traffic light operate the way it's shown. And Massachusetts still has traffic lights that go from red to yellow, however, when red and yellow are lit up together, this allows for pedestrian crossing.

Heart of Ice - S1-E3
Other mistake: When Batman is watching the security footage of Victor Fries' accident, at first Fries is addressing the camera directly which follows him and pans according to his movements and Ferris Boyle interrupting him, which would suggest a second person was in the room with a handheld camera. But after Ferris Boyle enters the room and orders Fries' experiment terminated, there are several cuts from various angles in the room suggesting surveillance cameras. The surveillance style footage also often conveniently cuts to the face of whichever person happens to be speaking or will cut to a certain angle in order to put emphasis on the action, all of which would require multiple mounted cameras and purposeful editing by either Boyle or one of his subordinates, which would be completely illogical since they don't want anyone to see the footage in the first place. (00:12:20 - 00:13:55)

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?

Factual error: In the show Gaius wears glasses, except eyeglasses first came into use in the late 13th century while the legend of King Arthur is around the 5th or 6th century.

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)

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.

Continuity mistake: When Janet gets off the phone with Clarissa's principal, Clarissa is standing on the right side of her friend. The shot changes and she is now on the left.

Factual error: Bessie says she was going to study veterinary medicine at Texas A and M. That would have been approximately 1940. Neither women nor people of colour were admitted to TAMU until 1963 so she could not have even been able to apply.