
Tour de Pond / Teachers Strike - S2-E18
Other mistake: Tour de Pond: When Arnold, Gerald, and Grandpa are first shown at the Tour de Pond race, their ship is not sitting on the sidewalk, but rather on the edge of it, which makes it look like it’s floating in mid-air. (00:05:02)

Tour de Pond / Teachers Strike - S2-E18
Continuity mistake: Tour de Pond: When Rex notices that Arnold's boat is winning and starts running, the red and yellow squares on his grandfather's badge change to red and black. (00:10:18)

Tour de Pond / Teachers Strike - S2-E18
Continuity mistake: Tour de Pond: When Rex's grandfather walks up to Arnold's Grandpa at the end, his badge has eight squares on it, but in the next shot, it changes to four stripes. (00:11:20)
Tour de Pond / Teachers Strike - S2-E18
Continuity mistake: The kids' teacher in "Teachers Strike" is Miss Slovak, who was their teacher in the first season, but in the first episode of this season they had a new teacher, Mr. Simmons.
Suggested correction: Other than the few episodes that take place during a specific time of year; these episodes are not meant to be taken in chronological order. Just roughly in the same 4th grade school year.
Suggested correction: I agree with the other correction, but it's also worth noting that in the production order, "Teacher's Strike" was made before "New Teacher" was. They were just aired out of order, just like many of the other episodes.

Part-Time Friends / Bio Square - S2-E19
Other mistake: Bio Square: While Phoebe and Stinky are telling the class about their science fair experiment, just as Phoebe shares that it was in honor of her hero, "I.P. Pavlov," watch as Stinky's eyes move off to the side of his head, then return to normal.

Part-Time Friends / Bio Square - S2-E19
Continuity mistake: Part-Time Friends: When Arnold and Gerald get part-time jobs at the flower shop, while Mrs. Vitello explains things to them, she asks if she's going too fast, and in the next close-up, Arnold's apron vanishes, then it reappears.

Runaway Float / Partners - S2-E20
Other mistake: Runaway Float: After Nick Vermicelli says that the parade float is a total mess, as Arnold says, "It's not a mess," the background is of the school hallway, not Arnold's garage. (00:05:28)

Runaway Float / Partners - S2-E20
Other mistake: Runaway Float: When Bob asks the kids who wants to ride on the float, Arnold says to them it's great the way it is. In one shot, Iggy's hair is incorrectly coloured black instead of brown. (00:05:52)

Runaway Float / Partners - S2-E20
Other mistake: Runaway Float: After Nick talks about redesigning the parade float, Bob asks the kids who wants to ride on the float. Arnold then tells them it's great the way it is, and when the kids start saying, "Me! Me!", there is an animation glitch where part of Robert's head and hands get stuck in the air for about a second. (00:06:01)

Runaway Float / Partners - S2-E20
Other mistake: Runaway Float: After Bob says, "Now this float has to scream 'beeper' at the top of its lungs!", as he walks away from Arnold and Helga, Joey has white skin, blonde hair, and an orange shirt. (00:06:31)

Runaway Float / Partners - S2-E20
Revealing mistake: Runaway Float: When Arnold and Gerald are watching the parade, Arnold turns his head to look at the marching band. When he looks away from it, his left eye doesn't move, and it stays visible in his hair for the remainder of the shot. (00:07:51)

Runaway Float / Partners - S2-E20
Continuity mistake: Runaway Float: When Arnold first sees the beeper float, he says, "How can they control that thing?", and Gerald is sitting on the curb to the right of Arnold. In the next shot, Gerald is suddenly behind him. Arnold is also a lot further away from the curb than he originally was. (00:08:16)
Runaway Float / Partners - S2-E20
Continuity mistake: Runaway Float: The big beeper float constantly changes appearance during the parade. Some examples: The sign saying "Let's Go Downtown" on the front changes to "Let' Go Downtown" in one shot. The sign saying "Let's Go Downtown" on the back is missing in one shot. The orange base is sometimes blue. The blue city design around the base sometimes isn't there, and it even changes colour. (00:08:17)

Runaway Float / Partners - S2-E20
Continuity mistake: Runaway Float: When the beeper float first starts to speed out of control, in one of the shots, Helga is wearing her regular outfit, not her beeper costume. On top of that, the kids on the float are smiling and waving, not freaking out like they were before. (00:08:39)

Runaway Float / Partners - S2-E20
Continuity mistake: Runaway Float: When Arnold reaches the parade float on the bike, Iggy's shirt is incorrectly coloured green instead of purple. It's also green when the float rides past Mayor Dixie. (00:09:45)

Runaway Float / Partners - S2-E20
Continuity mistake: Runaway Float: When Arnold stands up on the bike before jumping onto the parade float, Eugene's hair disappears mid-shot. (00:10:11)
Runaway Float / Partners - S2-E20
Other mistake: Runaway Float: When Arnold tears apart the big beeper on the parade float, the float's platform is missing, which makes it look like Bob and Nick are on the road. This happens again after Arnold stops the float, which makes it look like Bob and Nick are floating as a result. (00:10:19)
Helga Blabs It All / Harold the Butcher - S3-E1
Other mistake: Helga Blabs It All: When Phoebe goes inside the ice cream truck, notice how the door jumps from closed to open, with no animation at all. (00:08:34)
Helga Blabs It All / Harold the Butcher - S3-E1
Audio problem: Helga Blabs It All: When the boys hear the ice cream truck from outside, they all start running and saying, "Ice cream," but none of their mouths are moving. (00:08:48)

Helga Blabs It All / Harold the Butcher - S3-E1
Continuity mistake: Helga Blabs It All: When Helga falls from the vent opening, she knocks the telephone and answering machine onto the floor. Just as Helga notices the tape in the answering machine, the push button telephone has changed to a phone with a rotary dial. It then changes back to push button. (00:10:05)