My Journey - S3-E2
Revealing mistake: When Elliot is splashed by the dolphin, if you watch carefully you can see her hair is already wet.
Remy Rides Again/Hassle in the Castle - S5-E10
Revealing mistake: In the episode Hassle In The Castle, in the hall of Infamy the name plates are either scribbles or they're just blank.
Revealing mistake: In the opening scene when we see Jack and Victor as small boys and then turning into old men, look at Victor when he is a small boy. At one point he looks at the crew. It is over in a split second. Blink and you will miss it.
Revealing mistake: If you look at Les out of Les Alano's' drumming, several time throughout the whole show, you can see he is miming and his stick is not even close to the actual drum.
Revealing mistake: When the school bus is shown cruising around the corner on the way to the camping area, you can see that as it turns the corner is is virtually empty. (01:38:50)
Skating Away - S2-E2
Revealing mistake: When Van falls from the roof, you can see that the backdrop gets hit and starts to move.
The Terror - S1-E9
Revealing mistake: When Captain Liberty writes The Terror's phone number on the napkin we can plainly see that she is using a blue bic ballpoint pen - but when we get to see the napkin she had written the number on (again - second napkin) it was written by a felt-tip marker.
Revealing mistake: When Mr. Klimer is forcing Debbie into the Oblong's car, her arms disappear for a single frame.
Christmas Special: Part 2 - S3-E2
Revealing mistake: Many shots show the trees and bushes in full bloom despite the fact it's Christmas. Most notable is the tree outside the pub window in Brent's second date and the bushes outside Brent's window when he's driving around in the daytime. Acknowledged in the DVD commentary.