Continuity mistake: Episode 66-5 "Hassle In The Castle/Remy Rides Again": In the final scene, notice the house across the street furthest to the left; first time it is shown there is a large window with light coming through. The last time we see the same shot, however, it is a totally different house.
Continuity mistake: Episode 4-6 "The Jimmy Timmy Power Hour": In the scene where Timmy and Cindy are in the Candy Bar their milkshake has two straws for the first two shots. But in the next shot there's only one straw which is on Timmy's side, it then moves to Cindy's side. Then when Carl, Sheen, and Libby run in both straws appear again. When they all run out there's only one straw and on Timmy's side.
Continuity mistake: In the Fairly Oddparents episode "Power Pals", when one of the Power Pals chucks a crystal into a drain to create "The Table of Frienditude", the crystal bounces under a table and into a drain directly under said table. However, when the shot pans out, the drain is beside the table, not under it.
Continuity mistake: In the season 3 special "Fairy Idol", Norm looks at various newspaper clipping about how bad Bucky McBadBat is. One of them says "Worse Baseball Player Ever" when it should really be "Worst", and when Norm hands the paper to Chester later, it suddenly does say "Worst".
Continuity mistake: Real 4-3: Baby Face/Mr. Right: When Timmy first finds the place in the license plate maker where you stick letters in, there were 7 slots, but later when we see him spelling "I wish I was ten", there are 12 slots, enough to fill in that sentence, without the spaces.
Plot hole: Timmy uses his heat vision, that he previously wished for, to win the race for his future dad. But it's revealed later in "Smarty Pants" that if you use a previous wish in a contest, it is magically taken away because it's cheating.