Continuity mistake: Rumplestiltskin looks completely different in this movie than he did in the previous film Shrek The Third; Prince Charming momentarily talks to Rumplestiltskin in the tavern during the third film, and the character looks completely different, has a different voice and different demeanor.
Continuity mistake: During Andy's daydream at the beginning of the film, Mr. Potato Head has an eye patch over his left eye. When the daydream cuts back to reality we see that Andy has removed Mr. Potato Head's left eye to symbolize the eye patch. But when Andy's mum comes in with the video camera, his left eye is suddenly back in. (00:01:15 - 00:05:25)
Continuity mistake: Gamble and Hoitz get thrown to the ground when the accounting office explodes. In an overhead shot of them rolling around on the ground, Gamble's wooden gun has fallen from its holster and is lying on the ground. Cut to a side shot and the gun is back in its holster. Gamble had both hands covering his ears the whole time, he did not pick up the gun. Then comes another overhead shot, the wooden gun is again missing from the holster.
Continuity mistake: When Rapunzel wraps her hair around Flynn's hand she does so six to seven times. When the camera pans to the hand, it shows a criss cross pattern. That would require at most, 2 or 3 times, of wrapping the hair around.When the glow of the hair reaches Flynn's hand, the hair is wrapped in a straight formation. Then when the hand is healed Flynn unwraps it, with no more than one to two revolutions of wrapped hair.
Other mistake: When Gregory has read the note from Fregly, he realises he put his thumb on a booger. When we see Greg on the floor, the note should be nearby. Instead it is several feet from him, in line with the bin. This is strange as Greg only dropped it and the note didn't flutter over there as Greg only turned when he hit the floor. In fact, the movement should've moved it closer to him. In line with the bin is even weirder.
Continuity mistake: In the dock scene where Rob Schneider kicks David Spade in the groin the first time for supposedly sleeping with his daughter, his good foot has a black shoe on it. Then as you see him kicking Daid Spade he has no shoe but is in bare feet, But when he falls down from the pain in his bad foot you can see that he now has a black shoe on his good foot again. (00:11:45)
Plot hole: When Astrid gets on Toothless for the first time, Toothless takes off uncontrollably and tries to scare her. Hiccup seems to have no control over him at this time. How is that so if with the new tail fin, Toothless cannot fly without Hiccup's precise control of the tail fin? That whole sequence would have fallen apart. This mistake was even admitted to on the DVD commentary. (00:53:35)
Factual error: Milo gets out of the car to pump gas, but they are in New Jersey where pumping your own gas is illegal.
Continuity mistake: In one of the final scenes of the movie, George Lopez and his wife are depicted on swings with two red wines placed on a table. The scene transitions into another couple and later George Lopez and his wife are shown again. This time they toast and drink the wine on their swings. However, in this scene the wine they are drinking is white.
Continuity mistake: When passing the lion in Trafalgar Square approx one hour in, the motorcycle sidecar swaps sides.