Continuity mistake: When the butler takes the mother and kittens to be abandoned in the countryside he is on a motorcycle and sidecar combination. During the trip the sidecar changes from one side of the bike to the other and back again. Also, when the sidecar separates from the motorcycle when the dogs are chasing Edgar, the wheel on the sidecar switches sides regularly as well.
Continuity mistake: When Jingle, Jangle, and Mrs. Claus pay a visit to Mother Nature, Mother Nature calls her sons beside her - Snow Miser and Heat Miser. She then turns to Snow Miser and asks him to allow a little snow fall in the South, and then turns to his brother, Heat Miser, and asks to allow just "one Spring day at the North Pole." The words are correct dialog, but she should have said each of those lines to the OTHER brother. (00:39:40)
Other mistake: While the wizard is speaking near the portal, a ghost image of him appears to the left.
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)Quantom X
Continuity mistake: After Spike chases Jean-Claude out of the church, the parents and their kids stand outside. Chuckie is in his father's arms holding his Wa-wa (teddy bear). They go back inside, where Kira gives Chuckie that same missing teddy bear.
Continuity mistake: During the archery constest, in one scene Prince John has a ring on his right paw with no jewel, then all of a sudden the jewel appears. a few scenes later he has three rings on that paw, and later he has no rings at all.
Continuity mistake: When he sees Meg in the river of death, he reaches down and touches it. Then, when he jumps in, he makes a dive of at least 50 feet. (01:11:25)
Factual error: In the movie, we see the Statue of Liberty with its current bluish-green color. The statue only got that color over time, and as it was still being built, it should be its original brown.
Continuity mistake: At the start of the scene where OK arrives at the ROR house for the mid-game party, it is obviously dark inside except for flashing blue and purple lights, seen through the windows. However, when the OK gang enter the house, it isn't dark anymore and the blue and purple lights are gone.
Factual error: While bidding on eBay for the steering wheel, Vanelope tries to up the $350 bid by bidding $1,000. This scares off the real bidder, but Ralph and Vanelope don't understand how eBay works and bid against each other until they win with a $27,001 bid. That's not how eBay works. Vanelope's initial $1,000 bid wouldn't have set the high mark, but would simply have been her maximum bid in case the other bidder kept increasing his bid. The current high bid would have increased by the increment amount until it reached Vanelope's max bid. Now, it could be that the system recognized Ralph and Vanelope as separate bidders and that's why it let them keep upping the max bid. But, if the system had responded normally and simply increased Vanelope's bid to $355 with a max of $1,000, they might have realised what was going on and not started bidding randomly.