Continuity mistake: It's established that in the candy cane trees, the double striped branches 'break'. When grabbed, they make a loud noise and flash for a moment, before just vanishing. When Ralph and Vanellope are racing to the Hero Metal at the top of a tree, Ralph hits several of these branches. Each time, the branch only lasts about a second or two after he touches it before vanishing. However, he then falls from the tree and lands on a branch that is double striped and hangs from it. While doing so, he proceeds to have a full on conversation with Vanellope, for a relatively long time. Yet the branch does not vanish till after she walks away, despite previous ones having only a second or two of time before vanishing.
Character mistake: When the Sugar Rush racers are throwing in their gold coins to enter the Random Roster Race, the announcer can be heard reading the name "Adorabeezle Winterpop" third, after Taffyta Muttonfudge, and "Crumbelina Di Caramello" fifth, after Gloyd Orangeboar. But the next time the roster board is shown, Crumbelina's name is printed on line 3, while Adorabeezle's name is on line 5. The board's order may be considered the correct one, as not only does the same order appear on it again as the race commences, but Crumbelina can be seen lined up right behind Taffyta just before they begin to toss their coins to the pot.
Continuity mistake: When Deanna begins to pull Felix onto the dance floor, she is wearing a shiny dress imprinted with leaves and flowers. When they take their places in the next shot, Deanna is suddenly in a plain pink dress, with no imprints. Then, although she remains on the dance floor for the entire shot, when Gene answers Felix in the very next shot, Deanna is suddenly with Gene by the door, and she's back in the dress with the shiny imprints for the rest of the scene.
Continuity mistake: When Felix calls Calhoun a "dynamite gal" she has a flashback of her former fiance calling her a dynamite gal. The last time he called her a dynamite gal, it was at the wedding. He only manages to say "dynamite" before the cy-bug bursts through the window and he gets eaten by the cy-bug. However, during the first flashback of Calhoun's former fiance before she and Felix enter Sugar Rush, it shows the former fiance getting eaten by the cy-bug at the wedding, but he didn't say "dynamite gal" before he was eaten. Also in the first flashback, their arms are by their side. But in the second flashback, their arms are interlocked with each other.
Continuity mistake: When Ralph looks down on the entrance of Sugar Rush after being lifted by King Candy, you can see the path is empty between the three characters and the cybugs. But when Ralph frees himself from King Candy's grip and Vanellope starts glitching towards Ralph, you can see Calhoun's discarded weapon lying on the ground. Something so distinctly black would stand out on the rainbow bridge from a distance.
Deliberate mistake: When Felix is about to receive his first medal, a few things change in a cut to a close-up. The building has grown much wider (32 notches under the roof compared to 22 before), giving the Nicelanders room to carry Ralph before throwing him, when previously Ralph was already against the edge. Additionally, a pair of large clouds has popped into the middle of the screen to cover the medal before it appears, which may have been considered too distracting to include in the previous shot. Later on, the medals which are engraved with Felix's name in-game instead bear a bas-relief hammer and gain a white stripe through the center of the ribbon when shown in 3D, a rather drastic change for what is only meant to be a view in greater detail. (Official recreations of the game work around the first issue by reducing the distances covered by objects on the roof to begin with.).
Deliberate mistake: When Ralph and Vanellope are practicing driving, Vanellope loses one of her upper teeth. The tooth magically reappears again for the rest of the movie. Most noticeable when Ralph rescues her from the dungeon and twice noticeable when she is doing the race. First when she says "I'm gonna win" before starting the race and second when she overtakes King Candy and is in the following tunnel.
Continuity mistake: When Calhoun and Felix are in Game Central Station getting ready to enter Sugar Rush, one of the portals behind them is displaying the words "Now playing Burger Time," meaning the game is in progress. But shortly afterwards you can see Peter Pepper, the main character from from that game, serving what looks like a pie to the characters from Q-bert.