Continuity mistake: After Ralph destroys the cake and it goes all over the place, we cut to a wide shot. In this shot, to Gene's right, there is a small amount of cake on the floor. In the following shot, the amount of cake has doubled. Also after Ralph destroys the cake Mary is holding the people that were on top of the cake even though Ralph just destroyed them. (00:13:10)
Other mistake: During the cast in the credits, 1st Commercial Guy is misspelled. They put "1st Commerical Guy."
Plot hole: When Dex is rescuing the baby kittens from the Fat Cat Burglar on the hot air balloon, whilst it is flying over the city, the four hairless hamster henchmen fly off the balloon and plummet down onto the street. Dex then saves the baby kittens and lands in the park, where two of the henchmen are shown landing in the park after plummeting. Three problems with this. 1) The henchmen fell before Dex saved the kittens and made his way down to the park, so how did they land on the ground long after Dex landed on the ground? 2) How did they land in the park if they plummeted from above a street? 3) How are there only two henchmen shown landing when four of them were shown falling all at once? (00:04:30)
Continuity mistake: At the end of the movie, before the Guardians leave, Jamie rushes over to hug Jack. In the first shot, the top of his head nearly reaches Jack's ribcage. However, in the following close-up shot, Jamie is almost at the same height as Jack's shoulders. (01:27:30)