Revealing mistake: When Woody falls out of the closet wrapped in the string lights he hears Buzz's voice, and in the next shot as Woody sneaks up to Hannah's room we see Sid's open door and doorway, which looks perfectly normal. However, after Woody rescues Buzz from Hannah's tea party they both stop in the hallway, and there's another shot of Sid's open door and doorway, only this time it's not normal to say the least. Five of the six hasps, bolts, and locks that should be (and normally are) screwed into and attached to the inside of Sid's door (one hasp mechanism, third one down from the top, is attached to the door's frame) are now actually kind of floating there in mid-air right beside the doorway, as if there's an invisible door there. Weird that Pixar artists deliberately did this, but it's bizarrely funny to see.
Continuity mistake: When Mr.Incredible lands on the island, he gets stuck in his capsule, eventually smashing it to get out. He starts stretching, bending backwards. The angle lowers to show that Mr.Incredible suit is now a two piece, revealing his fat belly. During the rest of the movie the suit is a one-piece, so this wouldn't be possible. (00:35:15)
Continuity mistake: After Dory reads the wall map while she's in the glass carafe, when Hank hides behind the rolling cabinet there's a long shot of the corridor with him at the far wall, then in the next shot from behind Hank a drinking fountain has suddenly appeared on the wall to the left between two pictures.
Continuity mistake: After Chuckles tells the story of Lotso we see the gang locked up at the daycare center. Jessie comforts Bullseye and looks at the word "Andy" on her boot (with the "A" on the inner side) . Woody returns and when the bell rings for the kids to go outside, we see Jessie on the floor. Notice that the "Andy" on her boot is now different (the "A" is on the outer part of her boot). (00:52:50 - 00:57:10)
Other mistake: At the start of the film when the commentators are explaining the tie situation between the 3 cars the green arrow to the car is out of alignment and misses the car, instead pointing at the track.
Continuity mistake: After the old lady thanks Dash for saving her from getting crushed by the flung blue vehicle, that vehicle suddenly has been moved slightly to the left from its original landing spot. Also, another wrecked light blue vehicle was visible as the aforementioned blue vehicle hit the ground, after the old lady thanks Dash, it has suddenly been replaced by a white wrecked vehicle instead. (00:05:45)