Deliberate mistake: When the bear pulls Woody into the garbage bin after the other toys have crossed over, his hat is not pulled off when his body is squeezed under the lid when going down. (01:15:35)
Deliberate mistake: There was no possible way for Edith to still be alive after the spiked coffin closed in on her. There are spikes on the doors and at the very back and sides of it, and she couldn't have squeezed in to brace herself. Probably done for obvious reasons, but still a mistake nonetheless.
Deliberate mistake: When Metro Man flies towards the observatory to save Roxanne, we see a typical "the-characters-see-what-the-audience-sees" shot - a Super-Man-esque shot of him with his arms stretched out in front of him with his fists clenched. This shot is then projected onto a monitor that Minion is watching. It would be impossible to achieve this. It's as if there's some sort of camera on top of the observatory filming Metro Man, which there isn't. We see the observatory enough times to see that there isn't, and even if there was, the angle at which it would need to be at would be impossible to achieve. The shot of Metro Man on the monitor is positioned right in front of him, panning backwards. A camera would need to be very long to achieve this kind of shot, but there simply isn't one present.