Deliberate mistake: The tattoo on Mr. Funktastic's chest actually says Mista Fuktastic, not Mister Funktastic. (00:19:30)
Deliberate mistake: When Brian and Bilkins are at the demolition derby, Roman wins and gets out of his car. As he scans the crowd, he sees Brian. When we see Brian the logo on his shirt has a 3D effect to it that goes back and to the left. In all other shots of that logo, the effect goes back and to the right. This shot is reversed.
Deliberate mistake: A lot of the supposed handheld footage from bystanders on the scene couldn't have been filmed as such. People are on the ground, but the handheld footage is close to the action, as if the bystander is right there next to the action. This is a common mistake in a lot of movies.
Deliberate mistake: During the car chase in the Cadillac, the van being chased crashes through a concrete block wall. Even if you can look past the unlikelihood that the van would even be drivable after going through, it is impossible that it would come through without any damage. Surely the windshield would be cracked, the headlights broken, etc. This was obviously not done with a real brick wall and they didn't think to damage the van before running it through the wall. They do show a dent and a messed up grill in a closeup later, but the damage doesn't match the wall scene. (01:02:10)