The Origin of the Fantastic Four: Part 1 - S1-E1
Other mistake: When Puppet Master is making a clay figurine of Thing, the mold he uses doesn't have a Thing-shaped interior with which to make a detailed figurine. The figurine should have just looked like an undefined human-shaped figure. (00:15:20)
Other mistake: Spider-Man is shown web-slinging past several glass buildings, but he does not cast a reflection in any of them. (00:00:10)
Other mistake: When Tony and Julia and the two tailing reporters walk past the press, they appear out of thin air. They should have either appeared from the courthouse door, which is closed the entire time, or from the left side of the screen. Instead, they appear on screen from just behind the reporter in the foreground, who is not obscuring enough of the screen for Tony and Julia to have gone unseen up until that point. (00:10:03)