Audio problem: When Luke says, "Now all we gotta do is find this Yoda, if he even exists," if you look closely, his mouth never moves.
Factual error: The sun can't rise out of the Pacific ocean when viewed from America, as seen when Danny is playing the clarinet. (00:01:20)
Revealing mistake: There are two times in the New York battle when you can see the actors are being filmed in front of a screen: 1. when Superman kicks Non, Superman in on film and Non is hovering in front of the screen. 2. When Ursa is flying towards Non and Superman with the flagpole, she is hovering in front of the screen.
Factual error: In scenes that take place in 1912 on the porch of the hotel you can sometimes see American flags in the background. The flags in the movie have 50 stars. The 50 star flag wasn't adopted until after 1959. (01:25:15)
Continuity mistake: When the windows on Nick's truck are smashed, Elizabeth has protective gloves on when she covers her face from the glass, they are then gone when the truck comes to a halt.
Revealing mistake: When Tony is having his first fight in the embassy, it is obvious that most of his punches do not connect at all. The people he supposedly hit still react as though being hit, and the sound effects of a fist hitting a jaw are still there, even if Tony misses by several inches.
Continuity mistake: In the bullfighting scene Herbie's driver-side running board is dented upward in the middle, but in the following scene it isn't there.
Other mistake: Near the end of the movie, Dave Speed jumps onto Torpedo's private plane and starts steering it to the ground. The plane is white with obvious red stripes. However, Dave Speed is supposed to lose his super powers when he sees red.
Continuity mistake: At the beginning, when Voltan arrives on horseback at his fathers castle, it is daylight. We are then shown an exterior shot of the castle itself and it is pitch black. Then, a minute or so later, we see Hawk arriving on horseback at the castle and it is daylight again.