Continuity mistake: When DeVries' Ferrari crashes into the fence, the license plate is lying crooked, touching the bumper. When the cops blow it up, it's not touching the bumper. Also notice that the petrol tank and exhausts have been removed, revealing that the car blows up by explosives rather than police gunfire. (00:07:40)
Revealing mistake: When we see Dark Helmets' hoverjeep in the desert, watch the front end: you can clearly make out the edge of the mirrored box they used for the "hover" effect.
Continuity mistake: When the statue of Liberty is about to crash on the street, a close shot is seen of jammed cars and hysterical people. When the shot changes to Superman flying to the rescue, the jam, the cops and the people have disappeared, and all is nice and quiet in Metropolis.
Revealing mistake: When Robocop is completed and they are going over his gear, they show a tracker that shows his location at all times. The tracking unit is obviously fake; the street layout is a decal and the "blip" that is Robocop is in a fixed position. (00:30:20)
Visible crew/equipment: In the scene where Derek pulls the large knife out of the alien's foot and gets blood on his face he stands up and almost falls of the cliff. To the left in this shot you can plainly see a crewmember in a dark blue shirt, probably there to jump in if an accident should happen. (00:15:20)
Visible crew/equipment: When the blob just misses Laverne, you can see a crew member under the raft (probably operating the mechanical special effect).
Revealing mistake: When Jack is hanging out of the truck you can see him standing on the hood of the car which Lydia is driving. At some points we get camera view from the back seat of the car. In some angles the mirror inside the car disappear. This is to prevent us from seeing the camera. (01:04:15)
Other mistake: When He-Man is fighting against the centurions on the floating disks, he tells the others to get inside a building. As he opens the door to the building, not only does it fall right off the hinges, but his sword also falls right off his back, pulling his cape off with it just as the scene ends. (01:09:20)
Continuity mistake: Early in the movie, Mac throws the dead green berets' dog tags to Dutch. As he catches them, Dutch has his hand closed in a fist, and the dog tags are hanging to the left. But in the close-up shot where we can read the name, his fingers are more open, with the tags resting in his palm.