Revealing mistake: In the scene where Doc Brown is following Biff into the tunnel, as Marty starts to pass between the cars on his hoverboard, one of the wheels on the rig supporting the hovering DeLorean is visible. (01:30:30)
Revealing mistake: The graphic display showing the Enterprise lowering shields is actually just a repeat of the earlier display showing the vessel raising her shields...played backwards. The giveaway is the screen still reads "Activating Deflector Shields" even though Scotty is supposed to be dropping them.
Revealing mistake: When Nick is being sucked out of the hole/cave, you can see the wires visible from his waist. (01:20:35)
Revealing mistake: When Dana is walking down one hall with Leroy and a bottle of champagne, the exit sign is reversed. (00:53:05)
Revealing mistake: When the main guy is fighting the main girl in his room, the scene changes angles and you can CLEARLY see that her stunt double is a man!
Revealing mistake: When Ray, Winston and Egon are underground looking for the river of ooze, there is a scene where they break down a small wall of rocks. Ray then sits on one of the rocks and it bends under him - it's rubber or foam. (01:01:50)
Revealing mistake: At the end of the movie when they reach the surface, you can see that the horizon is nothing but a big wall with the sky painted on it. You can see the water splashing up against the wall.
Revealing mistake: When Beth is helping Martin out of Bartok's cocoon, you can see Martin wearing pants inside the cocoon. Surely he should be naked. (01:35:15)
Revealing mistake: After the water tentacle sequence, Coffee brings Schoenick back to their bunks to get the submachine gun, so they can take over the rig. The bag containing the gun is stashed behind some pipes up by the ceiling. Watch when he reaches behind the pipes to grab the bag--the pipes move at least six inches. (01:31:57)
Revealing mistake: At the end, when all the historical figures are going back into the phone booth, you can see the trap door in the back open and the people go through it. It would be kind of tight to fit all of them in the booth at the same time.
Revealing mistake: When little Melvin gets turned back into Toxie, Toxie charges towards the devil and picks him up, and starts swinging him up in the air. While he's doing that, you can tell the devil has been replaced by a very unconvincing dummy.
Revealing mistake: Near the end of the movie, when Wallace says: "hold tight lad, and think of Lancashire hotpot" one picture of a sheep on the ceiling slightly moves a few times. (00:19:57)
Revealing mistake: In the dream sequence while Bruce is now the Hulk, if you look closely beneath his green wig, the black hair of the actor is visible.
Revealing mistake: The bad guy that Nady punches and falls through a hole is a very obvious mannequin. Watch for the close-up of the hand.