Revealing mistake: There are several instances where you can see that the bandages used to wrap up the girls are pre-assembled. When the first girl is "waxed" you can see there are no joins between the bandages, they are all in one piece - almost like a body stocking. You can also see this later with Elizabeth, and it becomes more significant because you see the bandages being wrapped around her head as normal, and then when Watson pulls them off, they come away in one piece like a balaclava, which of course shouldn't happen.
Continuity mistake: When Taran, Princess Elonwy and Fflewddur try to escape from the Horned King's castle, Taran opened the gate by removing the chains. The next shot the gate is closed and chained, the last shot the gate is open again, and the boat is pushed trough by Taran. (01:06:33)
Revealing mistake: Just before Michael and Ellie get out of his car, a fire extinguisher is seen mounted above the dash. Michael opens the hood and the engine begins smoking. Michael reaches into the car for the extinguisher. You can see through the windshield that he is handed another extinguisher instead of removing the one from its mounted spot. The mounted extinguisher is still visible in its holder. Likely done to preserve pacing so he doesn't have to fumble with the clamps on the mounted one.
Continuity mistake: When Wolfgang first gets trapped in the bubble, he says it's air tight, and he cannot breathe. When Ben goes into the bubble to spy on Lori, he's in there for several minutes and has no trouble breathing.
Continuity mistake: Everyone wears the same outfit during their hunt for Big Bird. Maria's changes to a dress once they arrive in Toadstool.
Visible crew/equipment: During the final battle, when the Ewoks swing on the ropes, a crew member's hand is visible pushing one of them forward.
Other mistake: When Dagg hits the soldier on the left while the fembot is distracting them, he falls over and the one on the left turns to see what happened. It then cuts to a different view and suddenly the second soldier just falls over without even getting hit.
Factual error: Quatermain and Jessie are on the roof of the caboose of the train. The train engineer slams on the brakes because there are elephants on the tracks. Instead of being flung forward as the train slows, Jessie is flung towards the rear.
Continuity mistake: The judge arrives and tells the audience that they can sit down. The guy on the left with a white linen shirt sits and crosses his left leg. Reverse shot, and he is repeating the action, this time crossing his right. (00:03:20)
Continuity mistake: When John Candy is woken up by his wife after getting drunk with Scully, he has a hoop earring in his right ear. Later during the regatta, the earring appears in his left.