Revealing mistake: There is an obvious stunt double for Grandpa during the fight scenes.
Revealing mistake: When Tim Curry runs out of Kevin's hotel room after being scared by the inflatable clown doll he hits his knee on a table. When he hits the table and then hops away you can clearly see that he is wearing a knee-pad.
Revealing mistake: During the ghost of Christmas present, Kermit is walking with tiny Tim on his shoulder and you can tell Kermit is walking on a spinning drum. Right before the camera pans away you can see Kermit's feet slide like he stopped walking but the road kept spinning. (00:55:00)
Revealing mistake: When George Newton comes into the house and it is raining he has an umbrella in his hand. If you look outside his door underneath the balcony it's wet, but further down the path the ground is dry.
Revealing mistake: In the scene where Sarah (David's sister) punches one of the Delaney brothers after being harrassed in the alley, she draws back to throw a punch. She first bangs her hand on the brick wall then, after she throws the punch, she punches the other brick wall extremely hard. You can see her bend over whencing in pain and grabbing her hand right before they switch camera views. When they switch camera angles, she's no longer crouched over and she's obviously had time to recover. (01:37:15)
Revealing mistake: While Nick and his father are driving home with the giant baby behind (an obvious green screen projection), the baby breaks a tube from the car and throws it to the floor. Nick bends down to pick up a prop located offscreen, to add up for realism, but the problem is that he bends down before the baby throws it, so the whole trick is revealed.
Revealing mistake: When Gazeem is standing in front of the Cave of Wonders, he leaves no footprints in the sand.
Revealing mistake: Toward the end of the film, there's a scene were Dick hits a Spango soldier and Dick shakes his hand in pain. If you look over his right shoulder, you see two people fighting but there's no physical contact being made.