Continuity mistake: In the library scene Indy discovers the "X" high up on the balcony. The X is green with a grey background. When he breaks the tile to find the tomb the X has become a faint outline on the floor. (00:27:40 - 00:28:45)
Suggested correction: You still can see one "leg" of the X on the floor, it's only darker than viewed from above because the camera angle and illumination set used.
I think it is meant to be an optical illusion.
The "X" is first shown as a dark green "X" on a beige background. Next, we are shown the same dark green "X" that is barely visible over a green background. I think we are meant to understand that the beige square tiles were lifted away in a cut scene.
I see no reason why they would replace the floor just for the higher shot, it's the same floor throughout the scene. When they enter it's the same floor we see later as they are going into the hole. It's probably not a real marble floor, so they can use a styrofoam or plywood tile that Harrison can lift, one that matches the surrounding tiles. They don't shine as much as the rest of the floor. In the shot up high there is different lighting, so that could explain it. It just appears to be different. Of course, sudden different light can be seen as a revealing mistake.
Suggested correction: Not a mistake, just a different viewing angle.
Continuity mistake: When the Joker's henchmen are trashing the museum, one guy puts red handprints all over a portrait, later the Joker walks by the same portrait and the handprints are gone. (00:59:55)
Continuity mistake: Notice Marty's hair in the scene when he's playing "Johnny B. Goode." It's quite larger than when he says, some seconds later, "I guess that you're not ready for it yet." That's because when he says that, it's a recycled shot from the original BTTF, whereas most shots showing he's playing the guitar are newly made for BTTF2. However, Marty's hair is considerably longer in the new shots. (01:27:19)
Continuity mistake: When Spock, wearing rocket boots, is in the turboshaft carrying Kirk and McCoy on either arm, he fires the booster rockets, thus propelling the three of them up the turboshaft. If you watch carefully, the deck numbers in the background as they rise upwards go as follows: 35, 52, 64, back to 52, 77, 78, and then 78 again! Not content with one goof, Kirk and McCoy can quite clearly be seen with their feet dangling in mid air, not on Spock's boots. They aren't exactly clinging to him either, more like leaning against him. Surely Kirk and McCoy would be unable to hold onto him!
Continuity mistake: At the end of the movie, when Riggs is in the cargo area, a gunman shoots at him, he rolls and starts emptying the clip into him - you see the bullet holes in the gunman. But as Riggs is face to face with the gunman, the holes disappear.
Continuity mistake: Early in the film Bud throws his wedding ring down the latrine and then retrieves it with his right hand so it is covered with the blue disinfectant. In a (much) later scene, Bud has a blue right hand, despite not having had one in the intervening period. (01:44:48)
Continuity mistake: When Beck meets Webly on Christmas Day, Webly takes his glasses off and throws them on the desk, but in the next shot (from behind) he is still wearing them. (00:16:50)
Continuity mistake: In the scene where Belushi and Jerry Lee (the dog) enter the warehouse, Belushi askes everyone to stop what they are doing and even has the forklift driver lift him up so he can talk to them. Once he is done talking, he tells the lift driver to bring him down. The next few shots where they show Belushi walking to his car, if you look closely, you will see that the fork lift is back up in the air, but there were no sounds and there isn't another lift to be found. (00:25:05)
Continuity mistake: When Tango and Cash are playing the "good cop, bad cop" routine with Requin, the tape on Requin's mouth is almost off, but in the next shot the tape is OK.
Continuity mistake: Towards the end of the movie Dave takes Walley's jacket and uses it to help them slide down a cable. Before they slid down, Dave tells Walley to hold on, and Walley asks if they're going to be above the ground. Dave tells him no, and off they go. However, Dave is deaf, and reads lips, and Walley is standing behind him when he asks the question. So how did Dave read his lips if he wasn't looking at him?
Continuity mistake: In the scene on the plane, you see Bond hanging at the door on the right side of the plane. In the next shot, you see the plane making a left turn. In the following shot, Bond is still hanging on the right-side door. Shouldn't he have fallen into the plane?
Continuity mistake: At the end of the final match, the announcement is made it's the first time in history the defending champion kept his title. Yet in Karate Kid 1 Johnny Lawrence had already won the championship twice and was there for his 3rd time.
Continuity mistake: In the scene where they are discussing why Dalton fired Mr Wesley's nephew (upstairs in the Double Deuce). Mr Wesley's nephew threatens Dalton with a knife and when Dalton takes a swing at him, there is blood on Mr Wesley's nephew's face way before contact. (00:34:05 - 00:38:00)
Continuity mistake: When Art is eating breakfast at the Peterson's house, he takes items from the fridge. Watch when he comes back over and talks to Ray. The position of the pineapple under his arm changes from shot to shot. (00:10:40 - 00:11:25)
Continuity mistake: When Vigo throws the streams from the proton packs back onto the Ghostbusters, there is a wide shot of Egon getting thrown way over to the right. However, when they do a closer shot, he is way over to the left, closer to the other three Ghostbusters. (01:33:50)
Continuity mistake: During a car chase, the "killer" is rushing a little girl to the hospital. As they pass the sign, it reads (in English) "Scared Heart Hospital" - instead of "Sacred".
Continuity mistake: During the big fight scene at the end of the movie, both Nick and Sato become totally saturated and covered in mud. Nick defeats Sato, and is shown to have immediately arrested Sato and brought him to the police station. It is clear they came directly to the station from the fight, yet there is now hardly any mud on either of them.
Continuity mistake: When Joe Clark is having his talk with Sams on the edge of the roof of the school, Sams is on the right and Clark is on the left (when viewed from the ground). When they're done talking, Sams turns to his left and walks away - turning to his left would have made him fall off the roof after just a few steps.
Continuity mistake: In the race for King of the Mountain, Anthony wipes out and begins cursing. Then, in the next shot, he has to spit out some snow before he can curse again.
Continuity mistake: During the "exciting" conclusion, Investigator Natsuo runs toward the villain's vehicle, jumps, and kicks through the windshield. Besides the fact that there are some poor special effects at work, watch this quick shot closely. As he is flying through the air in that split second, the villain's car changes colour! It is quite obvious, as the car goes from a dark red color to dull grey.