Audio problem: After Doc and Marty return to 1955 in an effort to steal the almanac back from Biff, they land the DeLorean. Doc says, "Here's some binoculars" then says "and" but watch his lips as he says "and", it just doesn't match. You could argue that it is a bad angle but even at the angle it's at, you get an OK view. (01:03:05)
Continuity mistake: In Biff's apartment in alternate 1985, while Biff and Lorraine are arguing, he knocks her to the ground and both her shoes come off. After Biff punches Marty in the stomach, it then switches again to show Lorraine's reaction. As it does this, we see her on the floor but her shoes are back on her feet. She could have had enough time to put them back on possibly, but it seems unlikely that she would have done so as she is lying in the same position as when she was knocked down. (00:48:18)
Visible crew/equipment: If you look at the money case that Doc brings with him that has all the different types of money for each year, you will see where it says 1864 the reflection on the glass or plastic of what appears to be a tripod most likely for lighting. (01:03:47)
Continuity mistake: When Biff punches Marty in the stomach, he falls to the ground between Biff's henchman. The camera angle changes to a wide shot and Marty is still on the floor but he's about 3 feet in front of the henchman now.
Continuity mistake: Biff has exactly the same view towards the street as Marty and Jennifer, but the houses and cars on the other side of the street are totally different. (00:02:26)
Revealing mistake: When Biff cocks his revolver in the alternate 1985, you notice that the chambers rotate in the wrong direction. This is either a flipped shot or a mistake caused by the prop gun.
Revealing mistake: As Doc and Marty go to the soon-to-be Lyon Estates in 1955, the DeLorean hovers over the camera. Look at the roof. You can see 3-4 wires attached to the time machine.
Continuity mistake: Before Griff shows up in the cafe, the Pepsi bottle's label is facing the counter. A second later, when Griff appears, the label is facing the door. (00:14:47)
Revealing mistake: When Marty, in the 1955 dance, looks at his father with his binoculars, you can see that the angle of the binoculars are really misplaced. Marty is looking at him at his far front, but the binoculars' image comes more from the floor. In fact, what the binoculars show is from the first film. (01:15:19)
Revealing mistake: When Marty goes to burn the almanac he flips the hover-board to his hand. The board begins to flip up before Marty touches it and even so, he doesn't touch it at all, he steps his foot behind it. (01:35:19)
Continuity mistake: At the clock tower scene at the end of the movie, you can see the DeLorean drive past a line of shops that are about 25 yards from the clock tower itself. However, in the next shot of the DeLorean, you can see that it has only gone about 50 yards from the Bluebird Motel (where it started from). In addition to this, even if there were some identical shops further up the road that Marty went past (which there more than likely aren't), you can't see any on the next shot. These shots are chronologically incorrect.
Continuity mistake: When Marty gets the sports almanac in the tunnel, he flies on the wall with his left foot in the hover-board's strap. When he flies over the car and lands on the hover-board, his right foot is in the strap of the board. After that it keeps switching legs and in or out of the strap. (01:33:00)
Continuity mistake: In the beginning of the movie, when they reenact the last scene from the first movie, Marty asks Doc how he's going to turn out in the future. Doc pauses briefly, then says "No no no, you and Jennifer turn out fine." He doesn't pause in the first movie.
Plot hole: After Biff steals the DeLorean and travels back to 1955 with the Sports Almanac the movie states that he creates an alternate timeline. Doc Brown does a good job of illustrating this on a chalkboard. So if, as Doc Brown states, Biff created an alternate timeline, then when he travels back to 2015 it would be the alternate 2015. Even if the original timeline stays intact with Doc and Marty in it, they'd be trapped there because Biff took the Delorean and returned it to the new timeline, not the one they're in.
Continuity mistake: In the scene after Marty is leaving the school hall after his performance, Lorraine and George bump into him backstage and Lorraine says, 'Marty that was very interesting m... music' with a stutter. However in the first film when she says the same line in the same scene she says it without a stutter. It is meant to be exactly the same line and scene from the previous movie. (01:27:53)
Other mistake: When Doc, Marty and Jennifer have arrived in 2015 Doc tells them that the time of the day is 4:29pm. However the destination time is still shown on the time circuits' display from their time travel to the future - the two times should match, but the destination time has the bottom AM/PM light illuminated, while the current time has the top one lit. They didn't arrive or leave at 4:29am, so something's wrong somewhere. (00:04:42)
Revealing mistake: When the DeLorean is flying behind Biff's car, you can see the wheels of the DeLorean rolling along the ground. This is evident when the car turns to fly away after Marty is deposited on the back of Biff's car. (01:30:28)
Revealing mistake: When the Doc of the future is in 1955 and sees the DeLorean, his hair is short (in fact you can see that the actor is wearing the wig that he wore for the 1955 Doc), but after a shot to Marty and back again, his hair is the same length as it was in 1985. (01:12:26)
Continuity mistake: At the end of Back To The Future, when it shows Marty and Jennifer talking to Doc, Marty is tanned, but at the start of this movie when the scene is repeated, he is pale.
Continuity mistake: When Doc Brown lifts off in the Delorean just after Marty gets the Almanac from Biff, Doc does a full right turn on the steering wheel, but the next shot shows the Delorean turning left in the air.
Suggested correction: When Doc explains to Marty the events that changed the timeline from 1955 onwards, several hours have passed since they returned from the (original) 2015. Old Biff likely returned to the original 2015 not long after after giving young Biff the almanac, so it is entirely plausible that not enough time had passed for the alternate version of 2015 to take ahold. When Doc tells Marty if they were to go back to the future they would be going to an alternate future, enough time had passed for the future to turn into the alternate future.
Casual Person