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: In the first BTTF movie, when Lorraine and Marty are sitting in the car, Lorraine takes off her coat and then asks Marty why he's so nervous. In this movie, when Marty is crouching down to get past the car, Lorraine looks at 1955 Marty and asks him why he's so nervous without taking off her coat.
Continuity mistake: In the beginning when Doc takes Marty and Jennifer to 2015 for the first time, they are descending towards Hill Valley. Doc turns the steering wheel to the left but the car goes right and down. (00:05:53)
Continuity mistake: When Marty is at the dance and the Marty of 1955 is on stage is about to sing Johnny B. Goode, you can hear the 1955 Marty saying "this is a blues riff in B, watch me for the changes and try to keep up" through the microphone. In the original, Marty looks away from the mike when he says this and is unamplified. (01:24:25)
Continuity mistake: In the part where Marty is trapped in Biff's garage, Biff's rear view mirror on his car is at the very top of his windshield. Later on when Marty is holding on to the car with the hover board the rear view mirror is in the middle of his windshield. The rear-view mirror was lowered about six inches or so. (01:10:12)
Continuity mistake: In the Café 80's just after you hear Marty say, "It is Wild Gunman", notice the three people sitting in the second booth from the back wall. When the scene changes to Marty throwing his hat on top of the game, you can see that the people have changed tables. You can also see that they are gone again when it shows a close-up of the two kids. (00:15:18)
Continuity mistake: In the scene where the 1985 Jennifer is in her 2015 home and says "I get married in the Chapel-O-Love?" right before she picks up the picture note the Chapel-O-Love picture and frame on the bookcase behind her. After she picks it up and drops it leaving it on the floor she looks for a place to hide. Later on when the old Lorraine and George are in the living room, take another look at the picture on the bookcase; the Chapel picture is set back up. You could argue Lorraine would have had enough time to set it back up. But look at the Chapel picture; it's inserted in the frame upside down. You can tell by looking at the frame stand behind it. Meaning someone physically removed the picture and put it that way. (00:28:18)
Continuity mistake: When Marty is in Mr. Strickland's office trying to take back the almanac, it shows a wide view of the office with two flags right next to each other. After cutting to a close up view of Marty they are apart, then Marty moves them together. (01:19:20)
Continuity mistake: If you look very closely, after Marty flips on the little girl's hover board and is laying on his stomach, when he goes to get up you can see that he's wearing regular lace style tennis shoes and not the auto-lace high tops that Doc gives him as soon as they get to 2015. You may need to pause it to see them. (00:18:56)
Continuity mistake: When Biff is trying to get Lorraine to go to the dance with him, (the bit when Lorraine is looking at her dress) you see the same extra walking past her about three times. (01:06:07)
Continuity mistake: When Marty avoids Griff and his thugs by jumping in the water off his hover board, his hair gets wet. After his coat dries his hair he rubs his hand through it. It gets all messy and crazy and uncombed. The very next shot shows him talking to the girls with perfectly combed hair. (00:21:33)
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)
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)
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)
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.
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)
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.
Answer: He is attempting to play the song "The Power Of Love" by Huey Lewis and The News. He was first seen playing it very well in the first Back To The Future movie when he was trying out for the school dance. Jennifer recognizes the song and is shocked that Marty who was so good at guitar was suddenly able to hardly play it.