Continuity mistake: When Marty first enters the Cafe 80's you can see behind him the two kids playing the working video game. The next scene that shows them the kids are still playing the game. However the third time you see the game it is now off with no kids in front of it. The next time it is shown the kids proclaim "they got it working" and walk from behind the machine and start playing.
Continuity mistake: During the dance hall scene, the first half of the guitar solo Marty plays (before the Eddie Van Halen section) is completely different to the one he plays in the original film. Whether this is just to give time for the jump sequence to take place or not is open to question, but all the same, although not many people would notice, it is a pretty obvious mistake. (01:26:00)
Continuity mistake: At the start of this film (and the end of the prior film), Marty and Jennifer talk with Doc who has just returned from the future to retrieve them. A shot looks over the rear half of the DeLorean at Marty and Jenn and we see the street behind them. Ignoring that Jennifer is now played by a different actress, there is a tree missing behind her, as is the truck with a camper-shell that was two driveways back. Parked in the street is a VW bus where a Pontiac Firebird was. Marty has also gained a wristwatch not present in the same scene in the earlier film.
Continuity mistake: As the DeLorean lands in 2015 at the start, the car has silver center caps (between the wheel nuts) in the front and back wheels, but in the very next shot, they have changed back into the original black center caps. (00:06:00)
Continuity mistake: At the start when the DeLorean crashes into the line of six bins on the driveway one of the bins is half open. It is one from the right. In the next shot when Dr. Brown gets out the bin that is half open is two from the right. Then a bit later when the DeLorean comes out of the driveway all the bin lids are closed. The bin lids were never closed all through the scene.
Continuity mistake: After George knocks out Biff, Biff has an obvious contusion and blood on the right side of his nose and mouth. As the hoverboard chase scene progresses over the next several minutes (particularly in the lighted tunnel), the contusion and blood repeatedly disappear and reappear on Biff's face from one camera cut to the next.
Continuity mistake: At the end of BTTF 1, when Doc tells Marty and Jennifer that they have to come back with him to 2015, while they are sitting in the DeLorean, the Doc says," ...where we're going we don't need (pause) roads," and as he says "roads" he puts his silver glasses on normally. But in the beginning of BTTF 2 in the same scene, when he says," ...where we're going we don't need (pause) roads, he swings his glasses on really fast with only one swish as he says "roads."
Continuity mistake: When Marty is reading the letter from the Western Union man, he's standing with the letter in front of him at chest level. Switch to side camera angle and he is now bent over, holding the letter down to the car's headlight. Switch angle again and he's standing up again, with the letter back in front of him.
Continuity mistake: At the end of BTTF, when Doc drives up to Marty's driveway and tells Marty and Jennifer to get in the car to go to the future, Marty asks Doc, 'Why, what happens? Do we become a**holes or something?' Then Doc replies straight away 'No, you and Jennifer turn out fine, it's your kids, something's gotta be done about your kids.' At the start of BTTF2 when the same scene is played again, Marty asks the same question but this time Doc pauses before he replies to Marty's question. (00:02:00)
Continuity mistake: When Biff and Marty fighting over the almanac while driving towards the tunnel, the almanac flies out of their hands and lands on the front windshield. Biff slowly reaches over the windshield blocking the center rearview mirror entirely with his right shoulder. Cut camera angle and the mirror is unblocked, showing Marty to the rear of the car, then a reaction shot of Biff seeing Marty in the mirror, all while he is still blocking the mirror with his shoulder.