Patzer

When old Biff steals the time machine to change the past, he returns the Delorean back to 2015 so Doc and Marty would suspect nothing. He should instead have arrived in the alternate version of 2015 just like Marty and Doc went to the alternate 1985. No explanation is given as to why he can return to the unaltered time-line while Doc and Marty can only get to alternate versions of the time-line. In The Big Bang Theory (2007), the episode The Focus Attenuation (2014), they suggest that this could be because when Old Biff travels forward, Young Biff hasn't made his first bet that starts the time-line changing yet, thus allowing Old Biff to return to the original 2015. Possible explanation: It is implied that Lorraine eventually got totally fed up with her abusive married life, and shot Biff to death sometime within just a few years after the time when Marty saw them in Alternate 1985 (this is the real reason that Old Biff clutches his chest and crumples to the pavement as he is exiting the DeLorean after returning to 2015, not because his aging body couldn't tolerate the physical stresses of time-warping, as most audience-members would have assumed was happening), removing him and his toxically-greedy influence on the Hill Valley area. The logical "further" idea, therefore, is that the decent-hearted Lorraine --- along with 99% of the other locals, who of course would themselves have also strongly disliked the dystopian wasteland that their community had degenerated into --- would then have banded together en masse --- "in numbers, there is strength" --- and ousted whatever "scum of the earth" officials and politically-influential residents were currently present in the area, and then made sweeping changes for the better to get Hill Valley back to being the peaceful bedroom community that it had been before Biff's interference that had started in the late '50's. Also, Hilldale --- where the McFlys were now living --- was quite a distance from Hill Valley, and so it's possible that Biff's dissipative influence hadn't reached that somewhat-geographically-removed area so much as it had affected his own immediate stomping-grounds.

In all the scenes of Young Biff and Old Biff riding in the car together, the car has no rear view mirror on the windshield. When Young Biff first comes back out and gets into the car again ("I'm going to the dance, Grandma"), it still has no rear view mirror, yet after he backs out onto the street and it then cuts back to the shot looking in toward the windshield, a mirror is present.

When Marty retrieved the sports almanac from the garbage can in Strickland's office, it was the almanac cover wrapped around a girlie magazine. However later when Marty grabbed the almanac from the unconscious Biff, the almanac was intact with the original cover.

In the opening scene in which Doc arrives at Marty's house, the time on his wristwatch is actually different from what it was in the identical scene that closes off Zurück in die Zukunft (1985).

The cooling vents on the back of the DeLorean change between silver and black throughout the film. A clear example of this is the first landing scene of the DeLorean in the alley in 2015.

There is no way fifty years worth of horse races, MLB games, NBA games, NHL games, NFL games, (as well as every other game mentioned) would fit into a book the thickness of the almanac used in the film.

When Marty, Jennifer and the Doc first arrive in the future it's raining. Despite traveling at 88 mph or above, the rain on the passenger windows of the DeLorean runs vertically down. Air velocity at that speed would push rain back faster than gravity would pull it down.

All the sports scores young Biff hears on the radio in 1955 are correct except for one, Texas A&M @ Rice. In the movie the score is stated as "Texas A&M over Rice 20-10". The real score was Texas A&M 20, Rice 12.

The 50-year Almanac has only a few dozen pages, and so the sports stats for 1955 would be listed just a few pages in from the front cover, yet Old Biff opens the book to a random spot that's clearly much nearer the middle of the book.

When they travel in time and the airplane flies by, you would see flames if the plane had afterburners. Only military jets have them.

While in 2015, Doc explains the consequences of 1985 Jennifer coming face-to-face with her 2015 counterpart... either they pass out from shock or there is a "time paradox" that could destroy the galaxy. Yet, when Old Biff from 2015 sits down and has an entire conversation face-to-face with Young Biff from 1955 - neither of Doc's predictions come true and absolutely nothing happens. What is actually happening is that Young Biff is too stupid to realize he's talking to his older self, just a "crazy old codget with a cane". Even when Old Biff tells him he's a distant relative, Biff claims he doesn't see a resemblance.

"The newspaper that Doc Brown shows to Marty was USA Today, a national newspaper. A national newspaper would not print a local robbery as a front page article."

The upper right corner of the newspaper clearly indicates that the paper is the "Hill Valley Edition" and not a nation-wide publication.

Near the end of the movie after Marty burns the sports almanac, Doc looks at the newspaper from alternate 1985 which mentions him being committed. There is also an article that Nixon is seeking a fifth term. In 1985, Nixon would have already started his fifth term in January (after Nov 1984 election). Term 1 1968-72; term 2 1972-76; term 3 1976-80; term 4 1980-84; term 5 1984-88.

It is never specified that Richard Nixon was seeking a fifth consecutive term; if someone else served as president for a full term in those intervening years, then Nixon would be seeking a fifth term in the upcoming election.

Once it became apparent that Biff was unerringly choosing winners each time be placed a bet, the odds would fall to even money each time he wagered which would keep him from winning any money, unless he intentionally lost occasionally on purpose. It has been established that Biff was not very bright, so it probably not occur to him to do this.

Once Biff established his fortune early by winning bets based on the almanac, if the odds started to drop he could easily have used his minions to make proxy bets on his behalf in order to continue to amass his fortune.

Biff using the almanac to win at sporting events between 1955-1985 wouldn't have worked, since him winning would change history along with most or all of the statistics, dates, and games, rendering the book useless after the first few wins (at least).

When Marty sees George deck Biff, we see the Marty from Zurück in die Zukunft (1985) running out to the parking lot. When he glances at the photo and splits, the couple he runs in to are completely different to the actors in the first movie and they don't say anything to each other, whereas they should have been seen to say 'Who is that guy?' 'That's George McFly.' 'THAT'S George McFly?' as they did in the first movie before Marty bumps in to them. Furthermore, when Lorraine is picked up off the floor by George, we see his hair is shaved very close at the back and sides, but in the next shot the new actor playing George who leads Lorraine away doesn't have closely shaved hair.

When Marty is watching his other self talking to his parents, Biff's shadow can be seen on the wall. He is waiting for his cue.

When they first arrive in 2015, Doc says "Here's our exit" and turns the wheel to the left. Then in the next shot the car turns right.

At the beginning of the film, when Doc drives into Marty's driveway and knocks over the trash can, the driver (an obvious stuntman) is not wearing the futuristic sunglasses that Doc removes in the next shot.

When old Biff and young Biff are driving to young Biffs house the car gets scratched on the drivers side, yet when they drive into the garage young Biff is checking the scratch on the passenger side.

When old Biff returns to 2015 after giving 1955 Biff the Almanac, he should have returned to an alternate future where Biff was rich not the same 2015 he left earlier. This is explained to Marty by Doc later when Marty questions whether they can go to 2015 again to stop old Biff from getting the almanac. In The Big Bang Theory (2007), the episode The Focus Attenuation (2014), they suggest that this could be because when Old Biff travels forward, Young Biff hasn't made his first bet that starts the time-line changing yet, thus allowing Old Biff to return to the original 2015.

When arriving in 1955 at the Lyon Estates sign, the flux bands on the flying DeLorean are lit up blue on the flying model and remain on until we see the car landing behind the sign. They are only supposed to light up when hitting 88 miles per hour. They are never lit up after entering and exiting the wormhole.

When Marty was at the back row seat of the car and with Biff driving in front, Marty could talk to Doc through the walkie-talkie without lowering his voice, and Biff was completely unaware that Marty was there.

To Biff's surprise, Marty steps off the roof. Then lands on the Delorean. Somehow the rising door of the Delorean extends over the edge of the building and strikes Biff under the chin. Later, Doc lands the Delorean behind a billboard. A door opens and rises within the available space. It does not extend beyond the edge of the wall.

Just before Doc and the Delorean get struck by lightning, Doc says he'd have to "circle around and make a long approach from the south", due to the heavy crosswind. However, there was no reason Doc couldn't have landed the Delorean immediately after Biff's car had slid into the manure truck, as the weather was calm.

When Biff gets his car back after manure clean-up in 1955, the detailer's truck has a tail light from a GM van from the 80s.

As Marty is crawling across the electrics position above the stage at the enchantment under sea dance in 1955 you can see a few lighting fixtures hanging there in the background. You can see a Altman 360q Axial Ellipsoidal Reflector Spotlight which wasn't introduced until around 1971.

Marty, Doc Brown, and Jennifer arrived in the future on October 21st, 2015. According to the newspaper seen on their arrival on October 21st, the world series was already completed. The world series of 2015 had not started, yet. The 2015 World Series started October 27th and was finished November 1st.

When the first Marty (from Zurück in die Zukunft (1985)) is waving to George McFly while playing "Earth Angel", you can still hear the electric guitar, even though he isn't playing it.

At the beginning of the film, as the Doc departs the McFly house with Marty and Jennifer, the camera is briefly reflected in the rear futuristic shiny license plate.

When Marty jumps into the water and Griff and his gang fly into the courthouse, the crew (looks like a crane camera) is reflected in the door that Griff smashes through.

When Griff drops his pit bull board a blue stand is visible as he steps onto the board.

When Marty does the "switcheroo" in the hotel stairwell to avoid rich Biff's thugs, a crewmember's shadow is visible at the spot Marty jumps to. This can be seen right before the camera pans upwards to reveal Marty a few flights up running towards the roof.

When Marty and Doc talk about going back to 1955, whenever the camera is focused on Marty, you can see what looks like some sort of mechanical device or someone using the equipment outside of the window. This can be seen between 01:01:56 and 01:01:57 and also 01:02:03 and 01:02:06

When Doc comments on how great the weather service is, he looks up at the sun past the buildings, yet the side of the building facing Doc (away from the Sun) is lit by sunlight.

When old Biff gives the Almanac to his young self in 1955, he altered the future, creating a new timeline. So with this change, he could not go back to the original timeline, since it was altered. He should have traveled to the new 2015.

It has been mentioned that when Biff delivers the almanac to his younger self, he should not have been able to return to 2015 without arriving at a variant time-line. But this plot hole goes back even further than that, to the beginning of the film. In the version of 1985 where Doc picks up Marty and Jennifer, once they get in the car and disappear, they no longer exist in the time-line. When they arrive in 2015, it would be a version of 2015 where they got into the DeLorean in 1985 and were not seen again until arriving in the future. However, this could simply be because they are intending to and fated to return to continue their lives.

When Marty and Jennifer travel with Doc to the year 2015, they both find older versions of themselves living in that year. This shouldn't have happened considering that Doc's dog, Einstein, traveled one minute into the future in the first movie, and there was no one-minute-older-than-himself version of him then, in addition to his original self. However, this could be explained because Doc Brown didn't and never intended to send Einstein back to live through that minute, while Marty & Jennifer are intending to and are fated to eventually return to 1985 to live out their lives.

Doc shows is BTTF2 the time line. He says that the time line has been altered and that "the time line skewed into this tangent, creating an alternate 1985, alternate to you, me and Einstein, but reality to everyone else".

If time travel were possible, a person who went back in time would not change the future for the people they left behind. Those people would continue forward with their time line. Doc, Marty and Einstein would jump to alternate time line.

The other problem is that the Doc that Marty goes back to wouldn't be the same one that he once knew. The same with the old Biff going back to give the Sports Almanac. The old Biff would never see any of those riches. He would continue his path unaltered.

At the beginning of the film, it makes no sense for Marty and Jennifer to go to the future. Think about it, Emmett "Doc" Brown only has to tell them about their future problems.

As Doc and Marty are about to travel back to 1955, Marty says, "What about Jennifer? What about Einstein? We can't just leave them here." When he says this, the shadow of the boom operator and boom microphone can briefly be seen above him and on his t-shirt.

In the beginning, in 1985, Doc assures Marty, "you and Jennifer turn out fine". They were far from fine. Marty lost his career as a musician because of the incident with the Rolls Royce, hated his job which he got fired from, Jennifer was disappointed that they got married in the Chapel Of Love. They were clearly miserable. However, it's quite likely Doc Brown was hiding this information from Marty to avoid Marty feeling compelled to fix his life, a tactic which is in line with the Doc's drive to not alter the past (and having spent time in 2015 he may include 1985 as part of "the past").

Doc doesn't interfere with the police officers picking up Jennifer, saying that the officer wouldn't believe that he and Marty were time travelers. However, these same officers accepted without question that Jennifer was her older self, despite her youthful appearance, because of her thumbprint. Marty's thumbprint also would not have changed, so he could easily prove to the officers that he is his older self, Jennifer's husband.

Doc tells Marty that they cannot stop the police from picking up Jennifer, because if they say they are time travelers they would be picked up as well. However, Marty had just successfully impersonated his future son, and the police already believe that Jennifer is her 47 year old self, despite her youthful looks. Marty could pass himself off as either himself or his teenage son.

In the first movie, Doc mentions that when he travels 25 years into the future, he'll be able to find out who wins the next 25 World Series. This implies that he would use that information to bet on the games when he returned to 1985 on.

But in this movie, he scolds Marty for getting the Sports Almanac and planning to do the same thing. However, it could instead simply be that he realizes he won't live long enough to see them while living normally, so he's "flipping ahead in the book" to see how baseball will progress. Another possibility is that he clearly has spent considerable time using the time machine off screen before the beginning of this movie, before picking up Marty & Jennifer, it may be that he himself did some time traveling money making in order to fund his 2015 activities, where he faced difficulties that led him to this viewpoint that it's a bad idea.

When Marty leans over the unconscious Biff and grabs the Sports Almanac, while getting up he ends up holding it an inch away from the other guy's face (Wesley Mann, who doesn't know what Marty means by "CPR") before running off, and "CPR Kid" from then on declares several times that he thinks Marty stole Biff's wallet. The magazine was inches from his face, there's no way he could mistake a magazine for a wallet from that distance.