There is probably a good reason why we're never introduced to any of Biff's kids in the BTTF films. Biff most likely had kids, but he went through a divorce with his wife. She got custody over them and probably moved away to another town or even another state. After all, this is Biff we're talking about and what woman would want to permanently be married to him? That's why Biff is still able to have a grandson.
The Contrived Coincidence of Old Biff choosing the day of the Enchantment Under The Sea dance to give himself the almanac isn't actually one. Think of it from Biff's perspective: the day that George knocked him out and won Lorraine's heart, and also became his greatest enemy, certainly would've been the worst day of his life. What better day to give himself the almanac? (It's also the day of the Hill Valley Lightning Storm, an important day in local lore that Old Biff would probably remember the exact day of offhand to punch into the time circuits.)
November 12, 1955 also had that amazing upset and sudden reversal by UCLA, providing a perfect example to the dim-witted Young Biff that the Almanac is for real.
A deleted scene adds a further reason, since the mechanic Terry, when trying to get Marty to donate to the clocktower fund, mentions that the day of the lightning strike was the day that Biff tried to con him out of the $300 for repairing his car and he and Biff have a brief argument about it. Because of that, the memory of the date would have been fresh on his mind when he discovered the time machine a few minutes later.
Marty, Doc, and Biff's time traveling and changes to the spacetime continuum is the reason the real 2015 looks nothing like the 2015 shown in the movie.
As Minty Comedic Acts points out, it's fitting that the second movie is about deconstructing building a happy ending around material happiness, which is something that some audiences criticized the first movie for implying. For one, we have future Marty. While Hilldale is indicated to now be a rough neighborhood, he still lives in a (relatively) decent home, surrounded by the amazing wonders of the future, to which present Marty is awed. But it doesn't mean anything to future Marty, given he's miserable from having lost his rock star future, thanks to the worst mistake of his life.
Marty's bad future with Biff. Even when compared to the 1985 George who's a successful author, Alternate Biff is probably 100 times richer, has 10 fold as much material riches, and lives in a penthouse. But are Marty and Lorraine happy? Heck no! Lorraine has to live with Biff's swift hand and bad mouthing about her first husband (and the plastic surgery he coerced her to get). Luckily Marty didn't have to live there for long.
If Biff blackmailing Lorraine that he'll send her children to jail for debt is any indication, it's because of material desires that got the former-McFly family deep in Biff's pocket.
What set off the domino effect of Old Biff creating the Alternate 1985? Marty buying the future almanac in pursuit of getting even more rich than he already was, inadvertently sacrificing his already wonderful life and family for simple greed. From this mistake, Marty learns it's his family he values more than being rich.
Marty having an issue over being called chicken doesn’t come out of nowhere. Considering how much of a coward his father was, Marty probably hated the idea of being compared to him, thus the whole chicken thing. Also, in the first movie, he didn't really do anything that warranted anyone calling him chicken, thus why it never came up.
The novelization for the first film (which used an earlier screenplay draft as a guide) has a couple scenes where Marty and George have conversations about being called a chicken. So, it's possible the script for the first film had some of that "Nobody calls me Chicken" thing, but it was cut out.
Why did Biff never get suspicious about the flying DeLorean he saw in 1985? Because at some point after that, flying cars become widespread, so he must have assumed it was a prototype.
Also, the car accident that messed up Marty's life happens as a direct consequence of him fixing his family in the first movie, because in the unchanged timeline Biff wrecked the car, so Marty couldn't have drag raced anyone. The sudden appearance of Marty's chicken problem may also be directly linked to him now trying to live up to the high standard set by his overachiever father, instead of struggling with the poor self-confidence learned from his unaltered father.
The end seems to be a bit of silly movie magic that the mailman arrives exactly on time, doesn't it? But this is a letter that they'd been holding for nearly three quarters of a century, a package that would have been increasingly the topic of conversation as the time drew nearer. They had a betting pool going as to whether or not this "Marty McFly" was even going to be there. They likely had some debate over who would actually deliver it. If you had the opportunity to confirm or debunk a seventy old urban legend (even if it's only an urban legend around the office), wouldn't you take an almost extreme amount of precautions to ensure that you got there when you were supposed to?
In the same scene, why does it take so long for Biff to follow Marty when his Mooks come out of the elevator? His gun holds 5 bullets, all of which he uses before Marty exits the lounge. He had to go back for more bullets.
One might wonder how the Sports Almanac would always have the correct sports results. After all, the worldwide proclamations of Biff's luck may affect the games in some way, such as which players join which teams, how players feel during the game, etc. Well, since the Almanac comes from the future, any changes to sporting results would be reflected in the Almanac by way of the Ripple Effect! 100% accuracy guaranteed!
Until Biff pushes the timeline so far that "Grey's Sports Almanac" is never published, instead he winds up with "Biff's Greatest Sports Bets."
Furthermore, Biff did not continuously use the almanac for everything until 1985; he made his vast fortune with it in the years after 1955, then invested it all in his various industries. He likely hadn't needed to use the almanac for betting money in many years, hence why it was locked away in his office safe.
Doc was willing to use time travel to save 2015 Marty's family, but why wasn't he ever willing to keep Marty from ruining his life in the first place by doing something about the accident with the Rolls-Royce? The answer is he actually was, but in an indirect and roundabout way. By having Marty disguise as his son and turn down Griff Tannen's job, it would have hopefully made Marty grow out of the Fatal Flaw which caused the accident in the first place. Doc understands that using the time machine to fix things is wrong and that improving oneself is better all around, so he instead opted to do something that would help Marty grow up instead.
Doc actually explains, in the third film, why telling Marty straight out about the accident would be foolish: in the scene where he blurts out "That's exactly what causes you to get into that accident in the future," Marty asks him what he's talking about, and Doc replies that telling him "might make things worse." Doc realizes that if he tells him about the accident, Marty might manage to avoid that particular catastrophe, but then with the future thrown into flux something even worse might occur as a result of Marty's recklessness. He might even end up dead. The only way to prevent not only the accident but any other disaster resulting from this trait of Marty's is to teach Marty to outgrow the trait—and that's part of what Doc is trying to do, subtly, throughout the second and third film.
2015 looks a lot more advanced than our 2015. Why would that be? Doc Brown disappeared in 1985, but before he did so he could have published details to one bit of his project he could talk about - a car-sized nuclear reactor capable of producing power equivalent to a civil fission reactor (if only for short periods). This led on to the development of Mr. Fusion, and advanced technology by decades.
If you look at the tombstone of George McFly in Bad 1985 and do a little math, Marty would have been just five-years-old at the time of his death. As such, you can understand why Lorraine was confused about Marty asking about George and why Biff was skeptical when Marty claims that George told him about the manure incident as an explanation for how he knows about it, since it seems unlikely that he would remember something from that age.
Now a bit of both Fridge Heartwarming and Horror: Marty told Biff he learned about the manure incident from his father to protect his mother, the only other person Marty knows that could have known about it. If Marty said it was Lorraine who told him about the incident, Biff most likely would have reprimanded her in retalation, but since George was already dead, there's nothing he could have done about it.
Why are Griff's cronies wearing makeup on their faces? It turns out that style of makeup disrupts facial traits and prevents facial recognition software from recognizing the wearer.
Also, when Marty pulls a Groin Attack on Griff, we hear a metallic noise. We've already seen that Spike (the one female gang member) has a propensity for using the claws she's attached to her fingernails for such purposes. Hanging out with her, seems that a protective cup is just common sense for any guy.
Based on what we know from the sequels, Doc's reassurance to Marty at the end of the first film that "you and Jennifer turn out fine" isn't quite accurate. Of course, the filmmakers have explained in interviews that they had no plans for sequels when they made the first film, and that they intended this scene merely as an amusing throwaway. So apparently they ended up developing the story of Marty and Jennifer's future a little differently than the first film suggested. But compare the way Doc delivers that line in the first film with the way he delivers it in the reenactment of that scene in the second film. The difference is subtle, but real. In the first film, he speaks the line matter-of-factly, and he has a sincere expression on his face. In the second film, after hearing Marty's query "Do we become assholes or something?", he pauses, his eyes turn to the back of his head for the briefest of moments, then he sputters, "Oh no no no no, you and Jennifer turn out fine." Unlike in the first film, it looks like he's hiding something. Considering that we later find out the pivotal accident which ruins Marty's musical aspirations is set to occur the very next day, and Doc knows it, that shouldn't be surprising.
It is possible that these are two different versions of Doc Brown. As speculated elsewhere, the actress change for Jennifer might have significance in-universe.
In an extended scene from 2015, we see Old Biff fading out of existence for some reason. It was omitted for being a little pointless in retrospect, but Word Of God states that at some point, Biff was shot by Lorraine with his own gun. Why did Old Biff still manage to travel to the past to drop off the almanac before fading away? It's possible that this was such a huge change to the timeline that it would take a long time for the ripple effect to really catch up with all the details. It's not just changing a few people's lives, like Marty did in the first film, it's changing an entire town filled with people, and possibly the face of the entire world when you consider the economic damage from Biff winning so much money, undoubtedly spending it all, and even the implied political influence he has with Richard Nixon. TL;DR, Marty and Doc were on a time-limit ever since Old Biff came back to 2015, and they didn't even know it. If they had spent any longer chasing after Biff, there may have been a major paradox simply by default. After all, we can't expect Biff to understand anything more complicated than a jigsaw, never mind the space-time continuum.
At first, Biff's grandmother is simply a grouchy character for the sake of a grouchy character. However, once you play the Telltale game and learn who Biff's father was, you begin to realize that maybe she didn't have much reason to like Biff at all: her son was a bootlegger under a life sentence and Biff is turning out like him. Or, she could be projecting her distate for her son onto Biff as the IDW comic showed they had both had a less than amicable relationship with her, which could explain why he turned out the way he did.
Biff's choice of movie, A Fistful of Dollars is rather fitting. In the movie, the villain stole the wife of another man, and who comes to the rescue? Clint Eastwood of course, which is also the alias that Marty uses in Part 3 when he is in the old west. And of course Marty rescues his mom from Biff by restoring the timeline.
When Marty finally gets the sports almanac back from Biff after Biff gets punched out, a bystander (sometimes referred to as "Wallet Guy") humorously says, "I think he took his wallet." He's not technically wrong - by getting the almanac back from Biff, Marty has effectively taken all of Biff-A's future winnings, the equivalent of "taking his wallet" multiplied by thousands.
Biff ending up in auto-repair in part one was an indication of how much he had fallen from the original timeline. But in this movie, we see why Biff would go into the business: having a massive bill for his repair would make him see auto repair is a pretty lucrative business. Without George to do his homework for him, Biff would see it as a good fallback if he couldn't get into college.
The question may be raised as to how could Old Marty, Old Jennifer and their kids exist in 2015 if their younger selves left the timeline in 1985. Remember in Part I, when Einstein traveled forward one minute, he didn't exist for that one minute. Based on that logic, Marty and Jennifer would cease to exist from the moment they left 1985 and there would be no one to grow old, get married and have kids. That would be worthy of a Headscratcher entry...until you remember the Delayed Ripple Effect. When Marty changed history in Part I and prevented his parents from meeting and falling in love, he had less than six days until he started to fade away from existence. Using that as a reference, Doc, Marty and Jennifer would have less than six days to exist in 2015 until it changes into a timeline where Marty and Jennifer disappeared in 1985.
1985-A Biff's mistreatment of Marty makes sense in a few ways.
Considering how viciously Biff attacks Lorraine when she claims he'll never be the man George was, Biff still is nursing a nasty grudge against the first person to ever make him feel small. Smacking Marty around is Biff's twisted posthumous revenge against the "loser" who dared stand up to him.
Biff may be an idiot, but he might notice Marty looks like "Calvin Klein", the other "loser" who (in his mind) caused him 300 dollars worth of damages. Biff might hate Marty for his "resemblance" to that "other loser."
In a more tender example, Doc knew Marty would go to the cemetery once he found out about George's murder. How did he know this? Since Marty is Doc's closest confidant, Doc would know about Marty and his family life, including how much he cares about his father. Aww...
Biff bullied George into doing his homework and this dynamic carried into adulthood, with Original 1985 Biff bullying George into writing his reports. Original Biff goes so far as drive drunk with George's car, totaling it. Biff only gets away with his idiotic behavior because George and others are too scared to stand up to him, meaning he can continue to act like a teenage moron.
However, because of Marty's actions, George stood up to Biff. Suddenly, Biff had no one to do his work for him, everyone stopped being afraid of him, and he was likely outcasted for trying to force himself on Lorraine. Having become a complete social pariah, Biff was forced to clean up his act because he had no one to bail him out and learn some kind of trade to support himself. His anger at his younger self is because his stupid decisions made his life harder in the long run.
Despite the classist notions of blue-collar work, it does take a degree of intelligence and skill to run your own auto-repair business. The altered Biff did gain some work ethic.
If Old Biff can laugh at the manure incident, it implies Biff did become a kinder person. I mean, why else would George and Lorraine hire their former abuser and predator, respectively, to do maintenance on their car? You really would have to turn your life around if your former victim lets you near your family.
This is why 1985-A Biff is such a tyrannical manbaby. Because having functionally won a lottery by getting the sports almanac, he didn't have to work or better himself.
If Altered 1985 Biff was a better person, why did Old Biff become a grouch who would travel back in time to make himself rich? The fact that he's bullied by his own grandson implies Altered Biff's family life wasn't exactly pleasant. Old Biff doesn't seem to have any friends or even a wife either, clearly still pining for Lorraine in 2015. Whether this was his own fault or whether his own family hurt him, it is easy to see why Old Biff lost some of the happiness his altered middle-aged self seemed to have.
Griff having a female member of his gang is a subtle sign of the greater acceptance of women in society, albeit in a twisted way.
In 1955 and 1985-A, Biff's gang is all male. In the 1950s, women weren't seen as violent or capable in a fight, and teenage Biff would find a girl being a good addition to his gang as ludicrous. 1985-A Biff, based on his abuse of Lorraine and affairs, would have an even lower view of women.
Since the 1950s and especially in modern times, women in action roles, heroic or villainous, have become far more common. So while Griff is still a bad guy, he might not have a sexist belief that women are inherently weaker.
Turning Hill Valley into a place worse than Hell isn't being done just for kicks by Biff. One of the things that the bat-wielding father yells at a retreating Marty is that he won't be intimidated into selling his home. It's implied Biff owns the realty company that wants to own the man's home. So Biff wants to buy land and like any good businessman he wants to buy land cheap. Unleashing a crime spree in his town is a good way to buy land as cheaply as he wants by lowering the property values. It really shows how vicious Biff is that he would ruin his own hometown for a quick buck.
Doc getting sent to a mental asylum makes sense:
Historically, insane asylums were often used by governments to lock up political opponents on the basis of "bringing them to care." If America has become more authoritarian, then this might be one of their tactics to clamp down on dissent, as Doc is the kind of person who would protest a corrupt United States.
Old Biff warned Young Biff about a doctor who could potentially get in his way. Young Biff figured out Doc could build something that would defeat him and had him institutionalized to stop him.
Doc didn't exactly have a good reputation, and so a lot of people would readily treat him as a maniac to be imprisoned.
The fact that the future turned out so differently from what he learned from Marty in 1955 might have caused Doc great anguish over what went wrong, which might have made him look more unstable in the eyes of others.
Biff-A not expecting Marty to be "the kid" the "codger" warned him about. Since he didn't recognize the codger as his future self, he likely expected the kid to be somebody who was a kid back in 1955 instead of somebody who wasn't even born back then.
This does once again bring up the Fridge Logic of no one recognising Marty as Calvin Klein though.
It's likely that, by the time Marty started looking like his 1985 self, people who met "Calvin" already forgot what he looked like.
Marty recognizing the NES/arcade game Wild Gunman could be a case of Artistic License – History as the game itself wouldn't see a nationwide release in the USA until well into 1986. But there is another way Marty recognized the game and had become so good at it. He knew someone who had an import version of the game from Japan or who had acquired the game on a visit to New York City; as of October 1985, the NES and its launch games (including Wild Gunman) were only released in New York City as a test market.
The "lithium mode on" scene. Marty activates it and blames his kids for turning it off. From this article on The Other Wiki, we can infer that "lithium mode" consisted in dissolving lithium salts into the household water supply, which Marty used to treat himself. His kids did not need it, but they were forced to drink lithiated water anyway, which affected their brain chemistry and turned their behavior into what we see in the movie. They deactivated lithium mode because they wanted to snap out of it and be normal, but their father won't let them because he only thinks about his own needs.
After Marty and Doc have returned to their drastically altered future, where Hill Valley is overrun with crime, Marty places Jennifer on the porch of her house. Before leaving, he comments that there are bars on her windows, something that probably wasn't there before. We later find out that Marty's house is no longer owned by his family. So why would Jennifer's house still be owned by her family in this timeline? For all we know, Marty just put her on the front porch of a house full of serial killers and date rapists. Who knows what happened to her in between the time they dropped her off and came back.
Marty has kind of an "oh shit" moment regarding this in the movie. Whatever happened, she was still on the porch and asleep and unharmed by the time Marty came to pick her up. Considering that only a few minutes had passed for her, and that the timeline had caught up with her across the transition from Hell Valley '85 back to its proper state, nothing happened because whatever horrifying things would have happened to her were averted before they could actually transpire. What would have happened, if "Hell Valley" had gone along unchecked, is probably better left to terrifying fan fiction.
There is all kinds of horror when you think about why Lorraine ended up stuck with Biff.
Lorraine is cowed into being with Biff with threats of her kids being cut off. This is a very real threat for someone trapped in an abusive relationship, but it gets even worse when you consider how utterly impoverished and desolate 1985-A is. Real Life America is already a place where a single mother of three can find it difficult to support herself and her kids, but the utter desolation of 1985-A makes this reality harsher. Lorraine has literally no other options to support her children. It also shows while Lorraine might not care about getting cut off from Biff, she is frightened about her own kids getting cut off: because this broken America is a harder place to make a living.
You have to keep in mind that Biff owns all the businesses and could probably tell the hiring managers not to give Lorraine or the adult children jobs, or even tell colleges not to accept them, so they have no career options and are stuck with him. It's also implied that Biff holds a lot of power on both the state and national level. Even if Lorraine and her children could get away to another state, Biff would track them down and exact revenge against them.
1985-A Biff boasts about how the police couldn't identify the gun that he used to kill George. But in several points, he outright boasts about how he "owns the police" and he can have the McFly's thrown into jail. In Real Life, wealthy and powerful men like Biff do get away with a lot of things, but in 1985-A, America's political systems have likely decayed so much, men like Biff can outright buy the legal system and not merely manipulate it. Lorraine can't simply call the cops on Biff, divorce him, or even surreptitiously record his abusive statements: Biff can sic the law on her and her family as there's nothing she can do about it.
American jails are already lousy places to be: bad food, sometimes abusive authorities, and sexual assault. But if 1985-A America has decayed so severely, that prisons must be Hell on Earth. The far more functional 2015, as seen by Doc and Marty, still had kangaroo courts where you can't have legal representation. So imagine how corrupt and dysfunctional the judicial and prison system is, and you can see why Lorraine would stick with Biff to keep her kids out.
Lorraine has likely deduced Biff killed George. But as stated above, even if she had evidence, Biff has too much power and connections to be brought down legally. Considering how cruelly Biff treats Marty, Lorraine is terrified that Biff could kill Marty or even hire someone to do it for him.
In the original timeline, Lorraine wasn't in picture-perfect health, largely because her marriage to George was pretty unfulfilling. But in 1985-A, she's had to endure physical and emotional abuse from an evil husband, grief from George's murder, stress about her children's financial situation who also have to go through Biff's abuse, her hometown becoming a Wretched Hive and is drinking a lot more to cope with it all. It is safe to say her health is far worse. This could also explain why Biff forced her to get plastic surgery: her marital situation has ruined her physical health, but Biff being Biff, would rather force his wife to look more appealing than actually shape up and give her and her children a more loving environment. It just shows how sick in the head Biff is, that he would abuse a woman, and force her to go through physical changes rather than actually help her.
When you see how horrific of a place the alternate Hill Valley (and its implied, the rest of America) is, it is understandable why that father tried to furiously beat Marty with a bat:
Hill Valley is so bad, even the straight-laced Strickland has been reduced to a gun-toting survivalist who has to worry about his mail getting stolen. One can imagine the kind of criminals that the father (and his children) is surrounded by.
The Papa Wolf screams at Marty that he's not gonna be terrorized into selling his home. This implies his family has been harassed by other people who covet his home. Since Biff in this timeline has remained a truly monstrous Jerkass without no love for anyone, it is possible he's the one who has been harassing that poor family.
In the Hell Valley setting, Strickland tells Marty that the high school was burned to the ground. Considering Biff in this timeline killed the guy who stood up to him in high school, it is possible he also burned down the school to get back at Strickland for being one of the few people who tried to discipline him. It reflects how Biff remained an abusive bully into adulthood, with the wealth and power to step on anybody he wants to. Biff would hate anybody who could get in the way of his "fun", like the school disciplinarian. And it is unlikely he would care about the kids who could've died in the fire to boot.
Strickland turning into a gun-toting maniac who would shoot someone for stealing his mail makes a ton of frightening sense when you think about:
In 1985-A, he faces the threat of a drive-by-shooting and the police is inadequate at best, it stands to reason why he'd be so paranoid.
Strickland had to see his school go up in flames and possibly his students die in the fire. While Strickland wasn't a nice man, he would likely be traumatized if some of his students were burned alive. If it was arson, it explains why he is so murderous to slackers like Marty.
2015 has no lawyers. Yes, it's a funny joke about the legal system, but think about it. Marty's son got fifteen years for being caught breaking and entering. Suddenly 2015 looks a lot less like a fantastic wonderland when you realize you can get arrested for practically anything and worst of all, even if you are innocent, you apparently have NO chance of being either defended or acquitted or even having your sentence reduced.
It gets a bit worse than that: the 6th amendment to the Constitution states that defendants have a right to legal counsel and the Supreme Court case Gideon V. Wainright ruled that defendants are mandated to have a public defender if they cannot afford a lawyer. Presumably this amendment would have been repealed and this ruling overturned in order to make the abolishment of lawyers possible. What kind of government exists that would torch an important civil liberty? And have any other civil rights been rolled back?
Why is it that when Marty kicks Griff in the groin there is an audible sound of steel? Is it perhaps because his friend/associate Spike likes to grab men by the testicles with her clawed hands and he knows exactly what will happen if he ever gets on the wrong side of her?
Old Biff may not realize it but by changing his own past, he's jeopardizing the existence of his grandson Griff. Indeed, the fact that 1985-A Biff marries Lorraine and there's no mention of him having any biological children strongly suggests that Griff would not exist in a hypothetical 2015-A. Of course, Griff is physically and verbally abusive towards Biff so maybe wiping him from existence was part of the plan all along, or it's simply that Old Biff is still so fundamentally stupid that he didn't realise that was a possibility.
Word of God says that Lorraine shot Biff in 1996-A. Does she get caught? Does she get sent to jail, or worse given the death penalty? Does anyone ever found out Biff's true character, or by that point no one cared? Did Biff know that Lorraine would get him one day, so he set everything up to make her life more miserable afterwards as a final "screw you"?
In addition to the curbs having neon lighting (so people won't trip on them or bump into them, presumably), houses have a neon strip above the garage door. As cars fly in 2015, it's probably so the homeowner can fly into the garage at night without risking crashing into the roof. Which also means there were probably numerous "crashing while trying to park" accidents before such a feature became standard issue.
The comics reveal that the Doc of 1985-A, whom we were told was sent to a mental institution, was also lobotomized. That's bad enough in itself, but the Marty of that timeline was shipped off to boarding school by his new stepdad. Does he know? Does he not know? Will he ever find out? There are only horrifying options.
If that's any reassurance, the Marty of that timeline probably never met Doc to begin with.
Being manipulated into getting plastic surgery is sadly a very common form of domestic abuse in real life and in its extreme form can lead the woman (and sometimes man) to develop severe body dysmorphia whenever they look in the mirror. Victims literally begin to resent their own bodies. Given how Lorraine has begun to refer to her own breasts as "these things" it would seem as if this applies to her. Between this and the attempted rape back when they were teens, it really does speak to how evil Biff is. He doesn't just want to be with her; he wants to own her both mentally and physically.
Child viewers often see Lorraine's decision to marry Biff as one of a Gold Digger who then ended up as a Broken Bird, whereas adults see a struggling single mom doing the best to feed her three kids (assuming she wasn't outright forced into marrying him). It's possible that the kids thought the same and ended up resenting Lorraine for giving them an abusive stepfather. One of them possibly even continued the cycle of abuse under Biff's influence.
A deleted scene reveals that Marty's older brother Dave became a drunken bum, likely to drown out his sorrow over resenting his mom in addition to everything else. Likewise, Word of God says that Marty's sister Linda would have become a hooker if her actress was available, so she may have become a hooker solely to spite Lorraine.
Biff-A attempting to murder Marty once he realizes he's "the kid" his older self warned about is already bad enough. But at least Biff-A had no idea Marty, Lorraine's son, would be the kid in question. Old Biff knew, and he still set up Marty to die. It is a clear sign that Biff never really reformed in the new timeline, and his "good guy persona" at the end of part one is just a facade.
Crosses over with Fridge Brilliance: Lorraine-A found out about Biff's attempted murder of her son, and that was the last straw.
The Hill Valley of 2015 is a relatively prosperous town with cool tech for even the poorest schmucks. Its only downside is the apparent repeal of the Sixth Amendment and the revoking of Gideon V. Wainrightnote The Supreme Court ruling that mandated defendants receive a public defender. In 1985-A, that sort-of optimistic future has been torched by Biff with many horrific repercussions.
Considering how many dangerous felons ran amok in 1985-A, imagine the crimes they could commit with access to the technology of 2015. Griff in 2015 was plenty dangerous with his bionic implants.
The relatively optimistic future of 2015 still featured debased civil liberties. So how much worse are things in 1985-A?
If the government has become more oppressive with time, then it will use that tech toward the policing and control of society.
Given that the newspaper of the alternate Doc being committed reveals that the Vietnam War was still going on as of 1983 in that timeline, that means that with his time travel, Biff (and by extension Marty for inadvertently giving him the idea and Doc for inventing the Time Machine in the first place), is indirectly responsible for thousands if not millions of deaths resulting from the prolonged war.
Based on what Needles says to Marty Senior about the McFly family's financial problems, did Junior get involved with Griff's robbery scheme because he wanted to help his family out financially? It's not implausible given how Junior tells Griff that he wants to talk it over with his father first.
points out, it's fitting that the second movie is about deconstructing building a happy ending around material happiness, which is something that some audiences criticized the first movie for implying. For one, we have future Marty. While Hilldale is indicated to now be a rough neighborhood, he still lives in a (relatively) decent home, surrounded by the amazing wonders of the future, to which present Marty is awed. But it doesn't mean anything to future Marty, given he's miserable from having lost his rock star future, thanks to the worst mistake of his life.