The 30 for 30: Fantastic Lies film adopts this trope for the infamous Duke Lacross Rape case. It first paints the picture of life and culture at Duke up to the accusation, switching to the accusation as one would expect when it comes up. Then, when it's revealed the accusation is false, there's a notable shift to the victim, Nifong, and just how things got this far when there was evidence from the very start that would have cleared the accused.
An American Terror starts out looking like it will be an Elephant or Zero Day-esque drama that follows a trio of social outcasts as they prepare to commit a school shooting, but then it turns into a Slasher Movie when the man who two of the would-be school shooters try to steal guns from is revealed to be a homicidal maniac complete with Torture Cellar.
Another Russian Movie, "The Arrows of Robin Hood" ("Стрелы Робин Гуда") has the heroes spent the first half helping an impoverished knight reunite with his Love Interest. They succeed, and the two get married, only to be fatally shot immediately afterwards. They are then never mentioned again, and the rest of the movie is devoted to Robin rescuing Maid Marian from the Sheriff.
Art School Confidential is based on a graphic novel by Dan Clowes, composed of one-page descriptions of art students. The film starts off as a riff on the comedic eccentricities of art and design schools... oh wait... there's a murder mystery? Yeah, also slip in an action sequence!
The first half-hour of Assault on Death Mountain (the sequel to Assault on Devil's Island) involves the main heroes trying to rescue a little girl from her evil millionaire father, and the final hour of the movie is about the heroes trying to stop an evil Syrian weapons dealer from unleashing killer gas on America.
Baz Luhrmann's Australia hits this midway through the film. Once Lady Ashley and the Drover deliver the cows to the dock, there's a Time Skip, and it's suddenly revealed that the main villain has been fed to crocodiles by his second-in-command, the narrative has jumped forward several years, and Australia is suddenly in the midst of World War II. During all this, the plot changes from "deliver the MacGuffin" to "rescue the child protagonist and save the Aboriginal children in the midst of Japanese bombing runs".
Avengers: Endgame: The movie starts with the surviving heroes from the last film planning to find Thanos, take the Infinity Stones back and use them to bring back everyone who died. They find him in the first 10 minutes, where it's revealed Thanos anticipated this and destroyed the Stones, and is now essentially a heavily injured retired man who poses no threat. He's quickly killed and the plot shifts to Earth's surviving population learning to cope in the post-snap world for five years, before Ant-Man returns and introduces another plot-switch: he accidentally discovered time travel, which will allow the Avengers to recover the Infinity Stones from the past.
BAPS begins as a screwball comedy about two girls from the ghetto who are hired to scam a dying millionaire into thinking one of them is the granddaughter of his first love. Halfway through the movie, their conscience gets the better of them and the movie takes a sharp turn for the dramatic as they get him to have fun in his last days while re-evaluating their own lives and relationships.
Better Watch Out starts out as a seemingly run-of-the-mill home invasion horror movie, as a babysitter and the adolescent boy she's watching over are stalked by an armed intruder. Thirty minutes in, we learn that the entire thing was set up by the kid and his friend, so that he could impress her by stopping the intruder and "saving the day". Unfortunately for the babysitter, the boy proves to be far more dangerous than a real burglar would've been.
In Ben & Arthur, the first half features the titular homosexual characters trying to have the state of California legally recognize their marriage; the second half focuses on the two dodging the sinister machinations of Arthur's religious brother Victor.
Birdemic is about a guy who gets rich off of green technology courting a girl whose modeling career is taking hold, only for birds to suddenly start attacking at the halfway mark. It's meant to be a modernized tribute to The Birds.
Black Bear: The film starts off with Allison, a former actress and indie film director, staying at a remote mountain B&B run by Gabe and Blair, who are having marriage difficulties. In the second half, everything is different. The trio is now part of a crew making a film (also called Black Bear) with a plot that resembles the first half. Gabe is now the director, and another actor plays his role in the film within the film. Allison and Blaire are now actresses, but their roles in the fictional film have been reversed, and Allison is also now married to Gabe.
Blind Date starts with the first half being about a man trying to survive a horrible blind date. In the second half, he's avenging himself and trying to ruin her wedding.
The Ed Wood-penned The Bride And The Beast initially starts off as the story about a newlywed who realizes that she is the reincarnation of a gorilla, which is the reason why male gorillas are aroused by her. Then halfway in, she and her new husband, a big game hunter, go on an African honeymoon and the film then turns into a story about the husband going after some escaped Bengal tigers attacking people on his campground. Meanwhile, the titular bride is shoved into the background, and no gorillas are seen until the last 10 minutes when the original plot finally resumes.
The South Korean film Phone starts as a thriller about a journalist who uncovered a pedophilia scandal being stalked by one of the people she accused. She moves into a friend's empty house and changes her phone number. Then her friend's daughter answers her phone and becomes possessed, and the plot suddenly becomes a supernatural horror movie about how the phone number is cursed by an angry spirit. Said spirit actually kills off the stalker halfway through the movie to put that plot thread permanently to rest.
The Cottage, a British movie, begins as a black comedy about a bungled kidnapping before turning into a dark horror comedy about a Leatherface-type slasher killer half way through. Presumably it was inspired by From Dusk Til Dawn.
The Dark Secret of Hendrik Schon: the documentary is about scientist Hendrik Schon, a titan in the field of theoretical physics. The first two-thirds of the program focus on his early career and work in nanotechnology. It builds up some drama around the unnerving applications — a weapon of assassination, an engineered biowarfare agent, the feared Grey Goo scenario, and so forth. Then around the 40-minute mark, a student reading one of Schon's papers picks up a clue that leads to his real "dark secret": He was a fraud. His papers were lies built upon fake experiments he never conducted and "evidence" he made up out of whole cloth. Whether this is a masterful subversion of the Science Is Bad hysteria, a piss-take on the idea that the scientific community knows everything, a Stealth Parody of sensational documentaries, or just a flaw in one such documentary is up to the viewer.
Another documentary that manages it is Hitman Hart: Wrestling With Shadows. It starts as a straightforward year-in-the-life documentary of one of the most popular wrestlers of the era. Then comes the Montreal Screwjob, and all of a sudden it's about one of the most dramatic betrayals in wrestling history.
Dear Zachary already starts off sad, detailing how Andrew Bagby was loved by friends but killed by his mentally-unstable girlfriend Shirley Turner. While she's about to go to trial for Andrew's murder, Turner reveals she's pregnant, and Andrew's parents attempted to battle to get custody of the baby. The film was meant to be a compilation of people talking about Andrew so that his son, the titular Zachary, would know him. But then, in a horrendously cruel twist of fate, Turner kills herself and Zachary. The rest of the film is about Andrew Bagby's parents getting justice for their grandchild through new laws that would keep people in Turner's situation (about to be on trial for murder) in prison before trial.
Death Proof is about a group of attractive girls hanging out at a bar who meet a mysterious older named Stuntman Mike. And then... he kills them all, and we move onto a different group of girls.
The Descent is somewhere between this and Developing Doomed Characters, as the film spends a while dealing with the personal interactions and physical hardships of a group of female spelunkers, then adds subterranean cannibals.
The main focus of the first half of Exam focuses on the candidates trying to unveil hidden writing on their paper. Then White makes Brunette burn her own paper, and the rest of the film documents the candidates slowly going insane and turning on each other.
Flightplan (2005) starts with a recently-widowed woman waking up on a plane with her daughter nowhere to be found with no one on the flight crew or among the passengers remembering a little girl. Soon, even she begins to doubt her own sanity, especially when the captain proposes that her daughter died along with her husband, and that she's in deep denial over this. After discovering that it's all a plot to blackmail the airline for a lot of money and frame her for it, the movie promptly turns from a psychological thriller into an action flick, where she tries to find her daughter, while trapped on a plane with a killer and his accomplice.
The former Trope Namer (back when the trope was named "From Dusk Till Dawn") and one of the premier examples is From Dusk Till Dawn. It starts off as a crime-thriller about a pair of brothers on the lam in Texas, who take a family hostage in their RV to cross through the border with Mexico. Halfway through, when they enter a strip club, they basically stumble into a slapstick-gore horror film of a similar premise to a Zombie Apocalypse, only with vampires instead of zombies. There were actually cinema-goers who said, out loud, at the point of the switch, "Wait, what the hell kind of movie is this?!"note Which is doubly strange, considering that the genre shift is more of a non-spoiler, as it was HEAVILY advertised as a creature feature as far back as the earliest trailers and promotional materials.
Funny People was advertised as a funny yet touching story of a famous comedian coming to terms with the value of his own life when he's diagnosed with a deadly disease. About halfway through the film, however, he's cured, and he spends the rest of the film getting entangled in a romance with his married ex-girlfriend.
Hancock, rather infamously. It starts as a comedy about a superhero who really sucks at his job. Then halfway through, it turns into a dramatic action movie when his PR person's wife turns out to be another superhero who was Hancock's former wife and they're both immortal.
Heckler starts out as Jamie Kennedy's examination of hecklers, in which he interviews comedians about their thoughts on heckling and confronts actual hecklers who interrupt his stand-up comedy shows. About halfway through, the film twists and starts going after movie critics in the same fashion, suddenly revealing its central thesis that critics are really just hecklers.
High Lane, another mountaineering film, turns into a Slasher Movie for its second half when its protagonists suddenly find themselves being hunted by a feral, cannibalistic Mountain Man.
Psycho starts out following a woman who succumbs to temptation and steals money from her employer. The film changes to a horror story about forty minutes in when she's murdered out of the blue by a psychotic motel manager, and the rest of the film follows him. Hitchcock threw his original audience off even further by hiring a well-known actress to play the Decoy Protagonist. To reinforce this trope, he requested theaters screening Psycho to not let any more people in to watch once the movie began.
The classic The Birds starts out as a romance and then shifts gears about half way through the movie, turning into a horror movie about the titular animals.
The driving plot thread of the first half of Vertigo is the mystery behind Carlotta Valdes and whether or not Madeline is possessed by her. The second half of the film (after Madeline's death) is centered around Scottie's obsession with Madeline and the lengths he'll go to in order to be with her again.
House of Flying Daggers starts out as a story about a soldier trying to infiltrate a rebel organization, with the implication that he's going to end up falling in love with the blind girl who is his only lead and have to choose between love and duty. Then the political aspects abruptly get discarded in favor of a love triangle story between the hero, the girl, and his boss.
Hugo spends a good chunk of its runtime detailing the life of the titual street urchin living in a train station, trying to figure out a way to fix an automaton found by his late father, but once he finds out that Papa Georges is actually Georges Méliès, most of the rest of the film focuses on his various real life exploits of working on silent films instead.
In Icarus, the documentary starts out with Bryan Fogel (the director) trying to win an amateur cycling race through doping and getting past testing as an experiment. The person he uses to help him with this, Dr. Grigory Rodchenkov, was (at the time) the director of Russia's national anti-doping laboratory. As they become buddies, it's revealed that there is a Russian state-sponsored doping program Grigory runs. As news of this program comes out in the media, Fogel flies Dr. Grigory to the States to testify about it while keeping him safe. The documentary is all about Grigory and the doping program from this point on.
In Imposter (2012), French career conman Frédéric Pierre Bourdin impersonates a missing boy - Nicolas Barclay — in order to get to the United States. Throughout the movie, he details all the crazy things he did to trick the family. He was eventually found out by several authorities (an FBI agent and a private investigator). Then the focus shifts to the family and how they were so inviting of a man who was obviously not Nicolas. The conclusion drawn by several people is that someone in the family killed Nicolas and everyone covered it up. The documentary ends on an uncertain note, though several family members plead to the camera that this is not the case and that Frédéric is a liar.
The Invention of Lying has this. The first half of the movie is about a man in a world where everyone tells the truth discovering he can say falsehoods and people believe him, and the second half turns into a commentary on love and religion.
A View to a Kill starts out with an investigation of Corrupt Corporate Executive Max Zorin and his sale of EMP resistant microchips to Soviet Russia. James Bond investigates by attending a horse sale, where he finds out that Zorin is also trading in illegal augmentations. Neither of these plot points make much of a difference in the end because right after Bond escapes, the real plan to destroy Silicon Valley is introduced and a relatively minor clue (a check made out to a woman from San Francisco) brings Bond to California.
Goldfinger starts as a surveillance mission to determine if the titular character is smuggling gold in and out of England to get the best price. Smuggling is forgotten quickly with the phrase "Operation: Grand Slam" which turns out to be a plot to nuke the gold at Fort Knox.
The Australian film Japanese Story is billed as a romantic drama involving an Australian scientist (played by Toni Colette) who ends up having an affair with a married Japanese businessman. About 2/3 of the way into the film, the businessman dies in a freak accident while swimming, and the rest of the film is spent on Colette's character dealing with the corpse and the aftermath of this man's death.
Jaws begins as a story about a small town police chief trying to convince the mayor that there's a shark and having to deal with the island being more concerned with the economic impact than lives. The second half is a three man buddy movie as the chief goes on a shark hunt with a grizzled old fisherman and a rich young scientist. We never see anyone from the town again until the sequel.
Killer Mountain starts off as a fairly standard mountain climbing drama/thriller, but then the remaining protagonists discover Shangri-La, an immortality serum, and monsters that are implied to have been left behind by Ancient Astronauts.
Stanley Kubrick did this a lot with his later films. It's actually a trademark of his that his films were split into two distinct halves, and it got to the point where he'd even explicitly label them.
2001: A Space Odyssey does this not once, not twice, but four times. The first plot focuses on the evolution of man, and then we switch to a plot centered on Dr. Floyd participating in a top-secret mission to the Moon which turns out to be because they had found the first conclusive evidence of extraterrestrial life. Then much of the rest of the film is switched over towards showing the lifestyles of the two conscious astronauts aboard a long-distance flight when some strange things happen, before taking a dark turn where Hal kills everyone except David Bowman at which point it becomes an incredibly surreal series of occurrences that lead to the next stage of human evolution.
Like the book it was based on, A Clockwork Orange was specifically divided into three parts. The first introduces Alex and shows us the dystopian world in which he lives as we see him and his droogs go out and do all kinds of nasty things. Then we get to the second plot centered around the experimental rehabilitation technique, and finally the third story where Alex must deal with the effects of the technique.
Full Metal Jacket starts off with Joker in boot camp, focusing on the decaying mental state of Private Pyle and his interactions with Gunnery Sergeant Hartman. After Pyle's murder-suicide, the film follows Joker to war.
Lake Bodom starts as an archetypal Slasher Movie (group of teenage friends go camping in the woods where unsolved murders occurred years ago, sexual tension and partying happen, people start dying) until the reveal that half of the group has been plotting to murder the others. The film then follows their effort to dispose of the bodies while extensive flashbacks explain their motives, until a second twist reveals that they are actually being stalked by a crazy murderer, and the film goes back to the slasher genre.
Letter Never Sent starts off as a story about four geologists trying to find diamond deposits in the forests of Siberia. The main plot conflict seems to be the Love Triangle between the pretty young female geologist, her boyfriend, and the older male geologist who covets her. Then the forest catches fire, the second half of the movie is a desperate struggle to survive and escape the burning hell, and the Love Triangle part is completely forgotten. (Even before Dwindling Party kicks in.)
Life Is Beautiful: Starts off as a romantic comedy, where Guido Orefice eventually wins the affection of Dora and they have a son named Joshua. Switch time — Let's send them all to a concentration camp! Guido tries to make the best of the situation for Joshua by telling him that if he doesn't complain/cry and hides from the guards he would gain "points". 1000 would win a tank. Just before the camp is liberated by the Americans, Guido gets caught by a guard and unceremoniously shot. The movie ends with an American tank at the gates to the camp, and Joshua exclaiming that he won. Damn you, Roberto Benigni.
The John Sayles film Limbo starts off as a movie about a fisherman in a small Alaskan town who starts a romance with a single mom and the trouble he has bonding with her daughter. Then they go on a boat trip with his wayward brother who is suddenly attacked and murdered by drug dealers the brother owes money to. The three characters are then forced to seek shelter and fight to survive on a nearby uncharted, uninhabited island.
Lost Highway by David Lynch is a particularly wild example. Out of nowhere, Bill Pullman simply turns into Balthazar Getty and a completely different story unfolds...but not really.
Mad Max: Beyond Thunderdome starts off as a typical post-apocalyptic action flick until Max is brought to the Oasis. Suddenly, the whole situation in Barter Town is left behind, and the theme changes to something akin to the Lost Boys from Peter Pan. Only when Max and the kids reach the Barter Town Underground are the two plots combined.
Miracle Mile: What starts out as an indie romance-comedy suddenly takes a right turn when the male lead picks up a ringing payphone and someone at NORAD tells him that World War III has begun and the missiles are on their way. The rest is about finding his love interest, telling other people that the city is about to be nuked and figuring out how to escape and survive the end of the world.
The Sidehackers starts as a lighthearted sports movie, but about a third of the way through it turns into a gritty revenge film after the rape/murder of Rommel's girlfriend. The Brains decided to vet the movies they chose to riff more carefully in the future after this one.
The Girl in Lovers' Lane shifts gears after the girl from the romantic first two-thirds of the film is outright murdered half-way through the final act.
To the extent that Napoleon Dynamite has a plot, it pulls one of these. There's little plot to be seen in the first half, but once Pedro decides to run for school office, most all focus goes to his campaign.
The "Oedipus Wrecks" segment of New York Stories has the Woody Allen character's Beloved Smother vanishing during a disappearing act of a magic show. Audience expectations are subverted, however, when she appears as a giant head floating over Manhattan, to torment her son in front of the entire world.
The Rupert Everett and Madonna movie The Next Best Thing starts off with a rather sweet and interesting idea about a gay man and his female friend who have sex after a night of drinking and she becomes pregnant — they decide to raise the child together. The second half of the movie veers unexpectedly when Madonna's character reveals that Everett's character isn't the real father and she wants full custody. Cue courtroom drama.
The first half of Parasite (2019) is a Black Comedy about the poor Kim family conning their way into cushy jobs working for the rich Park family. At the halfway point, the Parks go out of town for a night. This allows for the former housekeeper (whom they'd gotten fired by making it seem like she had TB) to get back to the house. This is when the Kims find out that she's been hiding her husband in the secret basement for four years and at that point it becomes a thriller.
The little known 1988 film Permanent Record spends about twenty minutes convincing you it's just throw away teen angst when the kid we thought was the protagonist leaps off a cliff to his death between jump cuts.
The Thai horror film Phii Khon Pen (called The Victim in the US) starts as a movie about an aspiring actress who gets a job playing the victim in crime re-enactments and landing the role of a murdered supermodel, only to become caught up in the investigation of her death when the real model's ghost begins haunting her. Just as that mystery is solved and the plot comes to a climax, it's revealed that we've been watching a movie-within-a-movie. The plot then switches to following the cast and crew of the movie we've just watched, who are experiencing real supernatural events on the set, which they believe to be related to the true story they based their film on. By the end, it turns out the haunting of the film set actually has nothing at all to do with the story of the movie-within-a-movie after all.
The classic Predator starts with Arnold Schwarzenegger trying with his fellow soldiers to save a US politician from a band of South American terrorists. After he discovers that this was just an excuse to save some Black OPS agents, this plot is conveniently thrown out of the window when an alien with an explosive plasma Shoulder Cannon and a cloaking device begins hunting them. Unlike some other examples, this wasn't a surprise to original audiences, and the film begins with something falling to Earth from space and the team encounters the remains of the alien's previous victims early in the film, albeit first under the impression it was the terrorists who did it.
Private Benjamin starts out as a story about a woman making it through basic training, but mid-way through the movie, she's not even in the Army anymore and the conflict revolves around her and her lover.
''The Queen of Versailles" starts as sort of a puff piece on Time-Share magnate David Siegel and his wife Jackie, as they construct the Versailles House (which would be one of the largest, most expensive homes EVER). Then the Great Recession of 2008 hits and we see their family struggle to adjust as David's company takes some huge hits.
Rat Pfink A Boo Boo. The plot was altered during filming to accommodate anything and everything that passed through the director's hands. Most notably, when a gorilla suit became available, they wrote a gorilla into the movie. It suddenly shifts from being a gritty crime drama to a superhero spoof.
The Sound of Music. A cute heart-warming family-friendly musical romp about a nun-turned-governess who teaches her wards the joy of music, and redeems their father, winning his love. And look, at the two hour mark they marry in a show-stopping number. Cue end-credits any time n— oh wait no, that's right: Nazis. Cue 45 minutes of defiance, heartache, quislings, and dark reprises.
Space Cowboys starts out as a comedy about a group of elderly former astronauts training to go back into space on the space shuttle. The second half of the movie suddenly becomes an Apollo13/Armageddon-esque thriller where the same elderly astronauts have to deal with the revelation that the "communications satellite" they were sent to repair is actually a nuclear weapons platform, a malfunctioning craft and find a way to get back to Earth safely.
The first half of Spider-Man: Far From Home features Spider-Man teaming up with Mysterio to defeat the Elementals, while the second half reveals he's the Big Bad and the Elementals were just illusions.
Star Wars Episode VII: The Force Awakens starts as a search for the now-reclusive Luke Skywalker by both the Resistance and the First Order. But halfway through the movie, Starkiller Base, the First Order's new Death Star-style superweapon, is introduced to provide an ersatz Death Star for the finale.
The first half of Stripes deals with the irreverent recruits just barely pulling it together to pass boot camp. The rest is about their first mission as they're sent to Italy to recover a militarized RV.
Submarine: The first half is about the development of Oliver's romance with Jordana, which then shifts abruptly to Oliver investigating his mother's infidelity.
Tokyo Zombie: The first half of the movie centers on the main characters trying to escape the zombies on the streets of Tokyo. Five years later, and it's set in a bizarre society controlled by the rich, and Fujio is now a professional 'zombie-wrestler'.
Trail of the Pink Panther's (1982) first half has Inspector Clouseau investigating the latest theft of the Pink Panther diamond. Then he goes missing, and the film switches to the adventures of a TV reporter investigating this via interviewing his friends, foes, and family. Why? Clouseau's actor Peter Sellers died in 1980, before this film was written, and his scenes in the first half are mostly-deleted scenes from The Pink Panther Strikes Again put into a new context. The second half boils down to a Clip Show of the previous films. All of this sets up the next film, Curse of the Pink Panther (1983), which introduces a new protagonist and leads up to the revelations of what happened to the diamond and Clouseau.
The Paul Giamatti film Win Win starts out as a comedy about high school wrestling with Giamatti coaching a young wrestling prodigy...then the kid's mother shows up and the second half becomes a drama about a battle over an estate. It still works though due to Giamatti and Tom Mc Carthy's direction.
The World's End starts off as a rather bittersweet comedy about a forty-year old Manchild screw-up getting his high school gang back-together to try and complete an incredibly difficult pub crawl. Then, about half-way in, they discover their old town has been replaced by alien replicants, and it turns into a sci-fi action flick.