In the Alien franchise. This is basically what happens to a Xenomorph Drone or Warrior, when they are chosen as the new Queen of the hive. Male Xenomorph Drones and Warriors change gender and become female to be the new Queens of their Xenomorph hives.
Sir Bernard Cutting in Carry On Matron has his body examined by Dr. Pearson, a fellow doctor at Finisham Maternity Hospital, who points out that his pelvis is rather feminine-shaped, which makes him think that he is probably gender-bending. Unsurprisingly, this trope is subverted, but he soon relaxes after visiting the cuckoolander Dr Francis A. Goode, who's just as uncertain about the situation as Sir Bernard is.
In the late-night exploitation film Cleo Leo, the lecherous Leo Blockman is shot and falls into the river. He later emerges down-river in the body of an attractive female, and later goes by the name Cleo Clock.
The Australian feature Dating the Enemy takes the classic set up of a bickering couple, Tash and Brett who get an opportunity (in a "Freaky Friday" Flip) to "see the world through the other's eyes".
Deathstalker: Gargit is transformed into Princess Codille instantly via magic. He is sent to seduce and kill the Deathstalker.
There are several films which take the story of Dr. Jekyll and Mr. Hyde and, while keeping Jekyll male, have Hyde be a beautiful but evil woman:
The soft porn film The Adult Version of Jekyll and Hide has modern day Dr Christopher Leeder try recreating Jekyll's formula, only to turn into an attractive female Miss Hide.
Hammer'sDoctor Jekyll and Sister Hyde, exploited the startling similarity in appearance of leads Ralph Bates and Martine Beswick. This is mostly a retelling of the original with the Gender Bender twist.
Played for Laughs in Dr. Jekyll & Ms. Hyde, Doctor Jacks is a modern day chemist who inherits the scientific notebooks of his great grandfather — Henry Jeckyll. The resulting formula turns him into Ms Hyde.
The obscure spoof Dr. Heckyl and Mr. Hype, has modern day podiatrist Dr. Heckyl turning into the handsome debonair sociopath Mr. Hype after drinking a weight loss formula. Dr. Hoo also drinks the formula, but is turned into a woman, a virtual twin of Miss Finebum. And, there is a scene where Dr. Heckyl has a string of Photo Montage transformations, including some as a woman.
In Hammer'sFrankenstein Created Woman, Doctor Frankenstein successfully transfers the soul of Hans into the just-drowned body of the deformed Christina. Frankenstein fixes up the woman's body, making her beautiful, but as with most of the Doctor's experiments, things start going downhill from there.
Freaky: For the Butcher and Millie via "Freaky Friday" Flip. He's an adult man, she's a teenage girl, and both find the change discomforting (he adjusts faster).
In The Gamers: Dorkness Rising, male player Gary chooses to play the game as female sorceress Luster, based in his head on his hot math teacher. Unfortunately, he keeps forgetting the sex of his character, and "in-game" Luster is constantly switching between male and female. It's lampshaded several times, both in-character and out-of-character.
A female to male version, in the 2015 Swedish film Girls Lost — based on the Young Adult novel Pojkarna by Jessica Schiefauer — three teen girls, Momo, and Bella who suffer from misogynistic bullying at school find a mysterious seed that grows into a flower that can turn them into boys if they drink its nectar, though it wears off by morning. Kim is heavily hinted to be a trans man and finds the situation liberating and becomes addicted to the nectar, whilst the other two are intrigued and find some more confidence as boys, but admit they'd rather stay as girls.
In Goodbye Charlie, womanizer Charles Sorel is shot by a jealous husband and falls out a porthole. He's lost at sea only to find himself returned as an attractive blonde woman.
In Gozu, a dead Yakuza brother Ozaki returns as a young attractive woman with no explanation given why.
Gremlins 2: The New Batch: One of the Gremlins ingests a jar of Applied Phlebotinum in the genetics lab that immediately turns it into a Girl Gremlin, who then proceeds to become an Abhorrent Admirer to the jerkass head of security. This is one of the more peculiar examples by the standards of the trope, since the Gremlins are an asexual species that reproduces more like a fungus.
The Hong Kong action comedy Holy Weapon features this towards the end. In the movie, Ghost Doctor creates "Feminine Wine" for an intersexed woman Yam Kin Fai, warning that if a man drinks even just a drop, he'd become a woman. They then have the male Idiot Hero Ng Tung look after the brew without telling him what it is or what it does. Ng Tung unwittingly drinks the brew, thinking it's a nutritious soup. Then his penis tells him that from now on, whenever his body gets wet, he'll turn into a woman. He'll become a man again when he dries his body. This becomes useful during the final battle, when the Big Bad's Mooks throw Ng Tung into the river as a sacrifice, only for him to emerge fully female, complete with bouncing chest and Girlish Pigtails. Thus, he/she becomes the Seven Virgins' 11th-Hour Ranger (since one of them is trapped in a net throughout the battle). Rather than switch to an actress, actor Wai-Kin Cheung was made up to look like a girl.
The Hot Chick has a lowlife thief Clive Maxtone accidentally swapping bodies with a snotty teenage girl Jessica Spencer.
The Fox Family TV movie Ice Angel (released on DVD in Australia as On Thin Ice: Going for the Gold) is about a male hockey player Matt Clark who dies prematurely and is brought back to life in the body of a female figure skater Sarah Bryann so he can win the Olympic gold medal that he was supposed to win the first around. It's actually a remake of Here Comes Mr. Jordan (1941) (like the film Heaven Can Wait (1978) and stage play Heaven Can Wait (1938) by Harry Segall), with the Gender Flip adding Different for Girls as an added complication on top of the original's Fish out of Water hijinks.
In Identity Theft, Matt Walker, who recently won the lottery encounters Karen Bristol and has a one-night stand. When he wakes up he finds they have exchanged bodies. He's a victim of someone who swaps bodies at will, mostly to prolong life indefinitely, but in this case it's done to collect his lottery winnings. Later, Lisa Tate will switch bodies with Collette.
The movie Jumanji: Welcome to the Jungle is about a group of teenagers who get sucked into a video game and are stuck in the bodies of the avatars they chose. The group's wannabe Alpha Bitch, Bethany, ends up selecting Professor Shelly Oberon, whom the game describes as a "curvy genius" (which she assumes means "hot scientist"). To her surprise and horror, Shelly Oberon turns out to be an overweight middle-aged man played by Jack Black. Hilarity ensues.
Spencer re-enters the game, hoping to regain the confidence he had as Dr. Smolder Bravestone. However, the game sticks him with the avatar of female thief Ming Fleetfoot. To add insult to injury, Fleetfoot has essentially the same strengths and weakness as his real world self: high intelligence and cleverness, but no physical strength or fighting skills — and a pollen allergy to boot.
Later, Spencer's grandfather, Eddie, ends up in Fleetfoot's body; he's too amazed by the fact that he has a full head of hair (being bald in the real world, and having spent much of the film as the extremely strong, but bald, Bravestone) to be concerned about being female.
"Fridge" initially gets stuck as Professor Oberon (which, as the group's resident jock, he is not happy about). However, an electric shock causes him to briefly swap avatars with his teammate, Martha, putting her in Oberon's body and him in the body of Ruby Roundhouse (which he finds far preferable). After he admits that the breasts are a nice bonus, Martha snaps at him to keep his hands off her body; Fridge replies that feeling himself up was the first thing he did.
Bethany, who enters the game long after the others, ends up with the only remaining avatar: Cyclone, a horse. After that, she's only too happy to be swapped into Professor Oberon's body (again).
In the Italian comedy Le Comiche 2 the two main characters cause physical and psychological damage to many people throughout the multiple episodes composing the movie. The main recurring victim is a male individual that undergoes an undesired breast augmentation at the end of the first episode. Later he has an accident of Comedic Underwear Exposure, revealing he is wearing a bra supporting large breasts. As the movie progresses, he ends up in a hospital and he is given a sexual reassignment surgery. Finally, completely turned into a woman, she is an odalisque in a harem, seemingly accepting her new role and gender (Second Law of Gender-Bending).
The TV Movie The Magic Statue was made by combining episodes 1, 2, 5, and 7 of the short-lived TV series Turnabout. In this movie, Sam and Penny Alston eventually have their bodies swapped back and end up believing they had had a strange shared dream.
In the TV movie (filmed stage play) The Marvelous Land of Oz, the boy Tip transforms into Princess Ozma.
In Orlando, the title character wakes up as a woman halfway through the movie and is completely unfazed by the change, which is more than you can say for everyone around her.
In the Phantasm films, the Tall Man is able to transform himself into Lady in Lavender or Alchemy in order to lure people in to be killed. The Tall Man's Lady in Lavender persona appears in Phantasm, Phantasm III, and Phantasm Ravager. In Phantasm II Alchemy is mysteriously replaced by The Tall Man in the end.
To everyone living, Roy looks like a beautiful young woman. This leads to some comedy moments where we see Roy (who still looks like Jeff Bridges to us) having to fend off men hitting on him. Later we see Proctor has a male avatar, and Nick's second avatar is a Girl Scout.
In the Prequel film (R.I.P.D 2: Rise of the Damned), Roy's first avatar is a young black woman.
In Sam, womanizing misogynist Sam is transformed into a woman thanks to a mysterious tea he drank at The Little Shop That Wasn't There Yesterday. He is absolutely horrified at the transformation at first, even considering getting gender reassignment surgery to transition back to male but backing down after learning everything that would entail. By the end of the movie, she gets the opportunity to change back, but declines as she's realized she's more comfortable as a woman.
In Scooby-Doo (2002), the gang's souls switch bodies at one point. Fred and Daphne switch bodies first. After that, Daphne gets her body back, but Fred inhabits Shaggy while Velma inhabits Fred and Shaggy inhabits Velma. Next, Velma inhabits Shaggy, Daphne inhabits Fred, Shaggy inhabits Daphne, and Fred inhabits Velma. Then, finally they return to their correct bodies.
In Scooby-Doo: Monsters Unleashed, Shaggy drinks an unknown potion and transforms (from the neck down) into a woman, for a little while. This turns out to be a Chekhov's Gun as the villain was using it to disguise his identity.
Secret Garden (2012) is a Chinese stand-alone film adaptation of the Korean TV series Secret Garden (2010-2011). A wealthy CEO and a stuntwoman have their bodies switched by a magical painting. In the end, things are resolved for that couple, but then pop star Oscar and his female director are looking at the same painting and have their bodies switched.
The plot of The Sex Trip is that Eddie is turned into a woman through a witch's curse, and he spends a bulk of the movie as "Edna".
In the soft porn sex comedy Sexual Chemistry, a chemist's attempt to create a sex-enhancing drug backfires, turning him into a woman. He keeps changing back and forth over the course of the movie. Hilarity Ensues.
Something Special (a.k.a. Willy/Milly) is a female-to-male example, where a tomboyish teenager wakes up to find herself magically transformed into a male after making a wish during a solar eclipse.
In Splice, Ginger, one of the two transgenic creatures created by Clive and Elsa, turns from female to male due to hormonal changes, and fights Fred (the other transgenic creature, who was male from the start) during a press conference that unleashes a shower of blood on the front row. This turns out to be foreshadowing for similar changes in Dren.
Stardust: The goat herder Bernard is transformed into a woman in order to pose as Lamia's daughter for the fake inn she created. He almost immediately tries to feel himself up, but Lamia stops him. He does however to get enjoy helping Yvaine undress. However, Lamia either couldn't or didn't bother changing what his voice sounds like, helping tip Tristan off to the inn's true nature.
In Disney's The Swap, two high school students are using cell phones with such extreme sentimental value that they have become "totems". They make the mistake of texting each other the wrong thing, and the phones switch their minds into each others' bodies. They can't get the phones to change them back until they resolve each others' issues, and in the mean time also try to win at each others' sport.
Switch (1991) is a loose remake of Goodbye Charlie with a bit of Here Comes Mr. Jordan (or Heaven Can Wait (1978)) mixed into the plot. Steve is shot by one of his girlfriend conquests and must return to life and find at least one female who likes him, or it's eternal punishment for him. As an added twist, Steve is returned in the body of an attractive female.
The Belgian short erotic art film Switch 2018 features an initially female protagonist who discovers that having an orgasm causes her to change sex. Later in the film, she meets a guy who becomes female when he has an orgasm. The film can be seen as a commentary on trans people's experiences. Can be viewed here.
The 1940 Hal Roach feature Turnabout concerns a bickering husband and wife, each of whom wishes they could have the "easy" life of the other gender. Their wish is subsequently granted by an enchanted Indian sculpture sitting on their mantelpiece. The body-swap is further complicated by Voices Are Mental, with a man's voice coming out of a woman's mouth, and vice versa. By the end of the film things are seemingly back to normal... until the Indian god confesses that he screwed up and informs the husband that he's now pregnant. The film was an adaptation of Thorne Smith's 1931 novel, which was later adapted as a short-lived TV series in 1978.
Zerophilia, directed by Martin Curland, concerns a young man named Luke who discovers he has the rare Z chromosome after his first sexual encounter with a woman travelling in a camper. (Apparently, he never tried masturbation.) This gene makes him a zerophiliac, a person whose sex changes with the act of sex (either by your lonesome or with another person). Sex with another zerophile induces mode locking, after which the zerophile will only change sex when having sex with another zerophile. We meet three different zerophiles — Luke/Luca, Dr. Sydney Catchadourian (using the name for both sexes), and Michelle/Max.
