An Alternate Reality Episode is slightly different from an episode that incorporates an Alternate Universe.
In an Alternate Reality Episode, the usual main characters are absent. The main cast is still here, but they're playing "themselves" in a different role. Maybe Alice is now a Dot Com boom millionaire instead of a lowly research assistant, or the other way around. The point is that it's our heroes being different people, not the same people visiting a different place.
Typically, the "normal" situation may get a look-in for a couple of scenes at the start or end of the episode, but there should not be any clear link between the characters - Alice the millionaire should not wake up as Alice the research assistant, or have Bob her millionare buddy visiting her, asking why everything is different.
Compare with Parody Episode (this trope could be considered the serious side of the coin) and Elseworld. This may be a Mirror Universe episode where we see what the cast would be like if they were evil (especially in Star Trek).
- Neon Genesis Evangelion Episode 26 has what is more of a Alternate Reality Segment, but it plays out like such an episode none-the-less, showing a world where the series, instead of being a Science Fiction Mecha Drama set After the End, is a Slice of Life Romantic Comedy set in a perfectly normal (well, normal by anime standards) High School. The segment plays out in-universe as an attempt to show Shinji that he could lead a happy life without being an Evangelion pilot.
- In an anime only episode of Ranma ½ Ranma and Akane are discussing how Genma is away training for way too long. Meanwhile Genma fell off a cliff and into a river. Then in his panda form he's found by who he believes to be Ranma, Akane and Kuno. However they don't recognize him and call themselves Kotaro, Kanna and Hayato. Soon he's welcome as a prophesized lucky panda to the feudal-esque town where almost the entire main cast except himself exists, with similar relationships. He helps Kotaro and Kanna defeat Hayato and makes them hold hands, prompting the family and villagers to cheer them into marriage. He's then accidently knocked off another cliff and he returns home and makes the real couple hold hands too. No explanation is ever given about this alternate reality.
- Big Finish Productions produced the Doctor Who Unbound audio drama "Deadline," a Doctor Who story on the question "What if Doctor Who had never existed?" It's ... meta.
- "The Unwritten Fables", the final arc of The Unwritten vol. 1, crosses over with Fables in an alternate reality where Big Bad Mr. Dark was never defeated and the remaining Fables are constantly on the run.
- Mirrored, the IDW comics' New-Trek-Movieverse version of "Mirror, Mirror" had more in common with Star Trek: Enterprise's "In A Mirror Darkly" than the Original Series episode. It opens and closes with "our" Scotty and McCoy discussing the concept of alternate universes, and the rest of the story is set entirely in the Mirror Universe, with no "real" characters. (Well, Old Spock seems to have come from [a version of] the regular universe rather than the mirror one, but he's still not the same Old Spock.)
- DC Comics pretty much specialized in this form of storytelling, publishing dozens of stories from the 1950s onwards where, either as a one-off "change of pace" storyline or as a back-up story "filler" (common in the days when some issues ran for 80-100 pages without ads in some cases, and needed to be filled). In the 1980s, DC launched its "Elseworlds" line, with followed the same concept, except usually with more serious stories.
- Marvel Comic's take on alternate reality storytelling was its long-running What If? title.
- The Last Dragon Chronicles: Fire World.
- Fire Ascending goes through quite a few.
- On season 7 of The Big Bang Theory in the episode "The Cooper Extraction", the main characters explore the ways that Sheldon has changed their lives through a series of "What if" clips.
- Bones has done two. In one, Booth and Brennan were married and owned a nightclub (called "The Lab") where many other series regulars worked. A murder takes place there, and we get to see Brennan squicked out by death. This is actually a dream of Booth's, while he is in a coma. It's actually his perfect world and based on Brennan talking out loud to him in his coma while she works on her next book. The other recast Brennan and Booth as, respectively, a police officer and a jewel thief in a 1950s Hollywood-style setting who forge an uneasy alliance in order to catch a murderer. Other series regulars appeared as coworkers and acquaintances of Booth's and Brennan's, with Brennan's father cast as the police chief and her boss as well as her father.
- Buffy the Vampire Slayer:
- Played terrifyingly in "The Wish". Cordelia, bitter over her failed relationship with Xander, makes an idle wish that Buffy had never come to Sunnydale, believing that her popular status would still be intact if she had never gotten involved in the Scoobies' affairs; unfortunately, she speaks in front of a disguised vengeance demon who grants her wish to the letter. Cordelia is tossed into a crapsack alternate universe where the Sunnydale population is a tenth of what it was, due to unchecked vampire attacks, due in turn to the Master having ascended a year and a half before without Buffy there to stop him. Cordelia is killed by evil vampire versions of Willow and Xander, Giles and Oz are trapped in thankless work as desperately outnumbered vigilantes attempting to do what they can to restore some semblance of safety to the community, Angel is kept in a cage with the Master's minions allowed to torture him for fun, and Buffy eventually makes an appearance as a hardened, pitiless rogue Slayer who has gone off the deep end without her friends' humanizing influence. The episode ends with a vicious Final Battle in which the entire main cast kills each other; Giles' last-minute actions save the day and propel everyone back into their proper reality, but it's still incredibly frightening.
- Dopplegangland was a play on this trope. Vampire!Willow from the alternate reality of The Wish accidentally finds her way to the real world, setting some serious foreshadowing for further seasons.
- Played with in "Tabula Rasa", where Willow casts a spell intended to remove Tara's memory of breaking up with her but instead blanks out everyone's memories including her own. They're in the same universe but because they're all starting from a blank slate they reach some very different conclusions about themselves. Giles and Anya think they're married, Spike thinks he's a vampire with a soul (usually Angel's role) and Buffy finds being a Slayer cool.
- Normal Again had Buffy, under the effects of a demon's venom, flashing between the normal Buffyverse, and an alternate universe where she had spent the last seven years catatonic in an insane asylum in Los Angeles, where they have been trying to treat her for her insane delusions about fighting vampires. The episode makes no attempt whatsoever to clarify which, if either, of Buffy's perceived realities are the real thing.
- The spin off Angel had "Birthday", where Cordelia got a chance to make her life what it would have (or should have according to the one offering her the choice) been like if she had met a big-time talent agent instead of Angel in the pilot. She becomes famous but Angel gets the visions (because Doyle still died) and it drives him mad. Wes and Gunn are with him, but with only three arms between the two of them.
- An odd variation on this trope occurs in the Community episode "Remedial Chaos Theory". Jeff throws a dice to decide who goes to get pizza, and the time-line splits into seven different universes. While some of the differences are relatively small (e.g. in one universe Troy and Britta fall for each other much earlier, while in another Britta hooks up with the pizza delivery guy) one of them is extremely horrible. When Troy gets the pizza, Pierce gets shot in the leg and dies, the apartment catches fire, Troy eats a flaming troll doll and loses the ability to speak, Jeff loses his arm, Shirley succumbs to alcoholism, Annie gets committed to a mental institution, and Britta dyes a streak of her hair blue. Abed dubs this "The Darkest Timeline" and makes everybody fake beards.
- Doctor Who: In "Turn Left", an alternate universe is created around Donna Noble where she never met the Doctor, and as a result, he died that Christmas stopping the Racnoss Empress, which led to Donna losing her job, although she did win a trip out of town for the next Christmas. Good thing, too, because without the Doctor there to help London was nuked and everyone in the city died. Because he wasn't there, almost everyone in the Royal Hope Hospital suffocated when it was transported to the Moon, including Martha Jones — who never met the Doctor in this timeline — and Sarah Jane and her friends, who stopped the sabotaged MRI from going off. It goes From Bad to Worse: The Doctor and Donna weren't there to stop the Adipose, and tens of millions of Americans were killed. The Sontarans nearly succeeded in rendering the planet inhospitable, saved only by the heroic sacrifices of the Torchwood team. And then the stars go out.
- The Flash (2014) starts its third season with Flashpoint, wherein Barry Allen went back in time and stopped his mother from being murdered. In the resulting timeline, Wally West is the Flash, Joe is an alcoholic who isn't in touch with his kids, Cisco is a billionaire who wants nothing to do with metahumans, Caitlin is a pediatric optometrist, and the city is being terrorized by a speedster named The Rival. Flash eventually is forced to revert the timeline, only to find himself in one that is merely a Close-Enough Timeline, which is played for much angst, as the new timeline features Cisco's brother dying in a car wreck, John and Lyla's child being a little boy named John instead of a girl named Sara, Caitlin being a metahuman, and Iris not talking with Joe.
Joey: *looking at food* "How YOU doin'?"
- "The One That Could Have Been" is a two-parter where the teaser has each of the Friends imagining something that could have happened differently in their lives and the rest of the story drops into an Alternate Reality where these things happened. Monica never lost her teenage weight and is still fat as an adult, Joey is still on Days of Our Lives and has become famous and wealthy, Rachel married Barry and is quietly miserable (and considering having an affair with Joey the celebrity), Phoebe is a stockbroker, Chandler is a (failing) writer and Carol has not come out of the closet and is still married to Ross (Though she is very interested in having a threesome with Ross and another woman).
- There's a sequence in "The One With The Truth About London" where Monica confesses that the night she hooked up with Chandler in London, she actually went to the room to seek out Joey. They imagine what life would've been like with those two together, in which Joey is fatter than young Monica, thanks to her cooking.
- Grey's Anatomy has the episode "If/Then", revolving around Ellis Grey being both alive and lucid. There are fairly significant ripple effects (Alex has proposed to Meredith; Callie and Owen are married; the Shepherds are still together; Cristina has no friends) but Because Destiny Says So other things come back to bite them (Alex is still an inveterate womanizer; Mark and Addison are still carrying on; Meredith still can't please her mother; she and Derek are attracted to each other; she and Cristina become Fire-Forged Friends whilst struggling to save a patient, Callie and Arizona are drawn to each other), turning the whole thing from "For Want of a Nail" into "In Spite of a Nail" instead. Incidentally, the episode's theme is "Because Destiny Says So." Has a lot of moments of This example contains a YMMV entry. It should be moved to the YMMV tab.Fridge Brilliance.
- Hercules: The Legendary Journeys had an episode where Iolaus traveled to a parallel universe where Hercules is an evil tyrant, Ares is the god of Love and the other gods are of different things than they usually are.
- Season One of Heroes had "Five Years Gone"; an alternate timeline that spiralled off from the explosion in New York, turning the United States into a prejudicial dystopia who regards almost everyone with abilities as terrorists. Claire has dyed her hair and got engaged in an effort to stay in hiding, Noah Bennett has left the Company and become an almost Underground Railroad-esque assistant for people with abilities, Hiro Nakamura becomes an icy, sword-wielding vigilante while Nathan Petrelli becomes the President... until it's revealed that he was actually killed shortly after his inauguration by Sylar. By this point, he had gained possession of Candice's illusion ability and set about using it to take Nathan's place and drive the country into the ground to eliminate his "competition".
- Las Vegas: There's an episode where Danny imagines himself and his co-workers working at a Las Vegas casino in the 1960s instead of the 2000s. Ed Deline is basically a mobster-turned casino boss as opposed to an ex-CIA agent turned casino manager, Mike faces racism from a Jerkass diner owner, and Sam Marquez is a hooker operating out of the casino.
- Half of each episode of Lost Season 6 is devoted to a alternate reality where the plane never crashed, which apparently resulted from the cast's attempt to change history in season 5, while the other parts of the episode continue as normal. The two timelines seemed totally independent for a while, but now certain people in the "flash-sideways" timeline, particularly those with love interests, have begun having visions of the island timeline... Ultimately, the alternate universe proves to be a cross between a Dying Dream and Mundane Afterlife.
- Mad About You: In "Up In Smoke" the newsstand where Paul and Jamie first met has burned down, pushing them into a reality where they never meet, though Jamie briefly dates Paul's cousin John.
- The second season of Nip/Tuck has an episode where Julia dreams what life would be like if she'd married Christian instead of Sean. In the alternate reality, she and Christian are partners in the "Troy/Troy" plastic surgery firm, Matt (still raised by Sean) is a nerd, and Sean is married to a still-living Megan O'Hara.
- Season 6 episode "The Decision" of Scandal has Olivia imagining what life would have been like for the main characters if she hadn't made a critical decision prior to the beginning of the series.
- The Sherlock Christmas Special "The Abominable Bride" mostly takes place in a What If? scenario entirely in Sherlock's "Mind Palace" (with a "healthy" doze of drugs). It's a more traditional take on Sherlock Holmes, taking place in Victorian England, investigating the case of a woman who publicly committed suicide and then keeps appearing and killing men. This is all Sherlock's attempt to figure out how Moriarty could have possibly survived shooting himself in the head a foot away from Sherlock. He comes to the conclusion that Moriarty is, of course, dead, but he has set events in motion prior to his death that still continue to unfold.
- Stargate Atlantis: "Vegas", the penultimate episode of the series, takes place in an Alternate Reality where John Sheppard is a Las Vegas detective and never joined the Atlantis expedition. There is a brief crossover (a message sent from that universe enters the main one), but no characters crossover. It is sometimes referred to as CSI: Atlantis, which was actually its working title during production.
- Star Trek:
- Star Trek: Deep Space Nine has the episode "Far Beyond the Stars", where the cast are reimagined in 1950's New York. Sisko, Kira, Julian, Bashir & Quark are all writers for a science fiction magazine. Odo is their boss, Jadzia is his secretary and Martok is their artist. Cassidy is a waitress at a local diner, Jake is a petty criminal, Worf is a professional athlete, Weyoun and Gul Dukat are a duo of racist police officers and grandpa Sisko is a priest and possible hallucination. When Martok's counterpart shows "Benny" a sketch of Deep Space Nine, Benny decides to write a story about it. It is rejected for featuring a Black Captain, one Benjamin Sisko. Benny attempts to get the story published result in him developing an obsessive attitude towards his Deep Space Nine stories and eventually having a breakdown due to his powerlessness against the racist society around him. Sisko thinks of the whole thing as a vision from the Prophets about "fighting the good fight" even when things feel hopeless. Interestingly, despite each of the actors playing a character distinctly different from their main role, each still has elements of the original. Quark's counterpart is the most vocal supporter of publishing Benny's story and has a strong social conscience, yet he is still convinced to stay with the magazine after haggling for a pay rise and being called a socialist is his Berserk Button, for example.
- In later seasons, following a surprise narrative return to the "Benny reality", it is left ambiguous as to whether that reality might truly be the real one.
- The Star Trek: Enterprise episode "In a Mirror Darkly" is an Alternate Reality Episode set in the Mirror Universe right down to having a different Title Sequence (there is a crossover from the regular universe driving much of the plot, but it's not from Enterprise, and it's not a regular or even a character as such), whereas the Original Series' "Mirror Mirror" and the DS:9 Mirror Universe Episodes are not, instead featuring one or more of the regular cast crossing over and interacting with the Mirror Universe.
- Supernatural has an episode where Sam and Dean are new employees at a hi-tech company, but have false memories of their lives and don't even know each other. While investigating a series of suicides at their company, they come to the conclusion that a ghost is involved and hunt it down. This leads Sam to first suggest that they should continue as ghost-hunters, and then realise that their whole apparent lives are fake. In the end, it turns out to be an illusion created by the angel Zachariah designed to inspire the broken Dean to continue the life of a hunter..
- Switched at Birth
- In "Ecce Mono," John imagines that Regina came clean about discovering the switch in 1998 but lost custody of the girls due to her drinking. Daphne is raised with the Kennishes, getting an cochlear implant to help her hear and not identifying as Deaf - but is a manipulative brat. Bay is now a studious young woman who falls in her sister's shadow; Toby is still gambling, and Kathryn is having an affair with another man (Chip Coto) The girls grow up thinking that Regina stopped contacting them altogether. She actually has tried to make contact with them their entire lives, but the Kennishes stash away the letters and presents instead of giving it to the girls. When they find this out and go to find Regina, they instead only find Adrianna; they find out from her that Regina died of drinking on their birthday.
- In "Yuletide Fortune Tellers," the girls are upset about their families' Christmas traditions only to wake up in a world where the switch never happened. Daphne is Bay, a star athlete with Toby a moody musician and John and Kathryn having marriage problems. Bay is Daphne, raised with a younger brother but Regina still drinking and Emmett only a friend.
- In the two-part 3rd Rock from the Sun episode "Dick'll Take Manhattan", the aliens go through a time-space portal to a parallel universe where they lead upscale lives in New York City. Dick is a lawyer, Sally is a columnist in the vein of Sex and the City, Tommy is a cast member on Saturday Night Live (with then cast members Tracy Morgan, Ana Gasteyer, and Darrell Hammond appearing as themselves), and Harry is the president of NBC. Other characters from the show turn up as well, all leading different lives of some description. Inevitably, the Solomons return home after finding their new lives to be shallow.
- An episode of Ugly Betty has Betty getting knocked out and dreaming of a world where she has the "perfect smile" and never needed braces. In this world Ignacio is a wealthy gambler, Hilda is the ugly sister, Justin doesn't exist, Amanda is married to Daniel but sleeping with Tyler, Marc is a homely receptionist and Betty is Wilhelmina's Alpha Bitch assistant.
- In the third season Christmas special for Warehouse 13, Pete is pulled into a world where he was never born, leading to Myka arresting Artie, Claudia never leaving the psych ward, and MacPherson taking over the Warehouse.
- On Wings, an episode features fantasy sequences in which the cast enacted "When I Grow Up" letters that their characters wrote when they were children.
- Xena: Warrior Princess saved the Fates in "Remember Nothing" and was given a chance to live her life if she had never become a warlord and "When Fates Collide" when Caesar forces the Fates to change his fate making him and Xena rulers of Rome.
- In an episode of Austin & Ally called "What Ifs and Where's Austin", Ally, Trish and Dez imagine what their lives would have been like had they never met Austin.
- The Star Trek: The Original Series Fan Sequel Star Trek Continues, has the episode "Fairest of Them All", which is a Sequel Episode to the original Mirror Universe episode, "Mirror, Mirror", except it is set entirely in the Mirror Universe and seen from it denizens' viewpoint, much in the style of Enterprise's "In a Mirror Darkly", right down to using an alternate Title Sequence.
- Ben 10 has an episode, "Gwen 10" where, surprisingly, it's Gwen who gets the omnitrix, not Ben. It's framed by a benevolent narrator explaining how stories can be told different ways.
- The 2003 animated serial spin-off of Doctor Who, Scream of the Shalka, is now considered this as it features a very different version of the Ninth Doctor than the parent series introduced two years later. (The animation was produced before there was any inkling of Doctor Who returning to TV and was in fact intended as a long-term replacement. When the TV revival was announced, all future animations featuring the so-called "Shalka Doctor" were cancelled.)
- Flying Rhino Junior High's final episode, Seeing Double includes an alternate version of the school with punk versions of the main characters and a good guy version of Earl P. Sidebottom aka "The Phanthom".
- Phineas and Ferb did this several times, usually with the characters being born in a different time period. Or in a Galaxy Far Far Away.
- The Powerpuff Girls was to have an alternate reality episode, "Deja View," half of which was supposed to be in CGI, but it went over budget and was facing a tight deadline. The original story outline was given to DC Comics for issue #50 of the PPG comic book. It had the girls sucked into a vortex and winding up in Townsville's alternate counterpart Viletown and the girls' alternate counterparts, the Powerpunk Girls rending Townsville asunder.