Alternate Reality Episode
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).
- "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.)
- The Last Dragon Chronicles: Fire World.
- Fire Ascending goes through quite a few.
- The entire premise of Sliders.
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.
- 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".
- 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.
- 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 is a racist police officer 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.
- 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.
- 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 acccidently 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.
- 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.
- 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.
- The Stargate Atlantis Season 5 episode "Vegas" 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.
- 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.
- Bones did one in which 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.
- 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.
- The Doctor Who episode "Turn Left" is created when time-line interference makes a universe where the companion Donna Noble never met the Doctor, and as a result, he died. A space-ship attack at Christmas meant that Donna lost her job, although she did win a prize out of town the next holiday season. Good thing, too, because without the Doctor there to help London was nuked and everyone in the city died. 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.
- 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.
- 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.
- 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 Piece gets shot in the leg and dies, the apartment catches fire, Troy eats a flaming troll doll and loses the ability to speak, Jeff looses his arm, Shirley succumbs to alcoholism and Annie gets committed to a mental institution. Abed dubs this "The Darkest Time-Line" and makes everybody fake beards.
- On season 7 of The Big Bang Theory in the episode "The Hesitation Ramification," the main characters explore the ways that Sheldon has changed their lives through a series of "What if" clips.
- 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.
- 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.
- 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.
- The Fairly OddParents have done this a few times. Examples include the episode Timmy wished everyone was part of an action movie, with Timmy as the buff hero, Jorgon as the villain etc. and The Big Superhero Wish where everyone in town becomes either a comic book hero or villain.
- 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.