Another type of Alternate Universe is that which doesn't take any of the characters, but instead takes concepts, or machines. Such Alternate Universes are uncommon, but exist. Gundam is the perfect example, with no less than seven separate universes, all of them rehashing essentially the same plots and concepts — in particular, the conflict between those living in space and those living on Earth. With giant robots.
Compare with Masquerade, where a world might look the same, but something hidden makes it different.
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In the Kyoto Animation adaptation of Key'sVisual NovelCLANNAD, Tomoyo's arc, which was never completed properly, was showcased in an AU OVA entitled Another World: Tomoyo Arc, where Tomoya never met Nagisa and Tomoyo is the winning girl.
In July 2009, Kyo Ani released the final DVD of Clannad: ~After Story~ that contains an extra OVA episode entitled Another World: Kyou Arc. Kyou finally gets her arc!
And an even darker furure from which Cell hails. He killed his timeline's version of Trunks, who had already killed the Androids Cell needs to absorb, and stole the time machine so he could absorb them in the past.
In the Fullmetal Alchemist anime the opposite side of The Gate is shown to be our universe. The two worlds have vastly different continuities but all humans have an Alternate Self on the other side of the gate.
As it was written by the same mangaka as Rave Master, Fairy Tail had to have one of these as well, in the form of Edolas. It makes for an interesting plot twist, and despite its relative lack of plot significance, it doesn't feel tacked on at all. Although it does explain a good few things, like Happy and Carla's origin, and why Jellal and Mystogan look identical to one another.
The Hetalia Bloodbath 2010 event: the culprits turn out to be alternate versions of various countries from another world where everyone has cat ears and they walk around nude like it's no problem, and apparently contains 123 different Frances. The survival of that world depends on finding a nation with a certain mark on their chest or butt before the end of Christmas, hence the stripping.It Makes Sense in Context.
Steel Ball Run is an Alternate Universe to JoJo's Bizarre Adventure, created in-continuity after Made In Heaven reset the universe.
The Big Bad of that arc had a Stand based around weaponizing a similar concept. He could escape death by pulling an identical version of himself from another universe to replace him, and could also force others to come into contact with their dopplegangers, and thus be obliterated. The other universes are almost identical, with the sole prominent difference being the lack of the Holy Corpse in all but the main universe.
The Kirbyanime is meant to be an alternate universe from the games, something many fans miss.
It's not just the fans—the box art for the GBA Kirby's Adventure remake Kirby: Nightmare in Dreamland inexplicably had a few anime-only characters on it.
A major plot twist in Rave Master involved this trope: the entire series exists within an Alternate Universe, which was created when the last survivor of the original reality manipulated time in order to create a parallel world where The End of the World as We Know It didn't come to pass. The Omnicidal Maniac that was destroying this parallel world was in fact a balancing force created as a result of the unnatural divergence in the timestream.
In the fourth Suzumiya Haruhi novel, The Disappearance of Haruhi Suzumiya, Kyon suddenly finds himself in a world without supernatural powers, with what SOS members remain leading normal, human lives.
It is, however, quite important to the plot that it actually was not an alternate universe, the one he has always been at had been rebuilt.
One fan also seems to make an excellent example with an AU universe comic about TTGL worthy of the series.
Tsubasa Chronicle has many different worlds, and the four protagonists actually come from different worlds.
The Adventures of Luther Arkwright is based on the premise of an infinite multiverse of parallel universes or realities which differ with each other in many things. For example, one of the main places where the action in the comic book takes place is a 20th century world where Great Britain is still ruled by a puritan government and a descendant of Oliver Cromwell. In addition, New York is New Amsterdam and the other great powers are the empires of Russia and Germany.
Even Archie Comics do this sort of thing, a recent, notable example being the Life With Archie series. The storyline where Archie marries Betty is treated as a different universe from where Archie marries Veronica. The former also happens to feature a character traveling between universes!
The 5th Dimension and Qward remained, and in fact, Qward took the place of Earth-3 in establishing a place of origin for the Crime Syndicate.
An early post-Crisis Superman story established that Superboy had existed in an "alternate time loop" created by the Time Trapper simply to explain an inconsistency in the tradition of the original Earth-2.
D.C. began labeling their high-concept imaginary stories "Elseworlds" as if to imply that they took place on alternate Earths.
The 1996 Marvel vs D.C. crossover clearly states that Marvel and D.C. Comics take place on parallel Earths. This is important to the overall plot of the story, though it doesn't seem to have had much impact on the ongoing lives of either line of superheroes.
The 2003 JLA/Avengers also says that Marvel and D.C. are parallel Earths.
The fate of the Superman of Earth-2 was still apparent in the story The Kingdom.
D.C. eventually created Hypertime as essentially a similar device to exploring alternate versions of characters.
And, finally, the very plot of Infinite Crisis made it so the parallel Earths had to have existed.
While a longstanding tradition at DC, the Second Wave of The New 52 had the re-established Earth-2 as a focus. (Not only the Earth 2 comic itself, but also Worlds' Finest, whose stars are refugees from that reality.)
Forever Evil involves the Crime Syndicate of the re-established Earth-3 invading the main Earth.
The Multiversity spotlights six of the other worlds in the new Multiverse: Earth-4, a Watchmen-influenced Charlton world; Earth-5, pretty much the old Earth-S, where the Fawcett characters live; Earth-10, where the Quality characters fight the Justice League in a world where the Nazis won; Earth-16, featuring the children of Superman and Batman; Earth-20, a pulp-styled world with Doc Fate and the Society of Super-Heroes; and Earth-Prime, still intended to be our world.
Another recurring world that's shown up is Earth-23, where the chief differences include the Justice League being black and Superman secretly being President of the USA.
Marvel Comics has explicitly adopted a Multiverse as part of their canon, with "out of continuity" storylines assumed (or explicitly stated) to have happened on an alternate Earth (or alternate-wherever). The "main continuity" of most Marvel titles is labelled as taking place on "Earth-616".
Galactus is the sole known survivor from the previous Big Bang-Big Crunch universe cycle, making him technically a native of an alternate universe.
And then there's the Age of Apocalypse storyline. Although it was initially an alternate present for Marvel's baseline universe "Earth-616", it became an alternate reality when Jean Grey split it off into a separate universe during the events of X-Men Omega.
The comic Exiles explores this idea to its fullest, having the main characters hop between different Marvel AUs and fixing problems.
According to Earth X every time you alter history through time travel you create an alternate universe.
There are four known ones in Paperinik New Adventures. In order of appearance, they are: a universe where the Evronians are the Benevolent Precursors who taught science to the inhabitants of the Americas and the Vikings are the dominant power of Europe that are trying to invade (the recurring character Urk comes from there, and was accidentally pulled in Paperinik's own by the Raider); a The Lord of the Rings-like world conquered by an alternate and dimension-hopping Raider, who rules benevolently after finally ending the incessant wars; the timeline from which the alternate Raider comes from (specifically an Alternate Universe of PK's canon future); the Ultimate Universe Continuity Reboot gets established as one by the original PK showing up in the last issue. The story The Day of the Cold Sun specifically establishes there's an infinite number of universes, but travel between them is almost impossible due the sheer numbers of them (in that story the Raider has a device to travel between them, but after finally succeeding at charging it he gets stuck in all of them at the same time because the device couldn't choose one).
Let's not forget how it's done in Archie's Sonic the Hedgehog, where universes are known as "Zones". Beginning with the Mirror Universe with Scourge the Hedgehog, and continuing with Blaze the Cat and her "Sol Zone". And did I mention, in one "zone", Sonic is a cop who patrols between zones?
The Star Wars Infinities comics. Yavin goes up in smoke? Vader in white armor? Sweeeet....
And Yoda kamikaziing the Death Star into the Imperial Palace on Coruscant.
Tom Strong features Terra Obscura, which is an alternate Earth... but it's not in another dimension or universe. It's located at the opposite end of the galaxy from "our" earth, and is its exact double — it's even part of a replica solar system. Tom theorizes that this is a ghost particle phenomenon on a cosmic scale. What differences there are are fairly minor, with the existence of more plentiful and more powerful science-heroes on Terra Obscura chief among them. Other than that, history went along many of the exact same beats, and thus it's not all that different from what we're familiar with (including its own version of Tom himself, Tom Strange) — though apparently the War of the Roses swung the other way, as New York is instead called "New Lancaster".
It's mentioned off-hand that the first time Tom Strong and Tom Strange met, it was as enemies, which means the Evil Twin angle saw some exploration as well.
Zot!: It is left ambiguous which Earth is the real Earth, but it is hinted that Zot's world is merely our Earth with all the bad parts taken out. It becomes more evident when it is revealed that the year is always 1965.
iSwear, an iCarly fanfic, starts with Carly entering an alternate universe, and every time she loses consciousness she is automatically evicted from one universe and pushed onto another in a manner similar to Quantum Leap and Sliders. The horror kicks in when you find out that other versions of Carly have been doing the same thing and that many have died due to ending up in dangerous Crapsack Worlds.
Just One, Big, Happy Kingdom is a Merlin fanfic in which an eighty-year-old Merlin decides to teach his younger self a lesson by putting him in a mirror universe ("Not-Camelot") and put Not-Merlin in the normal Camelot. It's one of those mirror everybody-is-his-opposite universes.
Mass Effect Clash Of Civilizations: Aside from the obvious (the UNSC in place of the Systems Alliance, the Covenant species existing, the whole Halo side of the crossover), in this universe the Council lifted the ban on opening closed relays several years before the start of the story. In canon Mass Effect, this never happened, and even during the trilogy the law against opening relays was still upheld.
The Odyssey, an Exalted fanfic. It's notable for both its quality and the fact that the point of divergence has not yet become apparent. Something happened to the Fivescore Fellowship, though..
Two of these exist in Phoenixs SSBB Case Files, aptly named Alternate Turnabout and Alternate Turnabout 2. The first has Larry Butz working as a defense attorney, with Adrian Andrews at his side, while 2 features Franziska von Karma and assistant Dick Gumshoe working for the Wright and Co. Law Office.
The Pony POV Series has such a thing. It's explained that all the worlds diverged from the Heart World (implied to be the actual shows' timeline) and are effected by changes there, but can break off and continue on their own in the event the change in the Heart World is so great said universe can no longer harbor the connection. The ones the series itself focuses on are it's main timeline and the Discorded Timeline, a Villain World ruled by Discord, but we also see a lot of alternate timelines which Princess Luna refers to as "possibilities and impossibilities". Applejack gets to see quite a few of them on two seperate occasions, the one that means the most to her being the Orangejack universe, where she never left Manehatten. She eventually gets to meet Orangejack and they team up to fight Nightmare Mirror, Applejack's own Superpowered Evil Side who may or may not be another alternate version of her. It also turns out Orangejack is an Element Of Generosity and there are universes were Applejack was one of the other Elements as well, all of which are summoned to fight Nightmare Mirror. There's also a universe were Rainbow Dash turned into Nightmare Manacle, another where Pinkie Pie turned into Nightmare Granfalloon, and another were the mane cast are the Mighty Morphing Power Ponies fighting a Goldar version of Gilda. Oh and Pinkie Pie is actually the G3.5 Pinkie Pie and is how she is thanks to being left pretty much untouched by a Cosmic Retcon that turned that universe into the G4 universe.
Reality Is Fluid starts out with the USS Bajor being tasked with testing a new sensor array designed to detect and observe alternate universes. Two of the universes detected are an AU where the Federation apparently lost the Dominion War, and the Star Trek Novel Verse (the fic is based in the Star Trek Online timeline).
The Son Of The Emperor mixes the real world with the world of My Little Pony: Friendship Is Magic. This results in an Alternate Universe where the ponies grow to the size of horses and have been used for centuries in warfare, mytical creatures like griffons are commonplace and magic exists.
Streets Of Rage Saga, a 10-story saga based on the Streets of Rage game series (both the canon trilogy and several fan-made games and remakes based on said trilogy), takes place in a setting based on but highly different from the canon. Just a few brief examples, with the canon information in parentheses: Axel lost his father in a fire that was set by the man who would later become The Dragon for the first story's Big Bad (in canon, no mention is made of Axel's family members); Blaze comes from a Doomed Hometown that was razed by The Syndicate (in canon, the only back-story on her is that she was a rookie cop who quit alongside Axel and Adam because of the force's corruption); and Mr. X is a U.S. senator with the full name of George Xetheus (in canon, his real name wasn't divulged and his role as a Corrupt Corporate Executive was only hinted at in canon and expounded on in Bombergames' remake).
The Uplifted series does this, by showing what happens when Humanity is uplifted circa 1942 by the desperate Quarians with the intention of using them to retake Rannoch.
With Strings Attached is set on another planet in an alternate universe. Additionally, the four visit three other universes (including one set in a 1950s New York, more or less); the Fans are watching from their universe; the Dalns gods inhabit yet another universe; and Jeft comes from still another.
This trope is likely to be used by anyIntercontinuity Crossover fanfic in which the melded continuities would otherwise contradict one another.
An ER fanfiction series titled "Dreams That You Dare To Dream" had several of the main characters leaping to alternate universes in which several of the show's major changes never took place—Carol did die from her suicide attempt from the first episode, Susan Lewis never left town and married Mark Greene, etc. Another one set on New Year's Eve 1999, titled "Countdown", took a similar form, though it only focused on the typically unpopular Kerry Weaver.
It's implied that the two Cinderella sequels are set in different universes.
The One is a cross between this and Conservation of Ninjutsu. The villain is traveling around to the various universes killing all the alternate versions of himself so he'll have all the power that would otherwise be spread out between them. Since the hero is one of the alternates, he winds up with bigger and bigger slices of the power pie as well, making for a battle royale when it's down to just the two of them.
Super Mario Bros. The Movie posits a "sub-dimension" created through the impact of the meteorite into earth that caused the extinction of the dinosaurs. The dinosaurs continued to evolve in this sub-dimension in the city of "Dinohattan", a city mirroring New York city.
In Cube 2: Hypercube, the hypercube transects parallel universes. The characters don't realize this until they start running into duplicates of themselves and each other. Exploited by one character who uses them as a human food source.
The Paratime series by H. Beam Piper is based entirely around this concept, in which an advanced Earth civilization with the technology to explore alternate universes does so in order to secretly mine them for resources.
In Teresa Edgerton's Celydonn trilogy, the Inner Celydonn plays this role to Celydonn proper, so that, for example, the version of Tir Gwyngelli known in traveller's tales really exists as the home of The Fair Folk.
The Devil's Alphabet by Daryl Gregory is a novel where a virus of sorts mutates the populations of a couple of cities in different parts of the world. The eventual realization is that the various types of new humans (Argos, Betas and Charlies) are what humans are normally like in alternate versions of the world.
Created by Hex the magic AI as an emergency dumping-ground for a thaumic overload, an orange-sized spherical universe is kept on Rincewind's desk at Discworld's Unseen University. Most of the UU faculty think this narrativium-deprived alternate reality is a silly waste of time; even so, the Archchancellor occasionally (meaning, whenever a new Science of Discworld book is published) tasks his wizards to offset interlopers' tampering with the pocket universe's history. Silly or not, it is University property. "Roundworld" is, of course, our own universe.
Alternate Universe theory crops up elsewhere in Discworld, too, such as in Lords and Ladies, where Ridcully, upon being told that there's a universe somewhere where he married his childhood sweetheart, gets annoyed that he wasn't invited to the wedding:
Ridcully: You'd think I'd think of me, wouldn't you? What a bastard!
In Dragonlance, Raistlin succeeds in becoming a god and killing every other god as well as all life in Krynn. Then Caramon time travels back to prevent him from succeeding.
The Alternate Universe part comes from the suggestion that there are universes where Caramon didn't succeed.
In The Edge, the Weird is a mirror universe to our world, mirrored so that Florida is in the west and California in the east. None of the characters are duplicated, though.
The Man in the High Castle by Philip K. Dick contains an alternate 1960s California controlled by the Japanese after a defeat of the allies during WWII. There is mention of another alternate reality, apparently revealed to an author who writes a book about such an alternate in which the US does not lose WWII. This is slowly revealed not to be "our" alternate, but one dreamed up by the writer, and of no special significance. The book was written using the I-Ching as a guide to the character's actions.
Robert J. Sawyer's trilogy, "Hominids", "Humans", "Hybrids", is all about an alternate universe where Neanderthals didn't go extinct, but homo sapiens did.
The alternate history series 1632 runs on this trope. Not long after the Virginia mining town from 2000 appears in Europe in 1632 during the Thirty Years War, some characters speculate they have moved to a different universe.
In Smoke and Shadows, Arra comes from what seems to be a parallel Earth given how easily she adapts to life in Vancouver. Her world was less technological, but magic use was mainstream.
Spectral Shadows has this; Word of God says that the "Somebody Else's Dream/Episodes from Hell" segment of Serial 11 is this.
The Myriad UniversesStar Trek novella collections have the "for want of a nail" version of this trope. The Mirror Universe short story collections, on the other hand, are very different to the main universe.
In Wildside by Steven Gould, a teenager has a portal to a parallel world in which humans never evolved on his farm, they try to use it to become rich by exploiting it, but the teenager's father came from a different world in which the Industrial Revolution ran amok and destroyed it, eventually using portals to come to our timeline saving the uninhabited world as a potential lifeboat for our world
The Probability Broach by L. Neil Smith — a police officer in a dystopian United States is accidentally blown into an alternate universe where the North American continent is a libertarian society, and must help his alternate self defeat a plot to conquer this new world. Basically an Author Tract (albeit an entertaining one) for libertarianism, it's available online as a graphic novel as well.
Live Action TV
Andromeda did several episodes exploring Alternate Universes in various ways: as a Near Death Experience, and as a result of one character's ability to view potential futures. The most noteworthy was "The Unconquerable Man", which was an entire Clip Show playing out events from the show's history with a different lead character.
These eventually became a running gag on the show, with Anya often mentioning universes she could potentially send people to: the universe of infinite Wednesdays, the universe without shrimp, the universe of nothing but shrimp...
At first, "Superstar" appears to take place in an alternate reality where Jonathan is the eponymous Marty Stu, but it later turns out that he had cast a spell that altered reality itself.
There's also the universe as it was Before Dawn and Post-Dawn.
A mirror universe in Red Dwarf uses the same joke.
The Community episode "Remedial Chaos Theory" features the group rolling a die to choose who will go to the door to get the pizza. Abed warns that this will create 6 (actually 7) alternate universes. Everyone else of course dismisses this, but we the audience get to watch each one unfold. The differences ranges from different characters hooking up, mental break downs occurring, everyone having an awesome night, and everything going to shit.
Dark Shadows may well have brought this trope to television for the first time.
"Inferno", an alternate totalitarian Britain (branching off with the 'defence of the republic act, 1943'), which is in a still greater rush to get free power from tapping the magma of the Earth. It is destroyed, with the Doctor able to just avert the similar events happening a few hours later in his 'home' alternate. Not bad at all.
"Rise of the Cybermen"/"Age of Steel" has the TARDIS fall through a crack in time and land in a universe where the Cybermen were being created on Earth. Mickey explicitly references how common the trope is in comics. This universe crossed over again in "Army of Ghosts"/"Doomsday" and its effects continued to be felt in Torchwood's "Cyberwoman" episode. And in the finale of Series 4 of Doctor Who.
In "Turn Left", Donna Noble has an entire alternate universe built around her, where she never met the Doctor, and he consequently dies after the events of "The Runaway Bride." It does not fare well. In fact, the universe without the Doctor is pretty much a terrible place to be.
The Alternate Universe on Fringe is a world where pockets of time and space become unstable due to Walter's kidnapping of Peter by crossing to the other side.
In the AU, there are many details that differ from the characters' home universe, such as Martin Luther King Jr. being on the American $20 bill and the World Trade Centers still standing and Walter never went insane (and never hard parts of his brain removed), and is now the Secretary of Defense and head of their Fringe team, which takes far more drastic action to combat the far more drastic "Fringe Events" that occur "over there". Also, they're keen to show the presence of zeppelins, just so you know it's an alternate universe.
One of the Christmas Specials from Glee features a world in which Artie never got on a wheelchair. As a result, there's no glee club, and Mr. Schue is an alcoholic and still married to his manipulative wife Terri. Also, Rachel never went to New York to work on Broadway and remained in Lima working as a librarian, Puck and Finn never graduated and remained being Jerk Jocks, Kurt didn't graduate either because, without the support and help of the glee club, he was bullied twice as much, and Quinn, without Artie's help and support, never could recover from the psychological trauma of being stuck on a wheelchair after her car crash and committed suicide.
There's also the episode in which Tina is knocked unconscious and she wakes up in a world where she has traded places with Rachel, that is, Tina is the club's main lead and singer while Rachel has to stay in the back and never gets a solo.
Kamen Rider Dragon Knight uses the concept of alternate universes, accessible through mirrors. The Earth Kamen Riders are chosen because they are genetic doubles of the original Kamen Riders from the alternate universe of Ventara.
Sci-fi series Lexx made this its staple. The first season of the show involved the characters jumping through an inter-universe rift twice, and in the second season once at the beginning, before the entire Light Zone was wiped out in the second Season Finale, forcing the Lexx (and a large amount of particle matter from the zone) to get forced back out into the other universe.
Lois and Clark had an Alternate Universe in which Lois was lost in a jungle and Clark had not made himself into Superman.
This does allow the protagonists to discredit the Big Bad, who tries to expose Superman's secret identity. It's kinda hard to argue that Clark Kent is Superman, when both of them are standing right there.
Season 6 of LOST features an alternate universe where 815 never crashed, and many other details are different. Word of God has it that neither timeline should be called "alternate" or "parallel" as those words imply that one is more real than the other. Flash-sideways has been decided to be the proper term. People in the flash-sideways actually retain memories from the other timeline, with Desmond seemingly able to switch between both willingly. The finale blows the flash-sideways out of the water entirely.
The fourth episode of Misfits has Curtis go back in time to the night he and his girlfriend Sam were busted for drug possession (the reason why he was on community service with the gang). After various failed attempts, Curtis does prevent the bust and him and Sam escape from the police, however it resulted on an Alternate Universe in which he was never on community service, which results in Kelly, Simon and Alisha being murdered by the probation worker, something Curtis had prevented from happening in the pilot.
Episode 2.6: A world in which a man who can manipulate lactose reveals their powers to the world, but later when more people with much more impressive abilities he is regarded as a joke in comparison, resulting on him going psycho and murdering Alisha, Nikki, Kelly and Nathan.
And then there's also that episode of Series 3 in which an old man gains Curtis' ability to travel in time and goes back to Nazi Germany to kill Adolf Hitler. However, he fails, Hitler obtains his phone and uses it to make gigantic technological advances that resulted in the Nazis winning WWII.
Homaged in Mystery Science Theater 3000, "Last of the Wild Horses", where Dr. Forester and TV's Frank get to quip at the movie, and evil Mike and Bots watch on from Deep 13.
"Ace" Rimmer (what a guy!) on Red Dwarf came from an Alternate Universe, and travelled between dimensions. The Red Dwarf crew themselves had previously travelled into an Alternate Universe in the episode "Parallel Universe". Some episodes have featured similar alternate versions of characters and events, but were a result of time travel rather than passing into another Universe (notably "Timeslides" and "Inquisitor").
The books delve into this too. While multiple universes are established in Better Than Life, they really come into play in Last Human and Backwards. Last Human occurs when the crew return from Backwards Earth to the wrong universe and try to track down Lister's other self. In Backwards, Ace Rimmer is given a backstory behind Project: Wildfire and turns up to save the crew. Bonus points for the fact that both books, having each been written by Grant and Naylor separately, take place in alternate universes to each other.
In Seinfeld episode #137 "The Bizarro Jerry", Elaine is in a similar social circle where the Kramer equivalent is neat, George's is responsible, etc.
The series Sliders used this as its central premise.
Smallville had an interesting subversion: Clark wakes up in a mental asylum; apparently, he started having delusions of superdom in high school, and his "saving" of Lex in the first episode actually cost Lex his legs. Oh, and Chloe is a freaking nutcase. Of course, it was all a delusion caused by an escaped Phantom that attacked him in his barn and invaded his mind. John Jones (the Martian Manhunter) helped him escape by entering the illusion (as another inmate), and capturing the creature in a Kryptonian crystal.
Season 10 had an Alternate Universe as a major plot line: Clark discovers a kryptonian artifact called a "mirror box" and when activated it takes him to a world where the Kents never adopted him, but instead was raised by Lionel Luthor and goes by the name "Clark Luthor". Clark Luthor himself is brought to Clark Kent's world and causes no end of trouble before the original Clark manages to switch them back. Then it turns out the alternate Lionel managed to come through to the main world with Clark, taking the place of the original Lionel (who was dead) with a story that he'd faked his death. Then Clark Luthor uses his mirror box to come back and send our Clark to his world, where he helps the alternate Jonathan reconnect with Martha, and convinces Clark Luthor to try and use his powers for good, rather than live in Lionel's shadow.
Stargate SG-1 has had many different alternate universes. Oftentimes, the "alternate" Samantha Carter is not in the military and is engaged/married to the "alternate" Jack O'Neill. Alternately Daniel Jackson was never part of the Stargate Program. More often or not, when this is used, Earth is under imminent Goa'uld attack.
Atlantis also does this, though the details vary, and the universes aren't usually quite the Crapsack World versions that SG-1 is fond of.
In the one in the episode McKay and Mrs. Miller, Rodney is a really nice guy with lots of friends and Sheppard is a member of Mensa, greatly annoying everyone with his egoism. In our universe, Rodney is the egoist one, Sheppard is a nice guy who took a Mensa test but turned down the offer to join.
And another is shown in the penultimate episode Vegas. There, Sheppard is a homicide detective with massive gambling debts. He couldn't be included in the team because the stunt he pulled off in Afghanistan got him dishonorably discharged instead of getting Reassigned to Antarctica in time for the pilot. Rodney is more likeable (though one scene suggests that he's simply better at keeping a lid on his ego) and the Wraith already made an attempt at culling Earth just to be repelled by the control chair in Area 51. Oh, and Todd got so delirious from starvation he's speaking in rhymes.
The Rodney from Vegas also mentioned that he once traveled to yet another universe and met an alternate Sheppard who was similar to the main Sheppard.
And the mirror universe provided the means for arguably the best episode of Enterprise. Hooray for mirror Hoshi!!
Star Trek: Voyager didn't make use of the Mirror Universe, but in "Living Witness", a historian hundreds of years in Voyager's future has created a "historically accurate" holo-program depicting the crew as murderous thugs who started a war on his planet. It's up to the Emergency Medical Hologram (the only surviving witness) to put things right... which isn't easy, as he's being portrayed as a Mad Doctor. Star Trek: The Next Generation also didn't have the mirror universe, although it did have alternate universe stories (as the term "mirror universe" in Star Trek refers specifically to that featured in The Original Series and Deep Space Nine).
A slightly different take on this was done in "Author Author" in Star Trek: Voyager, in which the Doctor created a holodeck program peopled by altered versions of the Voyager crew.
it's a different Mirrorverse than the DS9} version, though, where the Empire survives into the TNG era. In it, Picard is a thug, Riker is The Starscream, Data doesn't exist, since Soong was killed, Worf is a slave (and fulfills the Spock role as the only decent being), Geordi is a nasty SOB, Beverly is a brokencaptain's woman, Troi is a mind rapist, and Wesley is out to kill Picard for killing his father.
An Alternate Universe seems to be seen in the Supernatural episode "What Is And What Should Never Be", but it's really all in Dean's head and everything is his perception — Mary's perfect, Sam and Dean are a bit wussy and the family is like any other. In his fantasy, his mother Mary and Sam's girlfriend Jessica were never killed by Azazel, so the Winchester family live perfectly normal lives and his Dad died peacefully. As Dean is utterly unhappy there, it seems he wants a extremely codependent relationship with Sam and the wracking memories of his family.
A real Alternate Universe, or rather a series of them, pops up in the episode "Mystery Spot" thanks to a repeating time loop in which Dean keeps dying. The iteration before the final time loop lasts months instead of the standard day, resulting in a dark, isolated Sam.
Later in the episode "It's a Terrible Life", where Dean is a Marketing Director for a firm and Sam is a techie in the same building with no memory of their hunter life beforehand apart from a few dreams, it's revealed that this was all a ruse from an angel to show Dean hunting is in his blood and he will always find a way to be a hunter. This is also a play on the Wonderful Life trope.
The second AU episode took place in the sixth season, where the brothers are sent to a universe note which is basically our world with a bit of hyperbole where Supernatural is just a TV show filmed in Canada, in which Sam and Dean are played by Jared Padalecki and Jensen Ackles, and there is no magic, demons, angels, monsters, or any supernatural beings at all.
And then there's "My Heart Will Go On", in which the Titanic never sank, somehow causing the Winchesters to own a Mustang, Bobby and Ellen to be married, and Celine Dion to be a lounge singer in Quebec.
VR.5's Missing Episode, "Parallel Lives" had Duncan wake up one morning to find himself in a universe where Sydney, rather than her sister, had died in a car crash years earlier (of course, it eventually turned out that neither sister had actually died; both the car crash and the parallel universe were complex VR hoaxes. The episode was intended to test the viability of replacing the central character for the second season, a possibility which became moot when the series was not renewed).
Wizards of Waverly Place had an episode where Alex goes through a mirror and enters a parallel universe where nearly everything is about her and in her favor.
Xena: Warrior Princess, Hercules: The Legendary Journeys use a mostly standard Mirror Universe: Good characters become Evil, shaven characters become bearded etc. But regular Iolaus is a good, shaven, competent warrior and regular Joxer is good, shaven and incompetent; in the Mirror-verse, they are both good and shaven, but Iolaus is incompetent and Joxer is competent.
There are some weird rules for the two universes. If a person (or a god) dies in one universe, he also dies in the other. Unless they happen to be not in their universe at the moment. This happened to the alternate Iolaus who was trapped in an "in-between" world when "our" Iolaus took a knife in the gut. Also happened to Hercules, as his double the Sovereign was killed while in this "in-between" world.
BIONICLE has the Olmak, also called the Mask of Dimensional Gates. Does exactly that. Its wearer, Brutaka, has used it both to teleport and to send enemies to a dimension they probably won't return from. He tried to send his former friend Axonn into the Zone of Darkness (a pitch-black dimension with only flat, featureless plain with gravity), and also used his (then damaged) mask to teleport Takanuva to Karda Nui to warn the heroes of a great danger. However, the mask malfunctioned, and sent Takanuva into both Alternate History and a Bizarro Universe. After finally finding the another Olmak in one of those universes, Takanuva entered inter-dimensional space and got to his intended destination. This is a Multiverse with a twist, as "our" dimension is explicitly called "the real universe", the rest are only pocket dimensions that shows how things would've turned out if they were done differently. Brutaka's mask was destroyed eventually, but the lunatic villain Vezon managed to get his hands on another one... and it ended up fusing to his face. Now he is a living dimensional gate, and has already visited several other universes (among them a few of those that Takanuva got lost in).
The SCP Foundation has many contained objects that apparently come from (or are doorways to) other universes, many of which are similar to the Foundation's universe.
SCP-2069 ("AEGIS") is a collection of debris that was blasted into the Foundation's universe. It was the aftermath of when AEGIS (a team up between the Foundation and the Global Occult Coalition) used a doomsday device called NOVA as a last-ditch attempt to stop an Alien Invasion.
SCP-2332 ("Thought Messenger") is a butterfly made of ultraviolet light that was originally created and sent out by another universe's version of the Foundation. It ended up in this universe by accident.
The two Dungeons & Dragons campaign settings of Greyhawk and Mystara are both alternate universes to Earth and each other, though this is rarely referenced in game materials and comes mostly from Word of God.
Greyhawk exists in a Multiverse (along with Dragonlance and the Forgotten Realms), but it's not made up of alternate universes. Rather, it's the term used for the system of heavens and hells, elemental planes, the Astral Plane, and so on; the different campaign settings are planets in the same universe.
The entry for 1357 DR in The Grand History of the Realms notes that in that year, on an alternate Material Plane world known as Earth, Ed of the Greenwood gathered together various books and maps given to him by Elminster of Shadowdale, and made the first publication of the Forgotten Realms campaign setting.
Mystara somehow exists in a different multiversal set-up from the other campaign settings. In addition to Earth, it also crossed over with another universe with futuristic technology; a starship from that universe crashed on Mystara and its radioactive engine became a major source of arcane power.
The point here is that, unlike most other official Dungeons & Dragons settings, Mystara and Greyhawk share background elements pulled from early games (such as the aforementioned starship crash, the Barony of Blackmoor, and connections to Earth), but in slightly different formats.
Gothic Earth, a spinoff of the Ravenloft product line, is an Alternate Universe version of our own planet in which supernatural horrors lurk beneath the facade of Victorian-era society. Also, some characters from classic fiction in our world are real there.
Urban Arcana's worlds on the other side of Shadow could be this, but the nature of Shadow makes travel between universes... tricky. As in, 'you can't go back'. One of the adventures includes a character from the other side that have figured out how you can travel between the Earth of UA and his world. This character, and his organization, also appeared in Planescape...
The enemy timeline in Infinite Worlds is Centrum, a scientific state that wants what is best for all, and for this to continue (discovering where this one branched off is a surprise)... others in the Alternate Worlds books have included Gernsback (named for the Golden Age SF editor), where Nikola Tesla's inventions shaped the development of science; Excalli, where the dominant empire is an Aztec-derived one; Roma Aeterna, where the Empire of Rome simply carried on, with the adoption of science; an alternate where China continued to trade overseas; and several versions of the usual "Nazis triumphant" parallel. Oh, and the United States of Lizardia, where dinosaurs evolved into sentient beings but somehow ended up recapitulating human history along the way.
Wizards of the Coast long ago published a set of generic supplements for handling deities in roleplaying games, called The Primal Order. One of the books in this series, Chessboards, covered in exquisite detail how to design and manage an entire multiverse complete with cosmology.
TORG features several different dimensions/realities, each corresponding to a different genre (such as Aysle, a traditional world of Medieval European Fantasy; the Cyberpapacy, a Cyber Punk world run by a Corrupt Church; the Space Opera-influenced dimension of the Space Gods; Orrorsh, a Lovecraftian Cosmic Horror Story in a Heart of Darkness style British colonial jungle setting; the Nile Empire, a world of Pulp Action Adventure; the Living Land, with sentient dinosaurs; and others), all cooperating to invade Earth.
Part of what made TORG such an interesting game is that it was based on distinctly different rules for how reality worked, depending on the context of the home dimension. The Nile Empire, for example, had no room for moral ambiguities: every character was either Good or Evil, though they could change from one to the other under the right circumstances. Characters could engage in literal 'reality duels' with opponents from different dimensions, and the High Lords could do the same with entire areas of real estate.
This trope is a common excuse for game masters to use, when importing player characters from one tabletop role-playing campaign to another.
The Tyranny of King Washington downloadable content for Assassin's Creed III features the player character waking up in an alternate universe in which his mother is still alive, he never joined the Assassins, and George Washington went mad with power after acquiring some Lost Technology and declared himself King of America. In addition to the alternate historical elements, there are some supernatural powers present as well, truly separating the setting of Tyranny from the main Assassin's Creed setting, which is Like Reality Unless Noted.
Makoto's Story "Slight Hope" in BlazBlue: Continuum Shift has her accidentally travelled to an alternate history world whereby Noel wasn't alive and it took place 3 days prior to her own timeline. Rachel ultimately explained this to Makoto and guided her back to her own timeline. Even in Litchi's story, she could sense an alternate universe happening.
Chrono Cross had alternate universes replacing time travel as the main hook.
The original Crazy Taxi has "Another Day" mode. Where in the normal mode most customers want to travel in a certain direction which leads to the cabbie going in a counter-clockwise direction around the circuit, in "Another Day", the customers usually want to travel to a destination in the opposite direction, causing the cabbie to go in a clockwise direction around the circuit.
The DLC for Dragon Age: Origins entitled The Darkspawn Chronicles pitches the idea of a world where The Hero died near the beginning of the game, thus leaving Alistair to save the day. It does not end well.
The areas Yaschas Massif and Academia in Final Fantasy XIII-2 have alternate versions that appear after solving paradoxes in the timeline, and are marked with an X in the year name (ex. 01X AF). You can still go back to the original universe, though.
In the second installment of the "Timeline" mod trilogy for Half-Life, Gordon Freeman is transported to a parallel Earth where the US never rebelled (the major superpowers are the British Empire, the Soviets and the Japanese), and an ice age began some 300 years earlier, threatening human survival. That world's Gordon Freeman has failed, so our world's equivalent is sent to stop the Xen invasion there (as well as an invasion of time-travelling Nazis from our dimension).
Infinite Crisis the video game is set in the DC multiverse, with characters from six Earths colliding:
Nearly every character from Kingdom Hearts is an alternate version of his/her Disney or Final Fantasy counterpart (otherwise the game would run into some serious continuity problems). This is implicitly stated in Space Paranoids.
Technically, Auron might be an exception to this, as he did die and pass on to the afterlife in Final Fantasy X only for Hades to bring him back from the dead to complete a task. He even expressed his former role as a guardian to Sora. The statue containing his free will also echoed his memories from the events of Final Fantasy X.
Kirby and the Amazing Mirror takes place in another literal mirror universe (akin to the Charmed and Red Dwarf ones above), parallel to Dreamland and containing mirror versions of Meta Knight and Kirby.
The Legend of Zelda has plenty of alternate universes to choose from. Due to the timeline shenanigans of The Legend of Zelda: Ocarina of Time, there are at least three alternate versions of Hyrule: One where Ganondorf was stopped before he could claim the Triforce, one where Ganondorf did claim the Triforce (and was stopped by Link), and one where Ganondorf defeated Link. There are also many "realms" such as the Sacred Realm, where the Triforce is usually kept (although at some points it was known as the Dark World.) There is also a Twilight Realm, the world that the Minish come from, Lorule and others.
Based on what has thus far been fan-translated of Magical Girl Lyrical Nanoha A's: The Battle of Aces, it takes place in an alternate universe where Reinforce I/Eins survives and the corrupted Book of Darkness creates "Dark Pieces" of selected cast members (sorry, Arf and Yuuno) to get its own back again.
The Mega Man series has two universes: the main one (Classic, X, Zero, ZX and Legends), and the alternate one (Battle Network and Star Force). The difference between these two timelines is that the latter has internet technology prosper instead of robotics (as was the case in the former).
In a strange way, the alternate universe also rewrites most of the robot masters who were Mega Man's enemies into potential allies, the most notable being Guts Man and Search Man, both whom are enemies in the mainline series, but consistent allies in the alternate timeline.
Pokémon Black and White establishes the reason for having One Game for the Price of Two as because of this trope- the other version is in fact a parallel universe to the one you're playing, and the histories of a few areas and characters are different. Using the Entralink you can visit the other world and see the changes.
The plot of the Portal 2 PeTI DLC involves this. Earth-Prime's version of Aperture is nearly broke, so they decided to cut test chamber construction costs by sneaking the designs into alternate versions of Aperture, letting them build it, then stealing them back. You can either play the part of a test chamber designer with the new level editor, or a test subject traveling between universes to test the new chambers. You end up running into various versions of Cave Johnson, all of whom are still running tests (and probably pulling the same scheme) and crazy to some extent (save for the one who stopped the resonance cascade experiments after buying Black Mesa).
Amongst the other notable universes you encounter are a universe ruled by giant mantis-men, a universe ruled by an evil, sentient cloud god, a universe where Cave Johnson created Robo-Cop, a universe made of money, and a universe with an evil version of Johnson where asparagus is the primary food source of the planet.
The Resistance games take place in a setting where after World War I Germany's economy wasn't totally devastated, therefore Adolf Hitler never rises to power and there was no World War II. Instead, creatures known as Chimera take over the entirety of Europe and by the sequel have wiped out the US.
The Dawn of Victory mod for Sins of a Solar Empire has its premise based on an Alternate History where the course of World War II is changed by the arrival of a powerful alien race known as the Scinfaxi (inspired by Harry Turtledove's Worldwar series). After losing much territory to the invaders, the main world powers manage to develop nuclear weapons and beat them back to the Southern Hemisphere. They then rebuild and consolidate their power. Eventually, the Northern Hemisphere is divided between the Soviet Union, the Greater German Reich, and the Democratic Federation. They manage to develop interstellar flight and settle other worlds. After the Scinfaxi resume their advance, the human powers evacuate the remaining population from Earth and nuke the entire planet from orbit. Fast-forward a few centuries. The three main human nations (as well as many smaller states) are spread out over many star systems and vying for domination. Meanwhile, the Scinfaxi (a vast interstellar empire) are preparing to strike again.
The two Sonic Rush games feature a parallel universe. The first game takes place in Sonic's universe, which is slowly merging with Blaze's. The second game takes place in Blaze's universe... which is apparently a giant ocean.
The Super Robot Wars games are set in an Alternate universes for each of the series portrayed in it(the alternate, of course, being that they're all happening at the same time in the same place). Each game or series is, additionally, an alternate universe from each other. Then there is the Original Generation universe, which contains all the original characters and mecha from the other games and then some, which also has its own Mirror Universe, the Shadow-Mirror universe, which is itself the Original Generation version of the Shadow-Mirror universe from Super Robot Wars Advance. Confused yet? We haven't even gotten to the Endless Frontier!
In Tales of Xillia 2, much of the plot revolves around the exploration and destruction of alternate universes, which are threatening the original universe simply by existing.
The Medieval II: Total War conversion mod Thera is a funny example. Thera vaguely resembles high-medieval Earth as far as climate, positions of civilizations and the cultural, technological and historical themes of said civilizations are concerned. Several real-world religions such as Christianity, Islam and Norse Mythology are present as well. That said, the world has a radically different history, and the landmasses are different. Also, there are a number of Low Fantasy elements present, especially in Version 4 of the mod: velociraptor-riding Paynal cavalry, a playable faction being a dead-ringer for Isengard, hostile tribes of frost giants roaming around the northernmost continent, and various Public Domain Artifacts such as Excalibur, the Holy Grail and the Book of Morrigan being real and possessing magical power.
And, mind-bogglingly, despite what the game says, it actually has some bearing on the main plot. Joshua flees to that universe after shielding Neku from Minamimoto's Lv. i Flare. Whereupon he challenges Another Day!Neku to a Boss Rush to kill time.
It also seems to cross over into The Multiverse with certain people as they can go to other dimensions, and even meet themselves if they aren't careful.
Dangan Ronpa has a "What if?" version where Naegi finds a switch to escape the school before any of the students can attempt a murder.
The main plot behind Little Busters! can be described as this. At first you don't realize because you're playing like any other DSIM, but at each playthrough the two main characters evolve a little (better seen on their status screens) and little things change from one playthrough to the other. It's only when you complete the Rin route for the second time, after playing through all the other five routes that it's revealed that the world they live in is actually an alternate universe created for the two main characters by the other eight, in order to help them cope with what happened in the real world.
The When They Cry-franchise is filled of this, refered to as fragments/kakera. In Higurashi the Ground Hog Day is revealed not to be repeats of the same events but instead different universes with a certain person pushing the Reset Button after each arc searching for a fragment in the sea of fragments where Rika won't be killed. In Umineko we are introduced to witches who can travel in the sea of fragments looking for specific events that fit their needs or wants.
The 150th Strong Bad Email had Strong Bad visiting many of the website's alternate universes.
In The Adventures of Dr. McNinja The universe the setting is in is sandwiched between two other realities, the Radical land, and what amounts to the real world. These universes both bleed their coolness and lameness into the comics one respectively so that its cooler than our universe but not as cool as the radical lands.
Bittersweet Candy Bowl, According to the commentary, the chapter "Another Path" was originally intended to be set in an alternate universe where Paulo had sex with Lucy during her Mental Breakdown in "Another Shoulder". The final version has it as a daydream of Paulo's.
Bob and George has an infinite number of them, and Bob visits quite a few. The title characters themselves are from a different universe than the one where most of the action takes place.
In Bobwhite, Cleo freaks out over the many-worlds hypothesis and its implications on fast food. In this universe, she never orders burritos because they're gross... which means that in some other universe she always orders burritos. But why?
There are a few of these in Breakpoint City, though they haven't played a major part so far.
Dinosaur Comics has an alternate universe where everyone has goatees, a Shout-Out to the Star Trek episode "Mirror Mirror," in which the Spock counterpart wore a goatee. Anytime you see an alternate universe counterpart with a goatee, chances are it's a Shout-Out to "Mirror Mirror."
Dumbing of Age is an alternate universe to Shortpacked! and the other series in Dave Willis' Walkyverse. It reboots the story by placing it back in college (most of the Walky cast graduated from college in 2001) removing the science fiction elements completely, and using a Sliding Timescale so the characters will never graduate. Shortpacked is still running alongside it, though, ensuring the walkyverse will continue.
In Dragon City, Erin's friend Natasha reveals herself to an alternate universe counterpart despite Erin having blue scales and Natasha having brown.
Actually, as Natasha (the brown Erin) points out, due to genetics, Erin was more likely to be brown than blue and that the blue Erin is a genetic fluke.
Yes, Erin IS that vain to have made friends with her other world counterpart.
In El Goonish Shive, the Word of God said that at least four dimensions have meddled with the "main" one. Most of them are Alternate Universes, each with its own version of Tedd or other main characters.
Fall City Blues revolves around two versions of the same person forced to live together when their alternate universes were merged to save space.
Alternate Universes play a big role in the 'Maze of Many' arc in Goblins; the Maze itself is a Pocket Dimension which allows different iterations of characters from across multiple realities to exist in the same place simultaneously.
In Homestuck, initiating the Scratch creates one of these by resetting the conditions of the game, including the players and their universe. As a result, the players of the initial session switch places with their ectobiological parents, and vice-versa. This has happened twice so far: once to Earth, and once to Alternia.
Jix had a story that took place in an alternate reality where Remula had taken over the Earth and it was discovered later that the original Lauren had actually be transported to that universe when she caught up to her counterpart.
If they can be successfully opened, Panegates in The Mansion of E allow access to alternate universes.
MS Paint Masterpieces has a number of alternate timelines that are shown as side-stories. As X explains in filler, there's only one actual timeline, and when you mess with time travel, you destroy the projected one, which is what Wily's up to between the first and second games.
The protagonists of Paonia Pawns gain the ability to travel between these; in many, some sort of disaster has wrecked the local civilization.
A sci-fi dimension heavy on tropes from Star Trek and Alien,
A "Dimension of Pain" inhabited by demons,
A rather saccharine dimension where everyone is always nice and friendly to each other, there's no beer, and the main source of food is rice cakes,
A dimension where everyone has purple hair and speaks Portuguese,
An anime-parody dimension where battles between good and evil were regularly fought out by giant robots, in which the entire universe is actually a power source for a giant waffle iron (don't ask),
A dimension that has been invaded by Aylee's race, and
A dimension that has been overrun by mutants, with the only survivors holed up in the Orwellian 4U City, which keeps its inhabitants drugged into submission.
John Ringo's Hell's Faire features several Sluggy Freelance strips as if they were created within the novel's setting. This was possibly a favor in return for the shout outs to Sluggy Freelance in the third and fourth books of the series.
Supernormal Step takes place on an AU Earth with magic and fantasy creatures. It is one of many dimensions, and two of the main characters are actually from our normal, boring one.
In What Birds Know, a mysterious tower acts as a gateway between the normal world and a bizarre version where people lay eggs, among other oddities.
Dragon Ball Multiverse: In total there are 20, each going down a different path in DBZ history (Goku becoming evil, the Namekians fusing to form a Super-Namekian, etc).
Fate Nuovo Guerra takes one of Fate/stay night's bad endings and runs with it as their Back Story. The Fifth Grail War results in the destruction of Fuyuki City, prompting the Einzberns to start a new Grail War elsewhere.
In Lords of creation every one of the new gods became that way by successfully offing a god in their own universe, now they have to create their own and hopefully not screw it up.
Phaeton takes place entirely in and out of alternate universe (Labeled Alpha Gamma 64) and the records of events were somehow sent to our universe, exactly how is as of yet untold.
Survival of the Fittest has had several small-scale AU RPs. These range from simple 'What-If' scenarios (What If the students had been rescued on Day 3, What If SOTF really was a TV show, etc) to radically different concepts such as MechSOTF and SOTF with zombies.
Fairly recently, a spin-off site effectively dedicated to Alternate Universe versions of Survival of the Fittest was created, with the pilot in an interesting Continuity Nod, being an alternate version of Battle Royale, the concept which SotF was based off.
The Mini site also now hosts SOTF: Evolution, which is like normal SOTF, only with 20 characters instead of the Loads and Loads of Characters the main site has, and with Super Serum induced mutations instead of designated weapons.
Tasakeru takes place in an alternate universe where humans have never existed.
A popular fad on YTMND is to take pre-existing memes and create Alternate Universe counterparts, usually under the PTKFGS moniker ("Punch The Keys, For God's Sake!", another one of Sean Connery's lines from the famous scene in Finding Forrester that named the website), although even more Alternate Universe versions exist, usually as either "Yes Yes" or the elusive "Fourth Corner", where no-one can really agree on a final name for the latter.
In the season four finale of Adventure Time, the Bigger Badthe Lich finds and opens a portal to The Multiverse. When Finn and Jake follow, we see them in a universe where the Mushroom War never happened. Thus, the Candy Kingdom doesn't exist, Jake can't talk, and Finn is not the last human. He also has a robot arm.
We find out more about this in the season 5 premiere. Finn wished the Lich out of existence, so he and Jake ended up in an alternate timeline where the Ice King performed a Heroic Sacrifice to prevent the final bomb from falling in the Mushroom War, and the creation of the Lich, from ever happening.
In the Codename: Kids Next Door episode "Operation: P.O.O.L." Numbah Four travelled to an alternate world where the KND were the DNK (Destructively Nefarious Kids). His own evil counterpart was the leader (complete with goatee).
"Life, the Negaverse, and Everything" in Darkwing Duck — a mirror universe set up to explain the origin of Negaduck (not to be confused with the self-proclaimed Negaduck whom Megavolt accidentally created in another episode by dividing Darkwing into good and evil clones) The portal to the Negaverse was lost at the end of this episode, in a traditional Status Quo Is God ending.
In "The Farnsworth Parabox", Farnsworth creates a box leading to an alternate universe where every coin toss has the opposite outcome. There are also lots of other boxes, leading to other alternate universes, each linking to each other.
In "I Dated A Robot", Fry goes to the edge of the universe and sees alternate versions of himself and his friends, all wearing cowboy hats.
In "The Beast With A Billion Backs", a portal opens to an alternate universe, home to only one sentient being: Yivo, the infinitely huge, love-lorn ball of tentacles.
In "The Late Phillip J. Fry", after Farnsworth, Bender, and Fry have reached the end of the universe, a second Big Bang creates a universe identical to the last, giving the trio a chance to go home. And giving Farnsworth a chance to shoot Hitler. And once they reach their time, Farnsworth accidentally slips on the controls, forcing them to go all the way back around again. This time around, Farnsworth misses Hitler and hits Eleanor Roosevelt instead.
In "The Lesser of Two Evils", the sign which says "Tonight: MISS UNIVERSE PAGEANT" a moment later turns into "Tomorrow: MISS PARALLEL UNIVERSE PAGEANT".
In "That's Lobstertainment!", there is a Parallel Universal Studios side-by-side with the Universal Studios.
An episode of G.I. Joe featured a timeline where Cobra had succeeded in taking over the world.
Justice League had several — the retro-styled world of the Justice Guild, the dark dystopia of the Justice Lords, the Vandal Savage-ruled world created through time travel, and others.
Notably, the Justice Lords Universe depicted Arkham Asylum, and Gotham City for that matter, as very bright, Metropolis-esque places, in one of the few instances of the city being shown during the day.
The goatees are a Shout-Out to the Star Trek episode "Mirror Mirror," in which the Spock counterpart wore a goatee. The eyepatches are from the Doctor Who episode "Inferno," in which the fascist counterpart to one of the recurring characters wore an eyepatch.