Protagonists who need to SaveTheWorld in AnotherDimension often find [[RisingComplications their original dimension endangered as well]].

Maybe you're TrappedInAnotherWorld, fighting monsters and saving people so you can find your way home... and then you ''do''. Or maybe you've gone to another world after adventuring around your home, and found something a little too familiar about this place. Maybe you even go between worlds on a regular basis, and things are getting serious on the other side.

Either way, you discover the two worlds you've been flitting about in have a strange connection. It doesn't matter what it is, but it let you into the other world, and it can let something else out into yours. Generally it's monsters roaming the streets, but there can be other effects. If the more mystical of the worlds is based in a computer realm, expect [[EverythingIsOnline a deadly effect on your hometown hospitals and roads]].

The other world's still in danger, but now so is ''yours'', and the {{Muggles}} certainly can't do anything about it. What do you do? You grab your adventuring party and a couple of friends from your homeworld, and you go out to SaveBothWorlds.

Contrast with UpTheRealRabbitHole, where both worlds are in jeopardy but the heroes don't see the one that isn't their own as real enough to merit saving. May overlap with TheCallKnowsWhereYouLive.

----
[[foldercontrol]]

[[folder:Anime & Manga]]
* ''Franchise/{{Digimon}}'':
** Anime/DigimonTamers would've just been "save Earth", but the BigBad was directly tied into both worlds, and could only be defeated from Earth with help from both sides.
** ''Anime/DigimonFrontier'' flirted with the idea an attack on the real world in the penultimate episode's cliffhanger, but the BigBad never actually made it there.
* In [[Anime/FullmetalAlchemist the 2003 anime version]] of ''Manga/FullmetalAlchemist'', alchemist technology making it into our world is the plot of TheMovie.
%%* 'DragonDrive' - A video game leads to a virtual world that acts as a stepping stone to an alternate world. With Dragons.
* It turns out that ThoseWhoHuntElves need to get back to their home dimension to prevent it from fatally merging with the one they've found themselves stuck in. So their quest to get sent back becomes all the more important.
* In ''Manga/{{MAR}}'', Ginta's world and MÄR Heaven are connected largely by Snow's existence as a clone created from a fragment of Koyuki's soul. The Orb is also the manifestation of all the evil in Ginta's world as well. His plan was to use the connection between Snow and Koyuki to rip open a giant portal between the worlds to conquer Earth as well. In the end, Ginta ends up saving both worlds and Snow and Koyuki merge into a single person. Note this is only in the anime, in the manga the connection is different and the Orb's plan... doesn't make a whole lot of sense.
%%* ''{{Paprika}}'' has the protagonists trying to save both the real world and the DreamLand.
* ''PlanetLadder'' features a girl who discovers that there are nine dimensional Earths engaged in war and are moving towards collision with each other. She is [[SelfFulfillingProphecy prophesied]] to be the "Girl of Anansi" who can save only one of these worlds, but journeys among all the worlds to search for a way to save them all.
* ''SonicX'': Towards the end of the second series, the two worlds are revealed to be merging into each other again, with the catastrophic effect of canceling out each others timelines and causing time to come to a stand still. [[spoiler: The only solution is to send the Sonic characters home.]]
* ''Manga/WatashiNoMessiahsama'' starts off with TrappedInAnotherWorld, with occasional visits back home. Then [[spoiler:monsters appear on Earth, and eventually Earth is threatened with destruction. Naturally, our heroes can't save just one of the worlds]].
* PrettyCure has this in every series.
[[/folder]]

[[folder:Fan Fic]]
* ''FanFic/TheCaptainOfTheVirtualConsole'' has this as its plot. Gancena must save the video game worlds and her own.
[[/folder]]

[[folder:Films]]
* The second half of ''Film/LastActionHero'' has Danny returning to the real world and bringing fictional action movie hero Jack Slater with him. Unfortunately, [[spoiler:Benedict is there as well, and he's got the ticket to travel between movies and the real world to bring through anything he wants.]]
* Sort of done in ''Film/MirrorMask''. By saving the dreamworld, Helena also saves, symbolically, at the very least, her mother's life, and stops "her world" from being shattered. It's not as {{Narm}}y as it sounds.
[[/folder]]

[[folder:Literature]]
* Technically, the titular heroine from ''May Bird'' series has to save "only" the ''Ever After'' world, but since all humans (including herself) will inevitably go there after death, this affect everybody on Earth as well. Not to mention that [[spoiler: the BigBad is actively interfering with Earth, too, and it's only a question of time when he wrecks the Earth directly.]]
* ''[[{{Narnia}} The Magician's Nephew]]'', when Diggory lets Jadis loose in London and then in Narnia.
%%* ''Literature/HisDarkMaterials'', not just worlds that Will and Lyra come from, but the entire multiverse.
%%* The ''Literature/ApprenticeAdept'' series; Stile is a native of science-based Photon, but is brought to magical Phaze as part of a GambitRoulette to correct an imbalance that would destroy both worlds.
%%* AaronAllston's ''DocSidhe'' and ''Sidhe-Devil'' both fight foes that could disturb both "the grim world" (ours) and "the fair world" (Faerie).
* In the ''{{Everworld}}'' books, it would be a bad thing if the gods crossed over into the world of our own, or if aggressive human men with guns crossed over into the world of Everworld. Both of these dangers threaten to happen over the course of the stories.
%%* ''KeysToTheKingdom'', particularly since if the House falls, so does the rest of the Universe.
* Mark Anthony's ''Literature/TheLastRune'' series, which features characters spending time in, and crossing between, Earth and the otherworld of Eldh. These include multiple villains and world-threatening dangers.
%%* Extremely weird example in ChinaMieville's novel ''Literature/TheCityAndTheCity''. Too good to be spoiled.
* ''Literature/{{Coraline}}'', where the titular heroine must beat the Other Mother [[spoiler: to save her parents and stop Other Mother from kidnapping children]].
* Creator/StephenKing's ''Literature/TheTalisman'' sees Jack flipping between our world and the 'The Territories' in an attempt to save his Mother from dying, this also has the side affect of saving the Queen in The Territories as they share a magical link.
* Most of ''[[YoungWizards So You Want To Be A Wizard]]'' by Creator/DianeDuane is spent in an alternate universe where the [[BigBad Lone Power]] has already put out the sun. At the climax, the protagonists make it back into their own universe, but the Lone Power follows them through the worldgate and they have to stop it...
[[/folder]]

[[folder:Live Action TV]]
* In ''Series/MythQuest'', there is a god named Gorgos who lives to change and destroy mythology. He escapes into an advanced computer system where he has the power to alter the outcome of the myths. Minor changes only seem to cause a ripple effect in global knowledge of the myth, but when he tricked a character into almost causing Ragnarok, a large earthquake was felt in the real world.
* TheFamousJettJackson: Referenced in TheMovie:
-->'''Silverstone''': If Kragg gets this world, it's only a matter of time until he comes for yours.
* The cornerstone of ''{{Fringe}}'' and its mythology is an AlternateUniverse, and the protagonists of the show (from the prime universe) are using MadScience in an attempt to SaveBothWorlds after the first attempt at crossing from one universe to another resulted in a parade of soft spots, cracks in the walls of reality, breakdowns of the laws of physics, [[SwirlyEnergyThingy swirly energy thingies]], [[NegativeSpaceWedgie negative earth wedgies]], [[Film/{{Ghostbusters}} dogs and cats living together]], etc. that threaten to destroy both universes. This is juxtaposed by the characters from the AlternateUniverse, who believe the only way to save their universe is to destroy the prime one first (and they may be right). [[spoiler: Or not, as it is revealed that the two worlds are permanently intertwined; therefore, the only way for any character to save their world is to SaveBothWorlds.]]
[[/folder]]

[[folder:Video Games]]
* ''VideoGame/ArcanaHeart'': An angel with a [[AGodAmI God complex]] is trying to break down the barrier between the real world and the Elemental world. She ''almost'' succeeds.
* ''SonicTheHedgehog'' has this happen twice. Once in ''Sonic Rush'' Blaze is trapped on Sonic's world with the Sol Emeralds. If the Sol Emeralds aren't returned, both worlds will be destroyed. Again in ''Sonic Rush Adventure'', except [[spoiler:Sonic and Tails discover they are trapped in Blaze's world. Eggman and Eggman NEGA team up at the end of the game to steal the Jeweled Scepter, which keeps the two worlds separated.]]
* ''Outcast'': Opening the portal between the two worlds creates a black hole which will swallow up the Earth... unless you enter the alternate universe to figure out how to stop it. It turns out the alternate universe needs to be saved as well.
%%* ''VideoGame/FinalFantasyV'', although it's really more [[spoiler:combine both worlds and ''then'' save them.]]
* ''AnotherCenturysEpisode 3'' features a "save both worlds" plot, as some AppliedPhlebotinum that exists in both worlds creates a dimensional rift, pulling the two Earths together due to gravitational forces. Also connects to ''Eureka 7'' pretty significantly, since it's an IntercontinuityCrossover.
%%* ''Sudeki''. Much like the ''Final Fantasy V'' example, [[spoiler:both worlds get combined and you have to save them.]]
* ''VideoGame/TalesOfSymphonia'' soon becomes this type. [[spoiler: The BigBad's EvilPlan alternates which world is in trouble but]] both ultimately have to be saved for either to have lasting peace.
%%** Also shows up in ''VideoGame/TalesOfEternia'', as an intended result of a YinYangBomb.
%%* This seems the backbone of ''VideoGame/MarvelVsCapcom3'', in which all characters fight in scenerios from both Marvel-Earth and Capcom-Earth.
* ''VideoGame/TheLegendOfZeldaALinkBetweenWorlds'': Link starts out trying to save Hyrule, but soon finds that its counterpart, Lorule, is in even worse shape. [[spoiler:In the end, it looks as though Hyrule will be saved at the expense of Lorule, which would make this a subversion... but Link and Zelda then wish on the Triforce for Lorule's Triforce to be restored, saving Lorule, and making this DoubleSubverted]].
[[/folder]]

[[folder:Web Original]]
* The heroes of ''TheDragonWarsSaga'' must save the magical world they're stuck in to save Earth.
* A key trope in the web fiction serial ''Literature/DimensionHeroes'', in which the Dimensional Guardians must find a way to stop two dimensions from colliding with one another.
[[/folder]]

[[folder:Western Animation]]
* One episode of ''SuperMarioBrosSuperShow'' brings Mario and Luigi back to Brooklyn, but also Bowser and company as well. They have to save Brooklyn and the Mushroom Kingdom from Bowser.
* An episode of the ''[[WesternAnimation/DungeonsAndDragons Dungeons & Dragons]]'' cartoon had the kids finally get back to their own world, but Venger followed.
* In ''WesternAnimation/BarbieAndTheSecretDoor'', the heroines must save the magic of all realms of Zinnia.
[[/folder]]

----