Saint Seiya. Blatantly obvious in the anime, with the addition of movies and a Filler arc. To the point where greek gods, Norse gods, Buddha, and friggin' Satan fought Seiya and Co.
And the universe was created by Big Bang, so it's possible that Athena reincarnated as a Raptor.
Mazinger Z and Great Mazinger: Dr. Hell joined an archaelogical expedition to the Greek island of Bardos, thinking maybe several ancient legends told that island was defended by an army of mechanical giants were true. Unfortunately to everybody else, he was right. Classical Mythology plays an increasingly important role in each retelling of the series, until the point of Greek gods start showing up and Great MazingerBig Bad is revealed being Hades in Shin Mazinger.
Shaman King also does mention about all prophets/chosen people in different cultures as being Shaman Kings from previous tournaments, although they only imply that with the most known ones, Jesus and Buddha. Some spirits used by shamans seem to be portrayed as Gods, too, like Shamash, and the Sphynx.
Devilman has Akira's friend Ryo tell him that Demons once roamed the Earth before being frozen in the arctic while humans dominated the planet. He also mentions that some demons got free, and could be the true causes of monster myths like Wolfmen, Dracula, and Ogres.
Guyver suggests that the zoanoids changing between human and monster forms is the origin of myths like werewolves and vampires.
A Certain Scientific Railgun has as a running gag the characters mentioning urban legends that all end up being true.
This is brought up in the second season of Spice and Wolf when Holo's past is being discussed.
In YuYu Hakusho, Genkai explains that Botan went to see King Yama. When Kaitou tells her he thought he wasn't real, she says it isn't the time for stupid questions.
Only three legends are ever mentioned in Fullmetal Alchemist, two of which turn out to be true. The Xingese legend of the Western Sage is about Ed and Al's father, while the Amestrian legend of the Eastern Sage is about "Father," the Big Bad of the series. The third myth is presented when Ed compares the circumstances that caused his own amputations to the story of Icarus (of Greek Mythology) flying into the sun and getting burned. Whether the Icarus myth is true in the FMA world is never clarified.
Saiunkoku Monogatari begins with Shuurei telling her students the story of their country's founding, ending it by saying that according to legend, the eight immortal sages who helped the first emperor found Saiunkoku are still alive in secret among the people. This is absolutely true, and Shuurei goes on to become personally (albeit unwittingly) acquainted with several of them.
A little later in the first arc, Shuurei begins to tell Ryuuki the story of the Rose Princess and how she married a mortal man. This story is not only also true, it's the story of her parents' marriage.
High School D×D has alot of mythologies existing in this story, Ars Goetia being the most prominent example. Norse Mythology, Hindu Mythology, Greek Mythology, it's all here though apparently there's also one more mythology that even the other gods of said mythology don't know about. The name of said mythology? There is a breast god in this series.
Lampshaded in issue #4 of the Marvel Universe miniseries Wisdom.
Maureen Raven: Oh, for God's sake, the I Ching is true? Is there anything that isn't true?
This was the original premise of Marvel Comics' Eternals, before they were shoehorned into the mainstream Marvel Universe. The Jack Kirby series had these beings and their enemies the Deviants, mistaken for gods and monsters and inspiring all of humanity's myths, legends and ancient religions. When they got switched to the Fantasy Kitchen Sink of the MU, they were relegated to having merely been mistaken for actually-existing gods.
In the Marvel Universe, ALL pantheons are real. Their leaders have the occasional meeting, for crises such as, say; Skrull invasions?
In fact, the approach taken by Marvel seems to be that EVERYTHING they have ever published- not just the superhero comics, but horror, science fiction, romance, western, humor etc. are ALL TRUE and part of the same setting- details to be worked out on a case by case basis. Yes, even Howard The Duck.
There are exceptions to this policy, but not many. Mostly creator-owned comics like their Epic line of comics are exempt. But even leased properties that they once published but no longer have the rights to- such as Conan the Barbarian, Godzilla or ROM: Spaceknight are still technically part of their universe, even if they can no longer reference them directly! Transformers and G.I. Joe are notable exceptions, they never were part of the Marvel Universe even though it was Marvel that developed them.
In the DC Universe, even if you just look at the Marvel Family, you've got Captain Marvel whose powers come from Solomon and a selection of Greek and Roman figures, as well as his rival, Black Adam who gets HIS powers from the Egyptian pantheon. Both collections of myths spell out "SHAZAM", so they both have the same magic transformation word.
The overarching plot of both Fables and Jack of Fables is, of course, that all fictional characters really exist and are living in New York. Jack of Fables introduces characters that represent literary devices, the most amusing of which is probably the Pathetic Fallacy.
1, Everything you've ever heard about Superman is true. All the different contradictory stories about Batman, they're all true. The "Imaginary Stories" and "Elseworld" comics, they all happened. The Tim Burtonversionof Batman, the Joel Schumacherversionof Batman. The Christopher Nolanversion of Batman, the Adam Westversion of Batman, they all exist and they're all just as real as each-other. Every single alternate version of any character or any story that contradicts anything else in DC Comics, It's ALL true. And here's a list of the different universes each one happened in...
2, also, never mind all that. We're destroying most of the Multiverse and erasing history. You, The Old Superman's busty cousin, your homeworld never existed. You, Batman's Daughter, You never existed and no one knows who you are. You might want to get a new driver's license.
DC is like Marvel in its 'everything we published counts' approach, though with a few more notable exceptions- which of their Vertigo line of comics stories count and which don't isn't terribly clear, for example.
Ganesh: The Earth is so old, and home to so many strange things, that there is hardly an inch of ground that was never home to a shrine, or a god, or a battle, or some magical oddity. Even under the ground, you yourself have said, there are old gods, old prophecies, old lost things. It is not odd that this bound god should be here, in this place. If anything, it is odd that we are not constantly hip-deep in such magical echoes of the past.
Neil Gaiman's The Sandman. Where we learn that not only are all myths true, they themselves take a back seat to an even deeper and all-encompassing group of seven siblings known as The Endless, who embody seven big forces powering all the mythos throughout the entire universe.
To be fair, this is a fairly solid theme in Neil Gaiman's anything.
The Sandman series even basically gives the trope a deliberate nod when one character observes that "A thing need not have happened in order to be true."
I Zombie fits here and may even be heading for Fantasy Kitchen Sink status. It's got the titular zombie, a ghost, a group of vampires, and a were-terrier. And this is all in the first two issues.
The CVO: Covert Vampiric Operations series has this at its core. The titular squad of vampires fights all sorts of supernatural threats. In fact, the only major human member of CVO is their boss Overmars, whose orders the vampires follow without question (most of the time). Overmars's Number Two is an erudite demon named Nikodemus (who looks a little weird, being all red with large horns while wearing a suit). Their scientific expert is a nerdy zombie (who hasn't lost his mind or gained a taste for human flesh). In later issues, they get two more operatives, one of which is a human Genius Bruiser the size of a defensive lineman and a Japanese katana-wielding girl who can turn into a snake-like creature complete with Sssssnake Talk. Their normal enemies include everything from zombies and demons to aliens and Eldritch Abominations. They also have Magitek called Artillica, which appears to be the focus of many issues.
The series lends itself to a number of crossovers. The Infestation arc starts with a new type of zombie with a Hive Mind, capable of infecting any living or mechanical being, which infects one of the CVO vampires and uses her to open portals to four other realities. Conveniently, these realities turn out to be those with which we are familiar: Star Trek, Transformers, Ghostbusters, and G.I. Joe. In each reality, our favorite characters have to fight off zombie infections, which take different forms in each world. So if you've ever asked yourself, What If? Kirk found himself on a planet full of zombies, or what if you had a zombie infection spread to giant robots requiring Optimus Prime to ally with Megatron, then this series is for you.
Following this, there's the Infestation: Outbreak mini-arc, which has aliens allying with demons to escape from the first circle of Hell and invade Earth. The CVO team requires the help of the little grey alien Archibald from the Groom Lake series (apparently, the guy leading the invasion is his drunk uncle Ng, who managed to escape from the facility).
Finally, they find out that the aliens and demons weren't invading. They were trying to escape an invasion of their own realm by the Elder Gods. H. P. Lovecraft is mentioned to have been under control from an Elder God when he wrote his Cthulhu Mythos before a member of a secret society dedicated to keeping the Elder Gods locked away poisoned him. Oh, and this once again causes rips in dimensions, forcing other realities to deal with the Elder Gods as well: G.I. Joe, Transformers, {{Dungeons & Dragons}}, and Teenage Mutant Ninja Turtles.
Fan Fiction
Cosmic Warriors, an AU Sailor Moon retelling, the author starts the story off with the first villain Usagi faces being a reincarnated hero from Irish mythology, Diarmuid Ua Duibhne.
Not to mention (much as some people would like to pretend it didn't happen) stories of extraterrestrial visitation, and theories about Ancient Astronauts.
A variation shows up in Undercover Brother, when Eddie Griffin learns from "The Brotherhood" that all the supposed conspiracy theories about black people are true:
Conspiracy Brother: What do you think? Things don't just happen by accident! Sometimes people — mostly white people — make things happen!
Undercover Brother: So the conspiracies we've believed for all these years are true? The NBA really did institute the three point shot to give white boys a chance?
Conspiracy Brother: Of course!
Undercover Brother: Then the entertainment industry really * is* out to get Spike Lee?
Conspiracy Brother: Come on man! Even Cher's won an Oscar! Cher!
Undercover Brother: Then O.J. really didn't do it?
everyone looks away and mumbles
In Laputa: Castle in the sky, Pazu believes the city of Laputa exists from the start when other say it's just a myth. He's not wrong, otherwise the movie would be a lot less interesting..
The Mummy: "Hamunaptra's a myth." ...No it isn't. And no, the cursed mummy isn't a myth either.
Although the curator who said that knew very well that Hamunaptra wasn't a myth. He was a Medjai who was trying to discourage Evy and Jonathan from looking for Hamunaptra.
Wendy: The stories are true! I swear to you! I swear on everything I adore. And now he's come back to seek his revenge. The fight isn't over for Captain James Hook. He wants you back. He knows that you'll follow Jack and Maggie to the ends of the earth and beyond. And by heaven, you must find a way. Only you can save your children. Somehow, you must go back. You must make yourself remember.
That's far less "all myths are true" as it is "those books that were written are true; I know because I'm the one that experienced it, and told the stories to the writer."
Jerry (reading from a list of questions): "'Is Jesus Christ the son of God?'"
God: "Jesus was my son. Buddha was my son. Mohammed, Moses, you, the man who said there was no room at the inn, was my son."
The TV-Movie series, The Librarian completely runs on this, especially since it's the Librarian's job to find and store all the world's legendary and mystical items in a hidden underground room in the Metropolitan Public Library so that they're be safe and won't be used for evil purposes. The room literally has everything: Pandora's Box, The Goose That Laid the Golden Egg, H.G. Wells' time machine, Excalibur, etc.
Pirates of the Caribbean, which features Aztec and Greek (Calypso) gods, plus Davy Jones, the Fountain of Youth and working voodoo.
Literature
In Erika Griffin's novel, The One Who Waited, Alice ponders this during the course of the story, as she comes to realize that there are such things as Boogeymen and wonders if other monsters might exist as well.
Stephen Marley's Chia Black Dragon trilogy Sorceress, Spirit Mirror, and Mortal Mask, take place in 2nd century China, but there also appear Indian Buddhists, ancient Egyptians (in the back story) and a few Christians. It is suggested that the mythologies and afterlives of all four religions (Chinese, Buddhist, Egyptian and Christian) all exist. In addition to the Stephen Marley's own original myths and creatures, of course
This is the whole point of Neil Gaiman's novel American Gods, in which every god/spirit/devil/etc. that mankind has ever dreamed up are still around, mostly living like normal folks. (For instance, Thoth and Anubis run a funeral parlor.)
In K.A. Applegate's Everworld series, every god from every mythology gets together, and they create a parallel universe where they all rule. Complete with mythical creatures in addition to humans and mundane wildlife. This causes some problems when every god has an extensive cult, and they're all militant. Kill the heretic for worshiping Aphrodite and not Quetzalcoatl! Furthermore, several alien gods from other universes decide to crash the party, including the god-eating god Ka Anor of the Hetwan.
In Rick Riordan's Percy Jackson and the Olympians, the Greek gods are real: features of Greek myths move around depending on where the center of Western civilization is. Olympus is on top of the Empire State Building; the Underworld is in Los Angeles.
On top of that it is also revealed in another of his series the Ancient Egyptian Pantheon exists too.
And the Roman Gods are the Greek Gods' other personality. Is there any god that doesn't exist?
Said series also mentions Moses of the Abrahamic religions.
After finishing with the Roman and Greek gods, he plans on writing a series about the Norse gods.
Robert A. Heinlein's later novels, beginning with the novel The Number Of The Beast (though he used the concept almost 40 years earlier in his short story Elsewhen), deal with the World As Myth, and expand it to the multiverse. In his multiverse, All Stories Are True and Exist, somewhere — and if you've read the stories, it's possible to visit the universe in which the story takes place. He shows this by having his four protagonists visit several universes, albeit unknowing. A side effect of this is that all worlds are part of a story, somewhere... and that anyone who writes a story has become the literal God of the universe the story creates.
In Stranger in a Strange Land, Jubal Harshaw points out one character's objection to a certain religion by logic, leading to the final conclusion that we don't know which god is God, "All names are in the hat."
Harry Potter's world uses this trope, much to Uncle Vernon's dismay.
Children's author Robin Jarvis loves this trope. The ending of the Wyrd Museum series features the deaths of the Nornir by the Spear of Antioch, as well as the ice giants being finally defeated by the Eye of Balor on a spinning weathercock.
True in John Barnes's One for the Morning Glory. It's lampshaded as one of the distinguishing marks of the kingdom, to distinguish it from lands that are merely actual.
The Harold Shea series of short stories features a multiverse much like that of The Number of The Beast.
This was thousands of years ago, remember. Humankind and animalkind were closer then—our years in the Garden together were not so long ago. And our kind, the lycanthropes, were the bridge between the two...It saddens me that the tribes in this country do not tell the old tales to one another. If we gathered to tell stories and drink more, there would not be so much fighting, yes?
In Jasper Fforde's Thursday Next and Nursery Crime series all fictional characters are real(ish) and exist in a parallel universe called the Well of Stories. Fictional characters do have a few traits that differentiate them from "real" people (it's complicated), but in the Bookworld all stories are true.
The entire basis of Robert Anton Wilson's Illuminatus!! Trilogy is that all conspiracy theories are true, especially the ones that contradict each other.
In the universe of Christopher Moore's books the First Nation Trickster God Coyote is the younger brother of the Egyptian deity Anubis, Jesus plays poker with an upstart Cargo Cult deity and there are vampires, djinn and angels, among other things.
The Dresden Files loves this trope. Legendary creatures from the folklore of every part of the world exist, deities from all pantheons are real (though some aren't active anymore), functional magic is an everyday reality, etc.
And despite this, there's still someone around (even people who should know better by now), who get surprised when they find out that something from a fairy tale is real. Like when Harry starts getting stalked by the Billy Goats Gruff.
To be fair, the surprise isn't usually that something is real, but that it's nasty. He wasn't surprised that the Billy Goats Gruff existed so much as he was surprised that they were baddass.
It is heavily implied that these things are not real because they are myths, but myths because they are real - people who had experiences with non-mortals told stories about them that the mortal world consumed. For example, Bram Stoker's Dracula was commissioned by the White Council to educate people about Black Court vampires, who were prevalent at the time (and it worked - Black Court vampires are very rare in the series). Also, Mab has a autographed, personalized original copy of Grimms' Fairy Tales. One reason this might occur in the Dresdenverse is that most Gods Need Prayer Badly.
In his Shadowspawn series, the title beings are the basic for just about every legend of magic or monsters, especialy vampires and werecritters, there is.
In Anthony C. Gilbert's Farther Up and Farther InAll Myths Are True about life after death. Except, apparently, the belief that there isn't any, because the narrator is an atheist but gets sent to Hell, the Christian afterlife being the default for Westerners without other positive beliefs. Escaping from Hell (!) leads to a Crossover Cosmology where he meets Freja, Pan, Monkey and others: the final message (logically, given the opening premise) is that All Gods Are One and we are One with them.
In Douglas Adams' "The Long Dark Tea-Time of the Soul," all the Norse gods and legends are true. Also involves a subversion of Gods Need Prayer Badly, as Thor comments at one point that humanity created the gods, but just because we no longer need them doesn't mean they go away.
I Ching also has a truth, as do other "impossibilities".
In Rainbow Mars by Larry Niven, all of the Martian legends are true, from H. 'G. Wells to Edgar Rice Burroughs.
Robert E. Howard's Conan the Barbarian has a number of gods that would, in Howard's world become the basis of more modern deities. Crom, Lir, Babd, Macha and Nemain are all Celtic, the Hyborian Mitra becomes Mithra, who's also something of a Crystal Dragon Jesus, the Shemite Ishtar becomes the Babylonian Ishtar, the Turanian/Hyrkanian Erlik becomes the Mongolian Erlik and the Stygian Set seems to be the basis for both the Egyptian Set and Apep
The Dalemark Quartet by Diana Wynne Jones features its own in-universe pantheon and myths, all of which are far more real than people believe (and far more factual than recorded history).
The Sookie Stackhouse Mysteries: In addition to vampires, there are Meaneds, shifters, Weres(not just wolves), fairies, demons, witches, goblins, and even vampire Elvis.
To the utter lack of surprise of many, Digital Devil Story, the original source material for the famous Mega Ten video game series, features such specimens as Kerberos, Loki, Izanamiand Set.
In the Tales of the Five Hundred Kingdoms by Mercedes Lackey, all fairy tales, from Russian to Middle Eastern to the Brothers Grimm and anything else, are true. In fact, a magical force known as the Tradition actively works to try and make them come true. Those that are Genre Savvy will use the Tradition to their advantage.
The Bifrost Guardians by Mickey Zucker Reichert is another all myths are true, with the melding of technology to Norse myths to Christianity.
This is the premise of the novel Out of Their Minds by Clifford Simak.
In Prince Caspian from The Chronicles Of Narnia: Caspian was always taught that the "old Narnians" were myths and fairy tales, then he learns that they are in fact real. The appearance of the Pevensies and Aslan also turns out to be this for many old Narnians.
In Orson Scott Card's The Lost Gate the Westillian Families are the basis of all Indo-European pantheons. It is inferred that other cultures deities, including the Abrahamic one have similar origins.
In Djelibeybi, the Fantasy Counterpart Culture of Egypt, all myths are true concerning their gods, which have been evolving and developing for seven thousand years. The priests are said to "never throw away a god in case they turn out to be useful" and to be able to "give headroom to a collection of ideas that would have made a theoretical physicist give in and hand in his badge" (paraphrased).
Also the case with vampires on the Disc — every single vampire myth is true, but they are not all true for any one vampire. Killing them often involves careful questioning about exactly which town the vampire is from, as well as keeping a massive stock of supplies that could potentially be lethal to vampires on hand at all times. As of Witches Abroad, the only sure way of killing them is to set a cat on them — after all, no vampire has ever risen from the cat.
BIONICLE in most cases, the Matoran consider most of the Turaga's stories as mere fairy tales. But most of them wind up becoming painfully true. From giant Manas to the hellish Karzahni.
Vasili Golovachev's novel The Envoy claims that all fairly tales and myths are all true in parallel worlds and the stories are based on the information that is seeping through the walls between them. Any sort of world you can imagine, you can bet it exists somewhere in the Worldfan (yes, even a world that's a giant tree).
In Teresa Frohock's Miserere: An Autumn Tale, any terrestrial religion has rites effective against Hell.
The Secrets Of The Immortal Nicholas Flamel has loads of this, although the characters sometimes inspired more than one myth (and therefore go by multiple names) and sometimes differed from what mundane history and literature said about them. For example, book 4 notes that Aten and Pharaoh Akhenaten were the same being.
A heavy part of the theme of Divine Blood which assumes that evolution resulted in the rising of multiple sentient species all over the world and that humans just happen to be so rampantly successful that everything else has a tendency to mimic them, including species that pre-date humanity by millions of years.
Firebird Lackey: Ilya comes face-to-face with various Russian myths, such as rusalka and bannik and domovoi and sorcerers and spirits. Oh, and there's a dragon, but it's not a real dragon, just a magical construct.
In the 2000s Battlestar Galactica, the humans and Cylon androids both have their own, conflicting, sets of prophecies regarding their mutual future. Series creator Ron Moore has implied in interviews that both visions will prove to be true.
It's possible that the same power was interpreted as a singular god by the Cylons, and multiple deities by the people of the Colonies. In the end, an agent of this higher power reminds another that it doesn't like being called "God", implying that neither perception is entirely true.
As Baltar says in the finale (paraphrased), "Call it God, the gods, a higher power we can't hope to understand, doesn't matter. It exists." In fact, one of the strong threads running through the series is that the Colonials and Cylons have more in common than they'd like to admit, and neither has an exclusive on the truth.
Other examples come along the story of the Cylon D'Anna and her search for hidden truths. First she is given a message from God via a Colonial oracle who also invokes Zeus and Hera. Later the Cylon Hybrid, essentially the Cylon version of an oracle, tells her and Dr. Gaius Baltar to look for the Eye of Jupiter, which is written about in the ancient texts of the Colonials. D'Anna exclaims aloud, "My God. Can there be a connection between their Gods and ours?".
Stargate SG-1 has the Ancient Astronauts version of this, with plenty of snarky comments and Lampshade Hanging to go with in regards to the fact. For example, in one episode, before setting off, the characters all made a vow that dragons weren't real. And yet, by the end of the cliffhanger episode...
Just for list's sake, SG-1 had: Atlantis (Ancients), Arthurian myth (again Ancients), the Greco-Roman mythology (yet more Ancients), the Norse mythology (Asgard), little gray men-style aliens (Asgard again), the fae (Nox), fiery demons and miracle-performing prophets (Ori), and Egyptian and other mythologies with God-Kings (Goa'uld, who also were involved in Greco-Roman mythology). Universe indicated that God, an intelligent creator of the universe, was next on the list. There were a few others, but the alien inspirations behind those myths never showed up again.
The short-lived series Special Unit 2 was about a secret police division that dealt with supernatural creatures, which they call "Links". Lampshaded in the pilot episode, as the head of the division explains all such bugaboos (dwarfs, gargoyles, fairies, goblins, gremlins that hide in the walls) are real "except for vampires—good God! Most ridiculous thing I ever heard!" (a little swipe at Buffy and Angel).
And speaking of Buffy the Vampire Slayer, it specifically mentioned all myths are true in its "Hansel and Gretel" episode. In general though, the series was more a Fantasy Kitchen Sink.
Vampires. Werewolves. Mummies. Demons. (Kitten-eating, poker-playing demons!) Dragons. God(s). Telekinetics. But there's no such thing as leprechauns!
It's even revealed in one episode that there really is a Santa Claus... in the form a demon who comes down chimneys and disembowels children.
In Big Wolf on Campus, everything from Cerberus to Hell to Mummy curses to Medusa to Cyclops to even Santa Claus turns out to be real.
One of the Tales of the Gold Monkey ("Legends Are Forever") had Jack Cutter run into an old flying 'buddy' who had the annoying habit of getting him involved in ill-fated searches for legendary treasure in the constant belief that "All legends are based on fact." He assures Jack that this time he's just on a mercy mission, which has nothing to do with a lost African tribe on an island in the South Pacific...
In any Doctor Who episode, if an alien or a colonist mentions myths of a monster lurking in the ______, the Doctor and his companion(s) will run into it.
Not to mention that the Doctor has met a werewolf, the Loch Ness Monster, sort-of witches, Satan, and just about any other mythical person you can imagine. Oh yes, and he himself is Merlin.
River invokes this at the end of "Flesh and Stone" when she mentions the Pandorica, which the Doctor dismisses as just a story. "Oh Doctor, aren't we all?"
In the episode, "The Pandorica Opens", the Doctor went from "The Pandorica? That's just a legend!" to "So, this is the Pandorica" at unintentionally comical speed.
The rest of the episode at the very least hints that the Pandorica was built by 'The Alliance' based on Amy Pond's memories of her favourite book, Pandora's Box, making this only really APPEAR to be an example of this Trope. In fact, considering the whole point of the scenario 'The Alliance' created, this was probably the intended effect, to try and make the Doctor too interested in what the Pandorica could really be to notice what else is going on around him (And it worked).
Torchwood showed that fairies were real. And alien. When the Doctor on Torchwood's parent show Doctor Who was questioned about "Fairy land" he scoffed. He then went on to say Fairy land looks completely different.
On Supernatural this is occasionally used as a test to see if people are real hunters. It's well known that All Myths Are True, except Bigfoot. And unicorns.
So far, aliens have yet to appear. However, the episode "Clap Your Hands If You Believe" suggests that most (of not all) aliens sightings, abductions, and crop circles turned out to have beenfairies.
Everything in Charmed. Even the stuff that contradicts the other stuff.
HBO's True Blood has its version of this, basically as in All Folklores Are True. Upon hearing that werewolves, in addition to vampires, exist, Jason gets excited and wonders if Bigfoot and Santa Claus are also real.
Dragons too. This, at least, is believable (as much as time-portal anomalies are believable). It's not inconceivable to think of a bunch of Medieval peasants being attacked by a dinosaur and assume it's a dragon.
Warehouse13 assumes everything to be true, and now they have to track down what made it to be true.
This trope has been a staple of the post-Gene-Roddenberry (Read: Rick Berman) Star Trek series. The Bajorans' prophets turn out to be aliens living outside common spacetime and all of their rituals and beliefs generate tangible real-life-experiences. The origins of Chakotay's native american religion are explained and its gods turn out to be aliens. One Voyager episode even hammers the point home that faith and spirituality answer question that reason and science cannot.
The 10th Kingdom implies that all of Grimm's fairy tales and many other myths and legends have their origin in real events from an alternate world that can be reached through a portal in Central Park.
Once Upon a Time, like Grimm presumes that fairy tale characters all actually exist, and where cast into our world by a Dark Curse with no memory of their former lives. The Mad Hatter from Alice in Wonderland has already appeared and in one episode he and Regina visit Wonderland, passing through a chamber with doors presumably leading to different worlds. There are hints that characters from The Wizard of Oz may make appearances as well, not to mention that King Midas already has. Also from Classical mythology are the siren James fights in "What Happened To Frederick" and the two headed snake used to kill King Leonard. Also Sidney was originally a genie.
Captain Hook has now been revealed, along with Lancelot, so all bets are off at this point. It is explained that the stories these characters are based on were inspired by the "real" people living in a different world, and that imagination is a symptom of those worlds touching ours.
Some myths are true in Sanctuary, although usually explained by the presense of Abnormals. Vampires were ancient abnormals who ruled Earth. A group of humans and Abnormals rebelled and fled to Hollow Earth, building a vast underground city of Praxis with highly-advanced technology. The vamps themselves were later wiped out by the rebelling humans. The Hindu goddess Kali is actually an immensely-powerful Abnormal whose physical form is that of a giant spider. There is also a similar powerful Abnormal in the shape of a whale living in the mantle, also capable of causing earthquakes.
In The River all the folklore Lincoln was told as a child turns out to be true.
Star Trek: The Original Series Did this with the episode "Who Mourns for Adonis?" in which the ancient Greek gods turn out to be real and advanced aliens that the Greeks worshiped.
Star Trek: Deep Space Nine features this prominently as it is learned in the first episode that the Bajoran belief in their Prophets is actually well-grounded in reality. The Prophets are aliens that exist out of linear time, which is why their Prophecies almost always come true, because they didn't know it was the future.
The premise of MythQuest is two children searching for their father lost inside a myth world.
Music
All The Myths Are True by Abney Park is basically about this trope.
"I've Been Wrong Before" seems to imply this as well.
Tabletop Games
One White Wolf game, Scion, posits that every single pantheon of Gods actually exists and that the players are all children of those gods. Scion: God hints that it's a case of life imitating art, as the Gods were once pieces of the Titans who shaped themselves according to human myth and were bound to humanity by a force called Fate. All Myths Are True... because the Gods made them be true. Practically every other creature of myth is around as well, either as Titanspawn or a Lesser Divinity, and mythical places are Terra Incognitae. On the other hand, there's no official word on the existence or nonexistence of the monotheistic God. The Titan of Light, Aten, would like people to worship him as such, but...
White Wolf's Worlds of Darkness are a (partial) example of this. There are Vampires, Werewolves, Mages, Ghosts, Frankenstein monsters, Golems, Hell Hounds, Gargoyles, Ghouls, Fairies, Changelings, Spirits, Demons, Geists and many other supernatural creatures that are deliberately left unexplained. In fact, there is a common joke how if you picked 10 people at random, 2 of them would actually be non-human. Of course, this is not actually true, since the number of all these supernatural creatures is extremely low compared to humans, so the Masquerade stands.
In Mage The Ascension, it is strongly suggested that gods are simply mages who have reached immense power, and that these things are either brought into existence by powerful mages or "believed" into existence by the Consensus. The dwindling numbers of various supernaturals is supposedly due to the waning belief (encouraged by the Technocracy).
In Glorantha, principal setting of RuneQuest, all the (non-Earthly) myths about a wide variety of gods and spirits are all literally true. Especially the ones that utterly contradict one another.
In Shadowrun, most myths in the Fifth World (i.e. the perfectly normal nonmagical present (3113 BC to 2011 AD, approximately)) are events that occurred in the Fourth World (the about 5200 years before 3113 BC, the end of which was marked by the sinking of Atlantis). The reemergence of magic and elves/dwarves/orcs/trolls/shapeshifters/dragons/etc in 2011 at the beginning of the Sixth World proved most of the myths true.
Played with, as with nearly every other trope, in Warhammer 40000: there's strong implications that all angelic/demonic/godly/magical sightings throughout history (that weren't outright hoaxes) are basically the work of Chaos and Warp Daemons. Also that the Immortal Emperor was everyone from King Arthur to Jesus... No, not Crystal Dragon Jesus, Christ Jesus. Maybe.
Ars Magica flat out states this trope in the rule book.
Rifts, full stop. Being a Fantasy Kitchen Sink, this trope is a given. Books set in a specific region will always have monsters, characters, demons, gods, etc, based on myths or folk tales from that area.
Video Games
Dominions. The game from this series are basicaly this trope in 4x turn based strategy form, dominions 3, in special.
The grey aliens may or may not be aliens. It's claimed their clones of beings found at Roswell, but since they were cloned, they may as well be shaved apes. In Invisible War, they speak and form their own society, but it's still not quite known if they're actually alien or not.
In pretty much all the Final Fantasy games, if you talk to any random NPC who tells you about some legend, the legend is bound to be true. Magical weapons? Yup. Super-powered monsters? Yup. Maze-like hidden cities? Yup.
Nethack's pantheon is conspicuously patchworked together from a very large number of real-life religions with a couple non-deities and fictional deities thrown in (and then there's the Tourist pantheon...). The gameworld itself is likewise pieced together from both mythical and expressly fictional worlds and entities with a couple original pieces thrown in. On top of that, myth-savvy players are frequently rewarded.
Although the only Nethack deity of any importance is, of course, Eris.
Shin Megami Tensei would be the ultimate game example since you can recruit to your party things like Satan, Lucifer, and any God of any religion you ever heard about, and then some Lovecraftian horrors just for the hell of it.
The Thief games feature vague prophecies which imply that antihero protagonist Garrett is a saviour who will protect the world from several menaces. Though he scoffs at this and finds the prophecies ridiculous, he does end up saving the day as foretold. The trope is especially strong in the third game, in which the main villain is thought by the general public to be just a "bogeyman" and is introduced by quotes from nursery rhymes.
In Kingdom Hearts II, there are Seven Mysteries of Twilight Town, which invariably turn out to be for real when Roxas investigates, and serve as clues to the nature of the world he's been living in. But when Roxas's friend comes along to do the write-up, he assumes it was just a mundane misunderstanding.
Turns out those Seven Mysteries were actually based on Roxas' memory of a mission where he investigated on them alongside Axel. Only till Pence informs them that they are all made up, however. Well, except for the seventh, the only one that differs from the Seven Mysteries of the fake Twilight Town: The one sitting in the tree was actually there, is was a chameleon type heartless.
The Nasuverse. In fact, legendary heroes tend to be even more incredible and terrifying than their legends. Who knew Excalibur could fire giant beams of light?
Actually,they don't.The heroes that are summoned a servants are nerfed in order to allow the servant containers to hold all their awesomeness.
This is really only explored in Fate/stay night, but since they are all part of the Nasuverse, this would apply to all of them. This, of course, can cause contradictions involving the gods in these myths, the myths contradicting each other as well contradicting things that was already established about the Nasuverse in his previous works. However, the myths don't always get it right: As shown in Fate/hollow ataraxia, Angra Manyu is not quite who he was claimed to be.
Turned evil in the form of the Night of Wallachia. Well, not legends, but rumors. Wallachia brings forth any rumor around, good or evil, interpreted in such a way that either direction ends up slaughtering hundreds.
Bungie's Marathon series contains an interesting example. The second game has a single terminal midway through the game that references a S'pht creation myth where the god Yrro (hmmm... sounds like Jjaro) flings a chaotic being into the star that Lh'owon orbits. This terminal is never mentioned by any character for the remainder of the game, even when the Pfhor destroy this star at the finale. This myth then forms the entire plot of the third game, Marathon Infinity. Sure enough, the Yrro/Jjaro stuck a chaotic being in the system's star.
All of the "legendary" Pokémon exist and can generally be found easily if you just look in the right place. The actual details given for them in the Pokedex could be myth as far as the game is concerned, but the various adaptations of the world treat them as true.
The mythological Pokedex entries actually seem to be acknowledged in Platinum, where Cyrus assumes that capturing or defeating Giratina will cause both universes to collapse in on each other, since Giratina and nothing else supports one of them. That gets subverted when the player catchesGiratina...which ends up Saving Both Worlds.
Tomb Raider. So far we've had Atlantis, present-day dinosaurs, giant muscular wingless birds, dragons, aliens, Egyptian gods, harpies, living skeletons, demons, shapeshifters, Arthurian and Norse mythology, undead Thralls, and a hellish Underworld. This is because, at the prime of its time, the series was built on the Rule Of Cool.
Both Persona 2 games. After all, that was a big plot point!
In the Persona series, it can be taken that no myths are true, at least the ones concerning the Personas. The Personas, and the myths associated with them, were all created by the human mind and that is why they and humans are one and the same. At least that is what Igor says.
It directly ties with Jungian Psychology, where myths exist because humanity's collective consciousness thinks so. Humanity acknowledges the symbolism and the archetype of the myth as their attempt to explain how the world was created, making the stories of those gods based on what they believed. In turn, the Personas exist because humanity believes the stories and myths they created, and those gods themselves become real as the Personas or whatever supernatural creatures out there as they are humanity's vision of what they think is the force of nature. Your Mind Makes It Real to its literal sense.
Demon Painter who worked for Igor in the earlier games believes that something supernatural must have existed to inspire the myths in the first place. So he desires to find the true demons.
In Cave Story, you're told that a mimiga that eats a red flower dies right away. It's an urban legend to keep the Mimigas from being tempted into eating them - what happens in reality is much worse.
A set of daily quests in World of Warcraft has you investigate myths about maidens granting powerful swords if done a favor. Naturally, all three of them turn out to be true.
The person who sends you to kill Crawmerax the Invincible says that most people think he is a myth and doesn't really exist. Sure enough, when you get to the designated spot, he shows up. Subverted when the quest-giver is quite surprised that you actually managed to find and kill Crawmerax since he made the whole thing up off the top of his head just to mess with people.
Funny Aversion in Lufia: Curse of Sinistrals remake. At one point you're sent to find the legendary sword, which is told to be forged by the gods and able to cut mountains in half. Just one line after that you're informed that all of that is just legend, and the sword itself is probably not even magical, but that you should get it just to boost the morale of the people. It turns our that the myth wasn't true, but the sword is still good enough to be used by the time you get to it.
The Kings QuestPlayers Guide uses this to explain the Fantasy Kitchen Sink world of the games. Seems that magical creatures, deities without worshippers, magic users, and The Fair Folk withdrew from the universe into a parallel universe in order to survive the onslaught of modernity. The veil between the world is also described as thin enough for things to pass between them on rare occasions.
La-Mulana features dozens of gods and monsters from various mythologies scattered all across the world, Ancient Astronauts, Precursor giants and a special Genius Loci, deliberately mixes myths a lot and generally comes with a very own interpretation of mythology.
In Star Wars: Knights of the Old Republic, you can learn about the creations myths of the Selkath and the Tusken Raiders. It turns out that both are true and are due to the Rakata, the creators of the Star Maps. It's also implied that the Tusken Raiders are the original humans.
The upcoming game The Secret World centers itself around the concept that EVERY real world myth, urban legend, and conspiracy theory is, in fact, true and claims to have entire missions devoted to each of them. This includes, but is not limited to: 11 days are missing, the bees are returning, there's a city on the moon, the earth is hollow, the wagtail has arrived, Stonehenge is a beacon, etc. in addition to the existence of every major mythological creature. In fact, the tagline in one of the trailers is "everything is true."
In Mortal Kombat 9, Nightwolf, one of the few spiritually aware denizens of Earthrealm, identifies Raiden as Haokah, the spirit of thunder and lightning in Lakota mythology. He explicitly calls him such a few times during the course of the story, and Raiden responds to him without hesitation.
What's more, the stories will be told with impeccable detail. A thousand years on, everybody in the world still remembers which particular tooth was knocked out of the mouth of a random peasant by a marauding Bronze Colossus.
In addition, all gods in every religion ever to exist in the world are also real and will ocasionally curse heretics and gift their faithful with different powers (at the moment, just the secrets of life and death). They can even be talked to, but don't actualy answer... Yet.
In the latest update, every person suspected of being a vampire is, in fact, a vampire, and many people will take this as fact. Despite that, the vampires still manage to hunt and kill literally hundreds of people through the ages without ever having their cover blown until the player shows up.
Septerra Core. All Myths Are True... and you can summon them.
Touhou has approached the level of All Myths Are True. In fact, enough belief or disbelief can make something true over the course of time and it will wind up in Gensokyo eventually. There are both noted and suggested subversions and at least a third of the expanded material goes into depth about the differences between some common Japanese myths and "what really happened." One example is Remilia Scarlet: there are so many vampire myths across many cultures, her species of youkai has amassed an incredible number of strengths and bizarre weaknesses and some don't even work as reported.
The King Of Fighters treads a thin line between this and One Myth To Rule Them All, but either way, it's a doozy and a half. Right off of the bat, the Orochi Saga has the eponymous Knight TemplarBig Bad as the human-hating child of Gaia. Yes, the earthly mother goddess of Greek mythology. The backstory of this particular Story Arc is grounded in a retelling of the tale of Orochi and Kushinada-hime where, instead of being felled at the hands of Shinto storm god Susanoo, Orochi is defeated by three clans (and later, their descendants) wielding the Three Sacred Treasures, the Imperial Regalia of Japan that is traced back to Shinto sun goddess (and Susanoo's sister) Amaterasu. The worst part? This isn't even scratching the surface. As KOF continues to integrate aspects of the greater SNK universe, not only are more elements from Japanese and Greek/Roman myth folding into KOF lore, but so is Chinese myth and even Abrahamic tradition. Oh, and don't forget about aliens. They're here too, depending on howyou look at things.
In Bibliography, it's basically explained this way.
Scary Go Round has zombies, vampires, ghosts, sentient gas, sentient space owls, time travel, inter-dimensional travel, witches, wendigos, the devil, devil bears, giant bees, Atlantis...
Used in The Adventures of Dr. McNinja, where if anyone (and that means anyone) mentions anything absurd or unusual sounding, like giant lumberjacks, dinosaur-riding bandito paleontologists, zombie ninjas, or the ghosts of dead NASA astronauts, you can bet it'll not only exist but have a direct impact on the plot of the current arc.
Gunnerkrigg Court seems like a contender for this. It has psychopomps, elves, fairies, ghosts, psychics, fire elementals, valkyries, trickster gods from France and America, among others. It stands to reason that nearly all mythical creatures exist in this universe.
Well... sorta. Coyote is pretty much the Coyote of myth, but Reynardine is more of an allusion than the actual figure of folklore.
Sire: The concept of the comic is that most literary classics are true stories and the ancestors of these characters are being forced to live the morals of their "Sire"s story, succeeding where their originals failed.
Mocked frequently in Slightly Damned. The main character, Rhea Snaketail, was an atheist before dying. Then she went to hell, met a demon and an angel, and discarded her skepticism in a hurry. The comic still pokes fun at everything she thought was a legend being true at routine intervals.
One of the basic sources of all magic, ultra-high tech, and superpowers in the Global Guardians PBEM Universe is human belief. As a result, pretty much every single god or monster any human being had ever dreamed up actually existed, because someone, somewhere believed they existed.
Gargoyles practically named the trope when the Weird Sisters (yes, from Mac Beth) responded to the Archmage's surprise that there was a real King Arthur sleeping under a hill in Avalon by saying, "All things are true". The line has become a favorite answer given by Word Of God to certain kinds of fan questions. In a recent Canon comic book, it was subverted by King Arthur (in reference to Arthurian legends): "All things are true... few things are accurate."
Could rate as an invoked example, as many of the deities and monsters of myths are eventually revealed to be The Fair Folkplaying with this very concept.
Early on in Jackie Chan Adventures, the only thing supernatural was the titular magic talismans and a few Chinese myths, but filler-episodes soon gave way to just about everything you can think of and then some.
Played for laughs in an episode about Stonehenge. Apparently, it has some sort of great magical powers, but nobody really knows what it does. Jackie Chan, upon being told this, sarcastically remarks "Yeah, and some people think it's used to contact aliens." The bad guys figure it must be some kind of weapon, and Jackie Chan goes into action to stop them from activating it. Amazingly, the bad guys actually succeed at pulling off their Evil Plan to activate Stonehenge, revealing to everyone present that Stonehenge does... absolutely nothing. Everyone goes home, and then, in the last scene of the episode, a UFO lands at the now-deserted Stonehenge.
Despite diverse aliens initially being the main shtick, the sci-fi Ben 10 felt the need to make use of this. By season 2, sorcerers, the Krakken, and mall-attacking zombies are all but commonplace. Then they clumsily ret-conned everything away except for the aliens in Ben 10 Alien Force, to the point where everything is alien-based, including super-powered human children.
This trope led to an ontological debate in a three-episode arc of South Park, wherein it is discovered that there's a place known as Imaginationland where everything imagined by people — myths, religions, and deliberate fiction — is in fact real. Turns out, the place is ruled by the "Council of Nine," a body consisting of Aslan, Gandalf, Glinda the Good Witch, Luke Skywalker, Morpheus, Popeye, Wonder Woman, Zeus, and, of course, Jesus.
The last one can be kinda weird considering Jesus is a semi-regular character on South Park, (which has a little of All Myths Are True in its normal world) but then again, his Imaginationland incarnation acts a little differently from the norm and doesn't recognise the boys. See Fridge Brilliance.
In some episodes of Growing Up Creepie, there appear to be paranormal things like haunted bagpipes, living dolls, alien crop circles, etc. Though Creepie soon finds out they're caused by bugs. But by the end of an episode, the paranormal turns out to be Real After All (the bagpipe really IS haunted by the ghost of its original owner, the doll really IS alive and possibly evil, aliens are real, etc.).
In Sponge Bob Square Pants: Nosferatu is real, Neptune is real, the Flying Dutchman is real, and a story that Mr. Krabs makes up on the spot to defraud Spongebob turns out to be true.
The first incarnation of He-Man And The Masters Of The Universe, so very much. Everything that's supposedly just a myth, turns out to be real EVERY. SINGLE. TIME.
Futurama: the in-universe legends of mutants under the city and El Chupinebra turn out to be completely true - as does the more common myth of crocodiles in the sewers.
In Thundercats 2011 The Catfolk-populated magical kingdom of Thundera, stuck in Medieval Stasis, considers technology to be mythical. Stories of "ships that could fly" are fairy tales told to cubs. The populace has become similarly skeptical of the existence of the Book of Omens and Mumm-Ra. In the space of one night, protagonist Lion-O and the Thunderians see their kingdom ruined when old enemies the Lizards invade, bringing with them futuristic technological superweapons, given them by Sorcerous Overlord Mumm-Ra. Lion-O and his Thundercats are then sent on a race to find the very real Book of Omens before Mumm-Ra can get his hands on it.
My Little Pony: Friendship Is Magic has the tale of "The Mare in the Moon." Despite being referred to as an old ponytale, Twilight Sparkle believes the legend and goes to great lengths to prepare for its return. Naturally, it goes on to become the Big Bad of the first two episodes.
Though in a subsequent episode, the scary campfire stories Rainbow Dash tells (apparently using established characters) are only "real" in Scootaloo's nightmares.
Samurai Jack is both this and a Fantasy Kitchen Sink. Jack encounters monsters and magic of all types and all cultures on Earth; Greek, Egyptian, Celtic... You name it. In fact, in the "Birth of Evil" origin story, his sword was created by a joint effort by Odin, Ra, and Rama, three gods from three different mythologies, none of them Japanese.
Real Life
A popular idea from ancient times up through the middle ages was that all the Greek Gods were really prehistoric kings whose followers established cults in their honor. The idea was first officially proposed by Euhemerus.
Many modern scholars actually think this may have been vaguely true to some extent. For evidence they point out that the line between gods and mortals was heavily blurred - there were cults devoted to mortals and there were mortals who later became gods (see Hercules, Asclepius, Psyche, Ganymede, etc).
Related to this was Interpretatio Graeca - the idea that a god from another culture was actually just an aspect of a Greek god. Curiously, this theory may also have some truth to it. It seems that very distantly related societies did have very similar gods. For instance, the Romans had "Jupiter" / "Dispater", and ancient India had "Dyaus Pitar".
The Roman attitude seems to have been "Maybe this new god we've just heard of is real, maybe not, but let's not piss him off just in case."
There's slightly better evidence for certain ranking Nazis (notably Himmler) believing Some Myths Are True.
According to the ideas of Miguel Serrano which combine norse mythology and hinduism, Hitler was the last incarnation of indian god Vishnu, named Kalki, which is said to be destined to incarnate in the world at the end of the kali-yuga, the worse of the 4 yugas which make up the cycle of destruction and recreation of the world, and bring about the saty-yuga, a golden age of peace and spirituality in which all beings are able to ascend to a higher plane of existence. Needless to say, most historians and theologists find his ideas ludicrous at best.
Some fundamentalist Christians believe that every single deity (other than God himself and angels) ever visualized in all of history is actually a demon/fallen angel.
Often including creatures in literally ANY franchise that has a fictional species/magick overtone. Comes complete with the belief that any non-English-word names are actual names of demons/spells, and that roleplaying the series in real life is an actual attempt to summon a real demon, which is that demon's goal.
Believe it or not, the belief that pagan gods are demons was once more or less orthodox in the early Church, which is part of the reason why Christianity came off weird to a lot of Romans at first.
This is also why St. Patrick is Patron Saint of Ireland: He challenged the native priests to what they saw as "magic contests"...but which he, the faithful bishop of the Catholic Church, saw as exorcisms.
The book of Exodus is rooted in this belief as well. The Egyptians were able to replicate three of Moses and Aaron's miracles.
Troy was considered a myth until Heinrich Schliemann found it in the middle-late 19th century.
Speaking of Troy, one of the stories involved a father and his sons being killed by serpents on the beach as divine retribution for opposing the war. While nothing like that may not have ever happened, some have taken speculated that the "serpents" were actually the tentacles of a veryreal creature - one that itself was considered a myth until some remains washed up on a beach.
Most modern Pagans and Heathens believe that each tribe has their own Gods, and that all pagan/heathen paths are simultaneously valid.
This is not just limited to Pagan gods. Mainstream deities are included in this pantheistic belief structure as well. Explanations range from the extreme polytheistic view that all gods exist independently, to the idea that all gods are truly an expression of a single, unfathomable, life force/deity that is given shape to a believer by their own religious needs (meaning, they see "God" how they need to see it, but it's all the same thing).
This is also how religion worked in most of the ancient world; an individual civilization's gods were seen more as guardians of their people than absolute one-true-religion deities. Religious conflict in this era was less, "Your god is false and mine exists" and more, "My god could beat up your god."
The Baha'i faith believes that most of the world's faiths come from God, so most myths are true.
They appear to have found Atlantis (or the city that was the basis for the legend), a city that, as Plato said, was located just beyond the Straits of Gibralter and was organized in concentric circles.
One can pretty much be a Buddhist and anything else including an atheist. The only reason you can't be Buddhist and a Christian/Jew/Muslim is that these religions are exclusionary and won't let you.
Which is actually a misconception, especially when one considers the historical relationship between Buddhism and Hinduism.
And Buddhism and Christianity, and Judeo-Buddhism, etc. Thanks to Syncretism, a great many faiths have roots and branches that intersect. For example, modern researchers will tell you all about the similarities and possible cultural transfer between Buddhism and Christianity, going all the way back to the time of Christ. Of course, Judaism, Christianity, and Islam (among other related faiths) are directly related to one another (with mixed faiths such as Jews for Jesus and Chrislam existing). Then there are esoteric systems such as Sufism that, while based on Islam, have adapted various Near-Eastern and Eastern traditions. This is of course completely ignoring the various denominations and sects that exist within all these religions. People are just so used to looking at things in terms of "Christianity, Islam, Buddhism, Judaism, Hinduism and Shinto" that they forget about all the smaller sects within these groups, and how they are all interrelated in some way to each other (various degrees of separation), while falling under the broad heading of the religions they claim to adhere to.
Subversions and Exceptions
Anime and Manga
The second episode of Baccano gives us the Urban Legend of the Rail Tracer: a monster that slowly snatches up and devours the passengers of the train on which its tale is told on. Then a 3-way war breaks out over train-hijacking rights and...something decides to start picking off instigators and leaving their twisted and mutilated corpses. Turns out that the Rail Tracer is the entirely human and supposedly dead train conductor that first told the story, and doesn't particularly like people messing up his train. Did we mention that he's also a not-entirely-sane assassin that likes a good Roaring Rampage of Revenge?
Fairy Tales
In "Sleeping Beauty", when the prince comes and asks after the castle, he gets a whole slew of false answers; although one old man does know the truth, it's not the popular one.
Everyone answered according as they had heard. Some said that it was a ruinous old castle, haunted by spirits. Others, That all the sorcerers and witches of the country kept there their sabbath or night's meeting. The common opinion was: That an ogre lived there, and that he carried thither all the little children he could catch, that he might eat them up at his leisure, without anybody being able to follow him, as having himself only the power to pass through the wood.
Literature
In the Dune novels, the Bene Gesserit have a whole system of false myths called the Missionaria Protectiva. They purposely spread made-up prophecies that any member of their order can fulfill if needed. Thus, a member stranded on an otherwise hostile world can appear to be The Woman From the Prophecy.
Which ends up biting them in the ass, hard, when Paul Atreides starts fulfilling prophecies left and right and the Bene Gesserit are so used to treating prophecies as fakes and tools that they don't see the messiah in front of their faces until it's too late to do anything about it. Lampshaded by Herbert in one of the Appendixes, an after-action report by the Bene Gesserit that points out all the clues that a lot of people who should have known better ignored. The report concludes that the only explanation is that the Bene Gesserit were themselves in the grip of a higher plan all along: In other words, yep, All Myths Are True and that's what they get for playing with fire.
Nothing's ever simple in Dune, though. That report was commissioned by the Lady Jessica, Paul's mother, who has a vested interest in maintaining the mythos that is part of Paul's power base.
It's also clear that while Paul is a Kwisatch Haderach, he's not the one the Bene Gesserit intended. When discussing the idea, Mohiam only talks about him being able to access male genetic memory. They completely failed to realize the prescience. The only group aware of it before Paul was the Guild and they weren't talking.
In Brandon Sanderson's The Well of Ascension, the Twist Ending is that the prophecies have been deliberately altered by a powerful being in order to manipulate humanity/the heroes into freeing it.
The stories in the Magic: The Gathering anthology The Myths of Magic are false, either because they contradict existing canon or because they contradict each other.
Also from Magic, the name Lord of the Wastes originally referred to a Benalish mythological figure, but was later used as a name for Yawgmoth. However, the description of the Lord of the Wastes didn't match Yawgie at all, other than that they were both evil overlords.
In Philip Pullman's His Dark Materials, many divining methods are actually just "talking to Dust", the sentient matter forming most of the universe. Averted, however, in that most religions may actually be lies created by the Authority to control everything.
Only the authoritarian religions. The others presumably are born from interaction with the Dust, and Angels who are spontaneously formed from it.
The witches worship deities such as Yambe Akka (based on a real world Sami and Finnish goddess, by the way), but there's no evidence for, or against, their actual existence.
Young Wizards plays with this trope, in that many myths were inspired by the non-mythical actions of the godlike Powers That Be. For example, the extremely powerful Winged Defender is the inspiration for (among other things) Thor, Athena, Prometheus and the archangel Michael.
Live-Action TV
Subverted as a Running Gag throughout Buffy the Vampire Slayer and Angel. Despite living in a world where vampires, werewolves, witches, dragons, demons, and zombies are all real and have been encountered by the main cast at one point or another, everyone agrees completely unanimously that leprechauns aren't real.
Fringe started off seeming like a Spiritual Successor to The X-Files, focusing on a unit of the FBI investigating seemingly paranormal phenomena and switching between Monster of the Week episodes and Myth Arc episodes. However, it's gradually revealed that everything paranormal is part of one pattern that began when Walter crossed into an alternate universe to save that universe's version of his son. In other words, what seems paranormal is only psuedoscientific. Also, in one episode, Walter makes it clear that while he believes in many things, he draws the line at ghosts.
The final Quatermass serial has stone circles (which do nothing; the stones only mark the places where people congregated in the past) around the world becoming activated; people congregate there (an activated race memory), expecting to be: contacted by aliens, 'raptured' into heaven, 'go to the planet', etc. Instead, they are 'harvested' by an interstellar energy beam that reduces them to dust, with a tiny fraction lost to the beam. It is further suggested that all religions, and by extension, all of human politics, wars and history, have been the result of this race memory: to congregate and be harvested.
Averted in Babylon 5's episode "A Late Delivery From Avalon"—an arrival on the Babylon 5 station claims to be King Arthur, brought back among humanity after a long hiatus (when he was "taken to Avalon" on a mysterious "ship"). There is actual discussion among the main characters as to whether this could be true, since there was already a known case where the Vorlons did abduct a historical figure and used him to do their bidding in other times ( "Comes the Inquisitor"). But it turns out he was from the present time, suffering trauma-induced delusion from being the officer who fired the first shot that started the Earth-Minbari War years ago.
Tabletop Games
Subverted in White Wolf's Mage: The Awakening, where part of being a mage is sorting through which myths are true and which are not. Note that, in this case, "true" probably means "contains a tiny kernel of actual supernatural, historical or cosmic insight which was either implanted or leaked through into the human consciousness", while "not true" probably means "was deliberately fabricated by other mages in order to mislead those who would seek the truth, was deliberately fabricated by other mages in order manipulate the course of human culture, or was just a myth that people came up with".
The Eberron setting of Dungeons&Dragons has a version of this: in contrast to most settings in which Clerics derive their powers from one of a set of specific gods chosen by the DM and which definitely and demonstrably exist, in Eberron, anything a cleric believes in sufficiently works. Clerics can be devoted to abstract concepts (like "Justice") instead of specific gods, and there's at least one religion in which the followers know their god doesn't exist (yet) because they're in the process of building him.
Arguably, an underlying theme throughout the Elder Scrolls series is that different, contradictory mythologies are all simultaneously true. There were some seven different endings for Daggerfall depending upon the final decision of the player; the succeeding games describe all the possible endings having occurred, despite the contradictions involved.
Played with humorously in Oblivion where Sheogorath asks you (or you ask yourself if you've become Sheogorath) to fulfill a prophecy a small village has about the end of the world that includes attacks by rats and FLAMING DOGS DROPPING FROM THE SKY. The prophecy is used as little more than a prank.
The Game Boy game Final Fantasy Legend II (Sa Ga 2 in Japan) avoids this. One world your characters explore has a myth that turns out to be true and another myth that turns out to be false. Also, there are actually 78 "MAGI", not the 77 that you are told about at the beginning of the game.
Eventually one of the theories turns out to be true: the treasure is an ancient demon. But later it is revealed that the 'real' treasure was a Dried Shroom, the weakest healing item in the game.
Which really isn't very surprising when you consider it was rotting for the past thousand years.
In the same district of Rogueport that Frankly's house is located in, you can find a quirky storyteller who is glad to spin all sorts of old stories. But that tale about the horrible evil monster and the four heroes who fought it before being themselves sealed away couldn't be true, right? Of course it is. The monster is a demon sleeping underneath Rogueport right now and Mario actually encounters each of the heroes in the form of talking cursed treasure chests. They're pretty nice.
In Fire Emblem: Path of Radiance, the heroes learn that a medallion holds a dark god who will bring The End of the World as We Know It if freed, and it can be freed by Magic Music or a huge war. The fact that certain people can become mindless berserkers by wielding the relic reinforces this belief. But in the sequel, Radiant Dawn it turns out to be a lie spread by the Dragon Laguz king in vain hopes that it'll prevent war between everyone in Tellius. In truth, endless war will actually awaken the goddess Ashera, who will see the wars as a sign that those living in Tellius are failures, and must be purged away to allow for a perfect world.
In the Shadow Hearts series all myths are true, though very often in ridiculous, bizarre and over the top ways.
Some of the local legends recounted to the protagonists of Chrono Cross turn out to be... slightly skewed.
Web Comics
Myths and superstitions in Tales of the Questor tend to be problematic after a few too many generations. Some of them end up being accurate, but for each one that actually is, you've got a few dozen that are corrupted from translation issues or pure age, and hundreds that are plain false or started up from illogical premises. It's also a rule for the setting that no one can see the future, so prophecy tends to always be wrong.
Subverted in thisAbe Kroenen comic. Of course, everyone present takes the fact that Atlantis exists in the first place as unsurprising.
Wayward Sons focuses mainly on Greek mythology, but features figures from several other ancient cultures.
This short story from Skin Deep. "How am I supposed to know what is actually fiction around here anymore?"
Web Original
Tasakeru: True in-universe. Each sentient sees their species' version of the God of Time the first time Zero becomes his keshin.
Western Animation
Another "exception to the rule" episode: Ben 10 devoted an episode to the Navajo legend of the Yenaldooshi, as told by one of Max's former teammates. In the end, the Monster of the Week turned out to be a mere alien (though one that would prove to be important later), and all of the folklore was a red herring. Even the parts where Ben was "infected".
In one episode of The Real Ghostbusters, the Ghostbusters must deal with a creature from Irish folklore. According to legend, the creature can only be stopped by a four-leaf clover. All the characters go out searching for one, except Egon, who, playing the role of Agent Scully, insists that the creature can be captured using the same "scientific" methods they always use. In the end, the four-leaf clover fails (it was a fake taken from a parade float), and Egon saves the day by capturing the creature "scientifically", exactly as he said he would.
This troper thinks that the characters should have caught on by now and stopped believing that every single ghost they encounter is real. Not very Genre Savvy of them.
To be fair, only Shaggy and Scooby seem to actually believe in ghosts, which is somewhat forgivable as one is the G-rated version of a stoner and the other is a talking dog.
There are a few times where the monster turns out to be real.
Examples:
Scooby Doo Monsters Unleashed (though this is in a way full of lampshading because the real monsters are made from the costumes of the fakes.)
What's New, Scooby-Doo? includes some rather advanced technology which makes for better disguises and a smart house that causes trouble but just wants attention but also includes a coral monster in one episode. The weird part? It's real. It evolved and was awaken by underwater drilling
In Scooby-Doo on Zombie Island, Fred, in a very Genre Savvy move, says after capturing a zombie that "they should just pull off the mask and get it over with." Cue the Gang looking shocked as Fred pulls the zombie's head off.
Roswell Conspiracies: All mythological creatures are actually aliens who have been on Earth for centuries, or millenia.
Other
BIONICLE has made liberal use of this, though most of the myths have been distorted through the ages, and the rest have other things keeping them from being perfectly straight examples:
In the first few years of the franchise, each time a new threat appeared, the Turaga elders had a legend ready to explain their presence. Eventually, the Toa got rather annoyed with being kept out of the loop until the last minute, finally getting the Turaga to explain just where they got all their information:
The original backstory said that the Great Spirit brought the Matoran out of darkness to the island of Mata Nui. We later find out that it was actually the Turaga who rescued them (as Toa Metru) from their ruined city of Metru Nui, they just credited the Spirit with giving them the strength and abilities to do so. (They also treated Metru Nui's existence as a Greatest Story Never Told to keep the Matoran from remembering and getting homesick.)
One story said that poor workers were sent to the dreaded realm of Karzahni to be punished. In truth, poor workers were sent to Karzahni to be fixed; it's just that Karzahni was a really crappy healer and he never let anyone leave.
One legend that isn't real is that of the monster Irnakk — that is, it wasn't real, until the Piraka entered an area that brought worst fears to life... (Thankfully, Irnakk only existed briefly before vanishing.)
