Reality Bleed

A Reality Bleed is where one version of reality is overwritten by another. Unlike when we go Down the Rabbit Hole, the alternate reality comes to us and begins to infringe on the real world.

This is similar to Or Was It a Dream?, but isn't isolated to a specific item or person. Instead, all of reality is up for grabs. If it is caused by a specific individual, they are an extremely powerful Reality Warper. In a time travel story, it would be a symptom of the Delayed Ripple Effect.

This generally begins a little at a time--an anachronistic lamp or the wrong face on a coin--but it gets worse until the process is stopped or it completely supplants the original reality.

This can either be an example of the protagonist going insane, or he could be the only one who realizes that something is very, very wrong. In some examples, everyone is aware of the changes, usually resulting in mass panic.

Due the questionable reality inherent in the presentation of this trope, often the world being changed wasn't real to begin with. Sometimes it's even the real world which infringes on the false reality.

Compare Crashing Dreams, which is when reality infringes on a dream or daydream.

Anime and Manga

 * This happens towards the end of Those Who Hunt Elves.
 * Serial Experiments Lain: What are the boundaries between reality and cyberspace?
 * Paprika
 * Paranoia Agent, made by the same creator as Paprika. ...At least, I think that's what it is.
 * In Noein, this was an effect of Haruka's power.
 * Haruhi Suzumiya has enough of this. The closed space Haruhi creates, as well as an Alternate Universe and the ability to interfaces to warp sections of reality as they see fit (basically making it their own dimension). And then some more examples.

Comic Books

 * In the Crisis on Infinite Earths, this takes place on a universal scale.
 * It's sequel Zero Hour also had this effect.
 * In the fifth-week event The Kingdom, a sequel to Kingdom Come, this happened to Batman in the Planet Krypton restaurant as aspects of the multiverse began to appear inside.
 * In Emperor Joker, after The Joker recreates reality in his own image, tiny reality bleeds from what used to be the real world provide hope for the heroes.
 * In Grant Morrison's Kid Eternity mini-series, this occurs when a folklore researcher witnesses urban legends actually occur in the real world.
 * Morrison loves this trope as seen in his run on Animal Man as well. A second Crisis starts (see above entry), resulting in multiple forgotten "ideas" bleeding into one another.
 * In the X-Men / Fantastic Four crossover "Days of Future Present," this is caused by the Franklin Richards from the Days of Future Past storyline.

Film

 * eXistenZ calls this a "reality bleed-through effect."
 * Cool World. As the film reaches its climax, the toon world begins to infringe more and more on the real world.
 * Pleasantville: After the two protagonists enter the black-and-white world, larger and larger splotches of color become apparent, until the entire world is in color.
 * Overdrawn at the Memory Bank.
 * In this case, it is the main character's own mind that overwrites a fictional reality.
 * This occurs in Franklyn, a 2008 British film. If I remember correctly, it includes one of the rare instances when a reality bleed manages to occur quite quickly.
 * Ingmar Bergman's Hour Of The Wolf. "You see what you want to see."
 * Terry Gilliam's The Fisher King (and many of his films, for that matter) begin to erupt with this trope.
 * Terry Gilliam's The Fisher King (and many of his films, for that matter) begin to erupt with this trope.

Literature

 * Ubik by Philip K. Dick. Glen Runciter's image begins to manifest itself everywhere. And then, although the story is set in 1992, the year 1939 tries to get in on the action.
 * Philip K. Dick loved this trope and also used it in Flow My Tears, The Policeman Said and practically everything else he ever wrote. Heck, his entire Valis worldview was a product of this happening to him in real life.
 * William Gibson's The Gernsback Continuum is about this. The main character is a photographer, and working on documenting 'the future that never was', mostly the future as seen from the 1950s. Then he starts slipping into that reality...
 * Harlan Ellison's Jeffty Is Five is an unusual version of this. Jeffty is a boy who has remained five years old for over twenty years. He can listen to old radio shows on his radio...yet they are new episodes of the shows, episodes that have never existed in the "real world". He can buy comics such as The Shadow and Doc Savage that are, again, all-new although they are no longer being produced, not to mention long discontinued pulp magazines with new stories by Stanley G. Weinbaum, Edgar Rice Burroughs and Robert E. Howard despite the authors being long dead. As reality begins to bleed over into Jeffty's world, it isn't pretty.
 * In the Jorge Luis Borges story, "Tlon Uqbar, Orbis Tertius," an encyclopedia is discovered with a detailed description of the fictional planet of Tlon, which was created over centuries by an Ancient Conspiracy of philosophers, scientists and writers. Everyone is fascinated by the discovery and discusses endlessly all aspects of Tlon. Then gradually objects from Tlon start appearing in the real world... The ending implies that reality will be completely replaced and the Earth will eventually become Tlon.
 * Sort of an odd subversion? Well, something kinda like this was Ray Bradbury's Dark They Were, and Golden-Eyed, where a fledgling colony on Mars starts to gain a peculiarly insightful understanding of the extinct Martians, until.
 * In Terry Pratchett and Neil Gaiman's Good Omens this occurs when a powerful Reality Warper reads too many New Age magazines.
 * In Neal Shusterman's novel The Eyes of Kid Midas, the Amulet of Concentrated Awesome gradually reshapes reality around the protagonist's dreams as he loses control of its power.
 * The protagonists have to stop one of these in Diane Duane's To Visit the Queen.
 * In Terry Pratchett's Mort, the titular character saves the life of a princess who was supposed to die. The princess then becomes the centre of an alternate reality bubble in which she didn't die, but the bubble is shrinking...
 * In the Young Wizards series there's a spell to do this, which is particularly useful for preserving the Masquerade. For instance, say that a bunch of monsters invaded Grand Central Park in New York City. The wizards can cast a spell to find an alternate reality where Central Park is monster-free, copy that version onto their universe, and *BAM*, not only are the monsters gone, there never were any monsters in the first place (except in the Ripple-Effect-Proof Memory of the wizards).
 * Happens in Kim Newman's "The Original Doctor Shade" where an author is hired to revamp an old franchise. However, the original versions of the characters start intruding into the real world and aren't happy with his changes...

Live Action TV

 * A common occurrence in Sapphire and Steel.
 * An odd inversion of this occurs in the Star Trek: The Next Generation episode "Remember Me."
 * A different version comes in "Parallels", but that's because
 * Happens in at least one Twilight Zone episode. In the 1985 series, a man is having trouble learning a new product line, and the words start replacing regular words, a little at a time. Pretty soon no one can understand him, and he can't understand them--even though they're using the same words, they mean totally different things.
 * Occurs the season one finale of Eureka.
 * Doctor Who features several stories where temporal events cause bleedover from other time periods, including "Day of the Daleks", "Invasion of the Dinosaurs" and "The Awakening". Perhaps the ultimate example is "The Wedding of River Song", where all of earth's history starts happening at the same time, and only the Doctor realises anything is wrong.
 * Happens in the season 5 finale of Buffy the Vampire Slayer, when Glory uses Dawn's blood to lower the barriers between worlds and things start bleeding together until the portals can be closed (by Buffy's death)
 * "Nightmares" might also count-a comatose boy's psyche was somehow causing a bleedover and warping of reality and everyone's nightmares.
 * In Fringe, there is an alternate dimension, and the walls are breaking down. Things in one universe begin to affect the other, or are even forced to exist in the same place at the same time, to disastrous effect. The other world has it worse and is becoming nearly unlivable, but "ours" is on the same path, and if unchecked, both worlds will be destroyed.

Tabletop RPG

 * A fast version of this occurred across the entire Earth in West End Games' Torg. Invading "cosms" took over our reality, changing the laws of nature to match their own.
 * Werewolf: The Forsaken has places called verges where the spirit world bleeds into the real world.
 * Mage: The Awakening has Abyssal intruders, some of which overwrite the local laws of reality or the timeline when they visit the Fallen World. One example is The Twisting Maze Zone, which will usually overwrite an apartment building and turn it into a labyrinthine superstructure that extends in all dimensions, including time. Eventually, the building - and everyone who was in it at the time - gets written out of existence because it was never there in the first place.

Video Games

 * The Nanashi no Game series. The haunted video games begin to make themselves more and more apparent in the real world.
 * The Chzo Mythos has this happen in 6 Days a Sacrifice - as each day goes by, the hallway slowly changes to resemble the basement of the DeFoe Manor.
 * The RPG Maker game Visions and Voices is set in a small village that starts out relatively normal. Then mirrors become portals to bizarro versions of the real world, other objects become portals to fantastic dungeons, strange buildings appear, and finally every building in town becomes linked through a bizarre, monster-filled flesh dungeon.
 * This is generally how one finds a deeper layer in the Silent Hill series. The town is relatively normal, if a bit creepy, when suddenly you see a rusty wheelchair.
 * Happens in Fatal Frame 3. The Manor of Sleep and the waking world seem mostly separate at the beginning of the game. As the story progresses, however, things such as the photographs taken in the manor and even the manor's ghosts begin to appear in the waking world.
 * In Guild Wars Nightfall, the world the players inhabit becomes more like the Realm of torment as the game goes on. Completing this process is the goal of the bad guys, while the players are attempting to stop and reverse the process. A couple of zones actually change for particular missions in the story, and later zones in the story have a more "Nightfallen' feel to them as the process occurs.
 * This starts to happen in The Longest Journey, though it's less about one reality overwriting the other, and more about two largely incompatible realities attempting to merge with each other.
 * This is the main problem in Persona 2 (both versions) as the Big Bad starts making every false rumor and conspiracy theory become real just For the Evulz. (The good guys also exploit this by spreading rumors convenient to them.)

Web Original

 * Happens frequently in Homestar Runner. Many things that are considered part of the overall Homestar Runner universe such as Trogdor the Burninator, Sweet Cuppin' Cakes and Limozeen started as Strong Bad's random ruminations. This has been lampshaded at least once.

Western Animation

 * In The Fairly Odd Parents, Timmy becomes obsessed with action movies and wishes for life to become one. No one except him notices the difference.
 * Gargoyles: In "The Mirror", Puck but afterwards they all insist that everything is as it has always been.
 * In one episode of Chaotic, Underworlders appeared in the Real World from the land of Chaotic by means of an inter-dimensional portal, attempting to take it over.
 * In the animated Jumanji, whenever someone cheats, "if you don't come back to the game, the game comes to you".