Mahou No Iroha: Time travel is apparently very possible with the help of magic, and the Magical Girl main character somehow changes some things but not others that leaves readers scratching their head.
Haruhi Suzumiya. The first thing we hear about time travel is that it's like a picture book; it looks continuous, but it's not, and scribbling on one page won't change the ending, so it's impossible to change the future. That gets thrown out the window pretty quick, with time loops up the wazoo. Several space-time locations get multiple time loops overlapping over them at the same time. However, starting in Novel 9, the timeline splits— not diverges, splits— and later fuses back together, and in novel 10 it is revealed that the evil time traveler Fujiwara is from a different future than Mikuru. In his, she's dead—and he wants to fix that, because she's his big sister. Unfortunately, in the timeline she's from (where she survived), her little brother never existed in the first place. So it's possible to change the future, right? Maybe. Because when all this craziness is going on, Kyon brings up the picture book analogy again, and it's confirmed that that is how time travel works (though at the same time it's implied to be an incomplete explanation). The mechanics of time travel in The Verse are pretty much incoherent now.
Tsubasa Reservoir Chronicle: Feather. Reservoir. The fucking up of the entire time-space continuum. Time travel duplicates. Clones? Parents? Putting what is confusing about the time travel involved into words is, in itself, extremely confusing.
When time travel is introduced to Dragon Ball Z it is assumed that Trunks travel backward from his Bad Future and warning the heroes about the Androids means that they will be able to defeat them and change his own timeline. Eventually, he travels back again, and finds that things are not playing out as they did in his own history. This is further complicated by the appearance of Cell, who travelled back from a timeline in which Trunks disabled the Androids before being killed by Cell and having his time capsule stolen. Trunks eventually concludes that nothing that happens in one timeline has any bearing whatsoever on another (meaning that killing the fetal Cell in the "present" won't retroactively destroy the Cell they are fighting, and there is a third Cell waiting for him back in his own timeline, which won't be affected by the Androids being stopped in the "present"). So his solution is simply to deal with the problem in the "present" then return to his future having Took a Level in Badass that allows him to obliterate his Androids and Cell with little effort.
In US Patent #1 by Cheapass Games, each player has invented a time machine and hopes to profit from it, but the only one who will be able to profit is the one who holds a patent. Given that patents can be invalidated by proof of earlier work, the only patent that matters for a time machine is the chronologically first one. So the entire game consists of a race through time to be the first in line on the first day the Patent Office opens.
In Chrononauts, players are competing time travelers from alternate futures sent on missions into the past to recover various historical artifacts. Each player is playing tug-of-war with the timeline so that they can return home, which results in a very fluid history. If enough paradoxes pile up, they can even destroy the universe.
There's a Back to the Future card game based on the film, where again each player is someone from an alternate timeline trying to manipulate the universe into one where they exist. However, one big difference is that after doing so, the time travelers have to stop Emmett Brown from inventing time travel so that nobody else can mess with it and their timeline becomes the only timeline. Paradox much?
In Season 8 of Buffy the Vampire Slayer, Future Dark Willow exploits the time travel confusion for all it's worth to manipulate people to her advantage.
In the 1980s Marvel The Transformers comic, one can alter the past to suit the present. However, there is also the possibility that one travels to a different universe that is simply the same as your own. So thus, any attempt to travel back in time to, say, build a giant cannon to destroy the dark god who created you when he turns his attention to Earth in order to free yourself from his control as Galvatron tried to, can potentially end in failure as it is not your own universe. As it turned out, it WAS Galvatron's own universe.
The DCU has all sorts of fun here, especially when Booster Gold is involved, but it's been proven time and again that trying to Screw Destiny usually ends badly. Aside from that, the Timey-Wimey Ball hurts Booster's head as much as it hurts the audience's.
An issue of Impulse had a mad scientist invent a time machine, and attempt to change the past so that he would rule the world. Impulse and Max Mercury go back in time to stop him, but wind up stuck in the far distant past. Max lectures Bart on the Butterfly of Doom, and how even eating a fish might cause irreparable harm to the future. But then they discover that the mad scientist is now trapped in the past as well. The three of them decide that the best way to get home is to cause as much damage and destruction as possible. Their logic is that if they completely change the past, it will alter the future so much that the scientist will never exist, which means he will never invent his time machine, which means they won't have travelled to the past in the first place, which means they won't actually cause any damage at all and find themselves back home. Confused?
Professor Zoom has (retroactively) had his hands on the Timey-Wimey Ball from day one. In a single issue you see him edit his brother, parents, scholarly rival, and lover out of his own history, apparently to make sure he'll actually become the supervillain he is. It Makes Sense in Context.
Say the word "Kang" to a fan and they'll often shudder. His time-travel schemes are so complex that his future self, Immortus, is another major Avengers enemy, and the two can often be seen fighting each other. To give a sense of scale: most Marvel Handbook profiles are one to three pages long except for major characters like Spider-Man, Iron Man or Wolverine. Kang's gets six pages, and the bottom half of each page is devoted to Kang's timeline, which is chronological in years but requires jumping around from page to page to get Kang's chronological story.
Made even more confusing with the addition of a third iteration of Kang in Young Avengers: Iron Lad who actually kills Kang in an attempt to prevent himself from becoming Kang and ultimately realizes the only way to save the future is to become Kang anyway. If you find yourself confused, know at least that you aren't alone:
Jessica Jones: Is this a time-travel thing? Because I hate time-travel things. Iron Man: If it's Kang, it's a time-travel thing. Jessica: See, this is why I hate Kang...
You can also thank Kang for raising one of the X-Men's greatest foes, Apocalypse.
Limbo in the Marvel Universe (mainly shows up in association with X-Men) is an entire dimension of timey-wimeyness. When the X-Men entered and got separated, both Wolverine and Colossus encountered long-dead versions of each other, and managed to escape just fine in the end. Storm was stopped at one point by her older self, who had remained in Limbo for decades studying magic. And Nightcrawler killed his older self.
Marvel Comics' Adam Warlock, specifically his evil future self The Magus embodies this trope. Adam Warlock met his futureself and immediately The Magus set about trying to ensure Adam would turn into him. This did not work when "Thanos" and the In-Betweener interfered and Adam was given a choice of timelines, wherein he chose the shortest. The Magus appeared again when Adam Warlock attained the Infinity Guantlet and divested himself of his good self (The Goddess) and his evil self (The Magus). The Magus initiated the Infinity War, but was defeated. Later, to seal the Fault in space caused, in part by the Annihilation Wave, The Phalanx Invation, and the War of Kings, Adam Warlock who, as he expanded magical energy slowly started turning into The Magus, used an "unused" timeline to repair the fault. That particular "unused" timeline was the one in which he became The Magus.
Sonic the Hedgehog has an interesting variation at one point. Knuckles, juiced up on Chaos Energy, was given the chance to bring back everyone on the Floating Island through his power. To do so, he keeps bouncing back in time and stopping a certain event. Not only that has bad consequences for him, what he doesn't know is that he keeps futzing up the actual Sonic events, creating timelines such as a pure SatAM world, one based off of the 1995 OVA and a timeline where Robotnik never initiated his coup. At the end, Knuckles decides to stop that and just bring everyone back from the prison the Dark Legion launched them into.
Zipi y Zape: All the story about the time-travel machine built in a barrel revolves around this trope. In the first chapter, the twins use it to transform a wall lizard into its evolutionary ancestor (which turns out to be a crocodile). In all the other chapters, the twins use it themselves; it no longer makes anything appear in the present time, but depending on the chapter, it either just takes them to the past, or somehow transforms them in their ancestor (and, somehow, with all the knowledge and remembrances that those ancestors have). In one chapter, when their mother makes an omelette with an egg found in the past, the twins remark that its strange look is due to the fact that the egg had over two hundred years, even though the time travel should have prevented the egg from aging. Finally, in the last chapter, the twins get trapped in the future when their machine gets broken; strangely, in a rare example of a invertedSan Dimas Time, it's said that house prices were getting higher because of the twins' absence.
In My Immortal, the main character Ebony travels back in time to teach a young Voldemort about love. But when she does, the plot really starts to get strange. A few examples are that characters in the past know what will happen in the present, that items will not work in time-periods where its not invented yet and that people can't die outside their native time-period.
McGonagall: Tell me your conclusions, but please, don't tell me how you figured it out.
This is actually an inversion, or something. The writer doesn't appear to be confused about what kind of time travel is possible; rather, he works very hard to make sure that it follows consistent rules. And the characters know about these rules. But trying to work out the logical implications of these rules results in confused characters and confused readers.
Similarly, Time v3.0, being a Doctor Who fanfic that does its best to encompass all the chaotic mess that was the Time War, uses this trope up, down, and sideways.
Back to the Future has different things happening to the hero as the past is changed. Read the timeline for the trilogy at this page if you have any questions about how it works. There isn't a single concern here that isn't covered there one way or another. To summarize, you can create alternate timelines, and any time it seemsYou Already Changed The Past (like Chuck Berry hearing the song he would later write) it's really just causing the same event in a different way (in the original timeline Chuck Berry did come up with the song entirely by himself).
Bill and Ted's Excellent Adventure establishes that "the clock is always running in San Dimas" — that is, that however long Bill and Ted are in another time, that much time will have passed when they return to their "home time". This is held up for the first film and most of the second... and then utterly discarded for the ending of Bogus Journey, where they zap away for 18 months and return seconds after they left. Of course, the first film kludges it a bit as well — when initially going back to their own time, they actually end up at the same point they left, and have to be told by Rufus that they need to dial 1 digit higher for the next day. Even more odd, Rufus never tells the two of them his name. They hear it from their future selves, who presumably heard it from their future selves who...
The Butterfly Effect has the events of roughly half of Evan's blackouts caused by his older self going back to them, while the other half were normal initially, but could be changed by his older self. One blackout even has examples of both. Also, it is established early on that Evan is the only who has any memory of the old timelines, but at one point another character notices a change in the timeline for no apparent reason.
Déjà Vu starts out well enough, but implies that the detective has already gone back in time and failed. In the original timeline, the love interest dies, and the hero's blood is all over her apartment. So apparently, in the original timeline, he went back and failed. But then in the new timeline, he gets his wounds saving the love interest. He doesn't bleed all over the love interest's place until after he saves her. So how did there end up being blood in the original timeline, but the love interests dies? What's more, the ending finishes without a Stable Time Loop of any kind, so either the changes made will reset or they've created one alternate timeline where everything is hunky dory and one where everyone's dead.
Frequency is one big Timey Wimey Ball. You've got the son talking to the dad on the same ham radio, and even the whole "changes happen in sync with each other" deal. The first time John changes history and saves his father, he suddenly has memories of both timelines, which is promptly dropped for the rest of the film as from then on he only has memories of how things originally happened.
The Lake House was a horrible mixture of Time Travel ideologies. In some ways the timeline is constant — the guy she kissed at the party turns out to be the guy she's communicating with in the past. Yet in other ways the timeline is variable — she tells him how she misses the trees, so he plants one at the place she's going to live at — which she magically doesn't notice having grown until after she sent him that letter. And then there's the grandfather paradox involving the (lack of a) car accident at the end/beginning of the film, causing her to go/not go to the lake house and end up communicating/not communicating with the guy in the first place. And there's also the dog in the past timeline who responded to the name given to it in the future timeline.
The movie Lost in Space contains a plot where the father walks into the future by an energy field just to find his son creating that energy field as a result to build a machine to travel into the past, because the entire family was wiped out as a result of the father disappearing by walking into the future... and the future Smith killing his past self without a second thought or any consequences for himself.
Each Terminator movie uses a different theory of Time Travel, though it's at least consistent within each movie.
Though one persistent law of Time Travel is that things can only Time Travel is they are made of meat (so people, but not the organic fibers of clothing), wrapped in meat (i.e., Cyborg Terminators), can do a reasonably good imitation of meat (i.e., "Liquid Metal" Terminators) or sneak in when nobody's looking (Cromartie's head). Which is to say, the mechanism here appears to be exactly analogous to airport security. The jury still is out on what would happen if you tried to bring a Ham and Fusion Grenade Sandwich with you.
This actually gets answered in the comic book continuity. A group of skinned-up Terminators gets sent back, but bring along an extremely fat human they captured because he's literally a meat bag. Full of guns. Whom the others have to kill to open.
The theory they use is that only living tissue can travel back in time. A deleted scene from the 2nd film indicates that the T1000 traveled back in a sack of living flesh and cut its way free before killing the cop. One inconsistency is a scene originally in the script for the first film indicates that Kyle Reese's partner, who travels back with him, gets fused into a fire escape and is instantly killed. Though as this is removed from the film it doesn't much affect the time portal energy cutting through things in the 2nd film.
In The Film of the BookThe Time Machine (2002), the Time Traveler discovers that he cannot change any part of the past that would interfere with him creating the Time Machine, since it would create a Temporal Paradox. He can interfere with other matters, such as when he goes even further into the future only to see the Morlocks victorious over the Eloi, and afterward returns to the year 802701 to successfully defeat the Morlocks.
James P Hogan had a solution in Thrice Upon a Time. The prospective time traveler induces a grandfather paradox. The universe doesn't abhor it or disallow it or anything, but simply plays out the umpteen zillion iterations of the events in question. A leads to B leads to Not-A leads to Not-B leads to A leads to B... It should go on forever, but on each run-through, quantum randomness causes things to be very, very slightly different (an atom decays or not, a pair of colliding air particle zig instead of zag) totally regardless of anything the time traveler does. Normally they won't make any difference whatsoever, but after a few million or trillion iterations, the randomness happens to align in such a way that it breaks the paradox (i.e., kills his wife in a new way) and lets the timeline continue past it. What we the audience see is merely the "final cut" version of history, the one that didn't get stuck in an endless loop.
Ben 10: Race Against Time includes a bit of this. Eon seeks to use the Hands Of Armageddon to bring his Dying Race to Earth to repopulate, but traveling through time so much has weakened him to the point where he's unable to use the Hands. His plan is to use the Omnitrix to turn Ben into himself (a second Eon), so that he can activate the device and end the reign of humans on Earth. The movie is pretty vague about how it works, but at first glance, it seems as though Eon may actually be Ben, corrupted by himself in his own past. On top of that, when Eon succeeds in implanting himself in the Omnitrix, he declares that "two cannot exist at once", disappearing into a different point in the time stream.
The film version of A Sound of Thunder (if not the book) uses hilariously inconsistent rules of time travel (and those rules don't make much sense before they start breaking them). It's a crucial plot point that the characters keep returning to the exact same point in time, but never run into previous versions of themselves (no explanation for that is given)... until the time they do (no explanation for that either). Plants smash through the walls of a building because the past was changed in such a way as to cause plants to grow larger and more aggressively (no explanation is given as to why someone decided to build the building in the spot where, in the new timeline, a giant tree has been growing for ages — not to mention why the tree that's always been there smashes through the floor while people watch instead of just appearing as it if had always been there). At one point, the characters are unable to travel back to the point in time they want to reach because there's a time disturbance between the present and their destination in the past; the solution? Travel back to an even earlier point and then go forward (if you guessed that no explanation is given as to why the time disturbance is somehow not blocking that too, you've been paying attention). There were explanations - that the changes come in waves, changing things in fits and starts, not all as a whole. As for having to travel further back, that's easy to explain. Think of it as trying to get into a house, but the front door has something pressed against it stopping you from opening it. What do you do? Go in through the back door and then walk through the house to the front door to remove the blockage. Simples!
The film Detention has one of these as a result of several things: a mother and daughter undergoing a "Freaky Friday" Flip that sees the daughter transplanted into her mother's body circa 1992, another kid from the year 1992 undergoing a nineteen-year time warp to the present day (2011), and a nerdy Asian kid in the present day transforming the school's bear mascot into a time machine for a science project. Ultimately, it will result in the destruction of the world... actually, just the destruction of Grizzly Lake High School, because hey, it's not like the main characters know of a world beyond high school.
If you injure the present version of someone, the time-travelling-from-the-future version of the person will immediately show the scars.
The trope is lampshaded on several occasions by the protagonists; criminals who don't really understand how the various time travel paradoxes work, only that trying to sort it out in their heads just gives you a headache.
Subverted in the extended version of the diner scene which is included as a DVD extra: after telling Young!Joe that he's not going to try to explain the effects of changing the past, Old!Joe then proceeds to explain them, using a line of salt — and it actually sorta makes sense.
In Timecop, it's stated that you can't travel to the future because it hasn't happened yet, but later establishes that people had traveled from 2004 to 1994 while 1994 was still the narrative present.
The time travel in About Time appears to have at least two different modes, but the explanation is very scanty. Tim can go back to a previous occasion and change what he did, but then he can choose to either live from that point onwards, or snap forward to where he jumped from and see what the changes have been. The event described in Secret Keeper seems to suggest he can also undo these changes.
Star Trek: Word of God has it that instead of erasing the later series, it just split off a new timeline, so that the later series still happened in the original timeline (dubbed "the Prime" timeline in Fanon) but has not in the new timeline. This gets weird as there are many instances of characters from the Prime timeline traveling back to before the split, which means that if a character from the alternate timeline were to travel back to say, The orbital Atomic Accident, The Bell Riots, or The first Warp Test they would find time travelers from the Prime timeline, which from their point of view doesn't exist. Quite a Mind Screw... or Ass Pull, depending on the variance of your mileage.
Time Chasers, which 99 percent of its viewers know from Mystery Science Theater 3000. It tells - or rather, tries to tell - the story a man who invents a time-traveling airplane who has to repeatedly go back and stop his former boss from stealing and exploiting his invention for his own personal gain.
Star Trek: Generations, contains a nexus which can at once be described as a portal through time and simultaneously interpreted as a veritable heaven which may, in fact, act as merely a database containing the sentient thoughts of all who have encountered it. Kirk's visit to his past doesn't affect the timeline (although one may say this is due to him not actually doing anything to affect it). Picard, on the other hand, experiences an alternate present. While all this could seem viable as time travel, Guinan stops by to mention that Picard can experience the past or the future, the limits of his experiences within the nexus seemingly being restricted to his own imagination. This should leave a very Fridge Logic-taste in anyone's mouth when they realize that Picard and Kirk traveling back to stop Soren may not actually be time-travel but merely a pocket of Picard's own imagination within the nexus. Thus everything that happens past this point in time (i.e. Insurrection and Nemesis) are not actually part of the prime timeline as Picard is actually gone and the Enterprise is destroyed with its crew dead. Note that the new timeline Star Trek could still be viable as there's no mention of Picard or Enterprise D and Generations has no effect on Spock's existence. Basically, if you accept the nexus as a means of time travel then the time line splits. If you argue it as merely Nexus-Picard's mind, then it doesn't.
Heinlein wrote a short story called By His Bootstraps, in which the protagonist exploits a time machine to move himself forward in time. Simple enough. The Mind Screw comes in when he does this by his future self sending back his intermediate self to persuade his past self to enter the machine's portal. When the past self becomes the intermediate self, he attempts to double cross the future self, but that double cross naturally results in him becoming the future self. Follow all that?
For a real, double whammy version of mind screw, read —All You Zombies— which chronicles a young man (later revealed to be post-real-sex change) taken back in time and tricked into impregnating his younger, female self (before s/he underwent said sex change); then he turns out to be the offspring of that union (time-relocated yet again), with the paradoxical result that he is both his own mother and father. As the story unfolds, all the major characters — the young single mother, her seducer, the alcoholic writer, the bartender who recruits him into the time-travel corps, and even the baby — are revealed to be the same person, at different stages of her/his life. How's your mind doing now?
Time Patrol stories are historically well-researched and confusing as hell. Among other things, the future is "uptime" and the past is "downtime," which makes it sound counterintuitively like time is a river that flows uphill. (This is consistent with convention in geology and archeology, where an earlier period is "lower" because its evidence is in deeper strata.)
Ditto in the 1632 series, the Grantville inhabitants from 2000 are "uptimers," the seventeenth century natives are "downtimers."
The same terminology is used in The End of Eternity, where use words like "downwhen", "upwhen", "anywhen" and "everywhen".
Eoin Colfer's Artemis Fowl and the Time Paradoxdoes not actually feature any paradoxes. The prequel on the other hand... Specifically, an island was magically removed from normal time for 10,000 years, but the magic is breaking up and time starts running alternately forward and backward at varying speeds. Holly dies, but Artemis fires a shot backwards in time thus killing the demon who killed her and bringing her back to life. Furthermore, Artemis goes back in time and causes a mosaic of himself to be created hundreds of years in the past, a fact which is only noticed in the present day after he gets back. Artemis questions the first paradox, but eventually gives up trying to figure it out.
In Last Guardian Opal defies Stable Time Loop by having her past self from Time Paradox killed, and manages to survive. What Opal's timeline looks like now is anyone's guess.
The Book of All Hours duology by Hal Duncan doesn't even try to claim to be otherwise. It's such a mishmash of pocket universes, alternate universes, and paradox that causality can't even be seen with a telescope on a good day. Essentially: think of the universe as a huge piece of vellum on which reality has been written. Then crumple it up. Most characters make such a habit of going not just back and forth in time but sideways that one goes back to the day where he, as a child, met his elder self, and that elder self committed suicide... only now, as the elder self, shoots his younger self instead. Nothing happens to the elder.
In Jasper Fforde's Thursday Next novels, not only do the rules of Time Travel make no sense whatsoever, the main character (whose father is a time-traveller) realises this, and often lampshades it. In one book, the rules actually seem to change over the course of a conversation with her dad, but she realizes there's no point in even asking.
In First Among Sequels, there is a subplot revolving around the fact that the time-travellers have mapped almost the entire future and found that Time Travel has not yet been invented. By the end of the book, Thursday and co. have managed to ensure that Time Travel is never invented, and thus, could never have been used earlier in the series. This means that several events from the previous four books including the plays of William Shakespeareand the beginning of all life on earth logically could not have happened. Since many of these events were the results of Stable Time Loops anyway, this is a case of Ascended Time Paradox. Or Mind Screw turned Up to Eleven. Either way, it's probably best just to apply the MST3K Mantra and enjoy the series.
A significant part of the plot of The Woman Who Died a Lot is that the non-existence of time travel in a world where many people know they used to work for the ChronoGuard has actually made the Timey-Wimey Ball worse.
David Gerrold's The Man Who Folded Himself features a time-travel belt, which has the traveller completely paranoid about the possibility of a Temporal Paradox destroying him. It turns out that Temporal Paradoxes are impossible; Time Travel rewrites history except for the guy who travelled through time. Various Mind Screw moments: the protagonist has orgies with himself of different ages, writes himself out of history, has a family with himself as a female, eventually has that written out of history (but his son still exists) and culminates in finally giving himself (as the son, so he's his own father) the time travel device. On the last, the idea of where it came from is explored a couple of times and eventually it's hit upon that it's impossible to know where it came from, the creators must have been written out of history. Oh, and he kills Jesus at an early age. It's okay, he goes back and stops himself after finding out how much it screws with history.
Harry Harrison's The Stainless Steel Rat Saves the World features two overlapping timelines (one of which only has a temporary existence) and a loop. The lead character travels back in time to stop the Special Corps being removed from history, and manages to disrupt the enemy's plan. He then follows them further back in time, landing in an alternate history where Napoleon conquered Britain. He messes up the controls on the enemy time machine, and (after being rescued shortly before the alternate history disappears) follows them forward (but still long before his own time). He finds the villains (after a long time for them — so long they've forgotten everything except that he's the Enemy), but is unable to stop them; they travel back in time, and he's only saved by a time machine — allowing him to return to his own time — which he then sends back with the instructions for what he just did. Finally, he's told not to worry that he didn't stop the villains; they've just travelled to the first place he met them, where they will then travel back and create an alternate history where Napoleon conquered Britain, before...
In A Tale of Time City by Diana Wynne Jones, the titular city exists outside of the flow of history on the rest of the world. From this vantage point, the citizens see that history works like weather patterns — it shifts back and forth with minute details thanks to the butterfly effect and time loops. Basically, a more detailed explanation of the Timey Wimey Ball, where shifts in the time travel theories are explained away as the changing "weather patterns" of time. For instance, on one day in Time City the inhabitants may observe that World War II begins in 1939, but on another day they may notice that it has changed to 1938. Perhaps time in the book is two-dimensional, with Time City time orthogonal to time everywhere else. Except it turns out that the history of Time City can shift back and forth too...
In Thief of Time, it's revealed that, following various alterations to the Disc's temporal dimensions, the "true history" barely exists, and their main job is to prevent the Timey-Wimey Ball from imploding.
In Night Watch, when Vimes travels thirty years into the past to become his own mentor, even the monks aren't sure what's happening.
Lu-Tze: For a perfectly logical chain of reasons, Vimes ended back in time even looking rather like Keel! Eyepatch and scar! Is that Narrative Causality, or Historical Imperative, or Just Plain Weird?
If you try to place the times and events of some books, you will find they take place a couple years before a different book, and at the same time, hundreds of years before the IMMEDIATE SEQUEL of that different book.
Sir Terry himself at one point explained that "There are no inconsistencies in the Discworld books; occasionally, however, there are alternate pasts."
In Johnny and the Bomb, Pratchett explains that most time travellers forget the original timeline when they return to the new one because of the human tendency to accept what's around them as normal; but if you really try (or are reminded of it by some useful clue) you can remember how things used to be.
Animorphs made use of Time Travel occasionally, and each time it apparently worked differently. Different techniques of Time Travel were involved, at least one of which was by use of a thingy created by the closest thing to a God in the series, and another (a Bad Future-esque thing) was just flat-out never explained. The bad future was apparently a dream caused by an advanced being for some reason. Maybe.
Dean Koontz averted some time travel issues in Lightning by virtue of having the Nazis invent time travel, the limitation being that it can only send you forward (and then you snap back to your point of origin when you make the return trip). While this has its own problems, it at least eliminates the ability to murder your mother before she gave birth to you. You cannot change your own past, but you can change the past of anyone born after you so long as the changes you try to make are not contradictory, and you can bring objects back. Played straight in that if a contradiction is demanded, the portal will refuse the forward transfer (this gets the heroine killed in one timeline). "Destiny struggles to reassert the pattern that was meant to be." Sometimes happily, and sometimes not so happily, it succeeds.
The Never Again series starts out simple enough. It seems to follow the many-worlds interpretation of quantum mechanics so that time travelers can do anything they want, but will create a new timeline that never intersects with the old. Then comes the third book, where that is thrown out the window, and the author's attempts to explain what is happening (with a lot of Technobabble about "intersecting universes" and the like) just raises further questions.
The Last Dragon Chronicles: Oh God. There are too many examples to list, though things start getting particularly crazy from Dark Fire onward. Taken to extremes in The Fire Ascending.
Star Trek: The novel Q-Squared introduces several alternate realities, including one based on the Bad Future in Yesterday's Enterprise. However, in this case, when the Ent-D finds the Ent-C, all the crew aboard it are already dead. Afraid of Klingons getting their hands on a Federation warship (even an old one), they scuttle it and move on. Oh, and by the end of the novel, that reality is even worse off, since its Picard and Riker are dead.
World of Warcraft: The novel trilogy War of the Ancients. Despite some dramatic changes (such as saving an entire race that originally went extinct), it's apparently okay to mess with time as long as the end result is roughly the same. Of course, it also helps explaining why said race appears rather plentiful in World of Warcraft after having been said to be extinct in an earlier novel...
In Connie Willis's stories, the time machine sends you not to your target time-and-place but to the nearest point such that your actions will not change history. (This is consistent with James Hogan's theory mentioned above, though the mechanism is not explicitly stated.) In Doomsday Book (which shared the Hugo Award in 1993), a history student aiming for England 1328 lands instead in 1348, where she can't affect history because everyone she meets will shortly be dead of the Plague.
Black Hole High: "Fate": When Vaughn, having traveled back in time to meet his mother, steals her hairclip as a memento, all of history is rewritten so that his parents never meet, his father becomes a familyless loser instead of creating the wormhole, and Professor Z doesn't get a scholarship from his company to go to college. Which is all well and good. What no one attempts to explain is why, in this new history, Josie never attended Blake Holsey High (Though later events suggest that her presence there may have been engineered to keep her close to the wormhole). To complicate matters further, it eventually turns out that both Vaughn's mother and Josie's father are time travelers, so without Pearson's wormhole (the basis for Time Travel), Josie shouldn't exist either.
Charmed has some rather interesting ideas of how time travel works:
In one episode, Chris is taken 20 years into the future as a prisoner by a bunch of evil dudes. Before he leaves, he manages to slip in a comment about the "creaky floorboard". The witches take the hint and brew a potion for him to use as a weapon, which they hide under said floorboard. The camera goes back and forth, showing what is happening in the future (Chris facing the bad guys) and the present (the girls hurrying to finish the potion). It's strongly implied that, had they not gotten the potion ready in time (i.e. before Chris in the future is shown looking under the floorboard), Chris would have found nothing. In actual fact though, the girls could have relaxed and spent hours making the potion, it would still have been there 20 years into the future, provided it was never removed from under the floorboard at a later time. Speaking of which, the writers may just have assumed the potion would be gone after the episode, rather than continually being under that floorboard for the next 20 years.
In another episode, a demon steals little 3-year-old Wyatt's magic powers. Next thing, 20-year-old Wyatt and his brother come time-travelling from the future, saying "We were fighting demons when Wyatt suddenly lost his powers, so we thought we'd come to the point in time where the change occurred and see what happened". This makes no sense in any form of time travel. If 3-year-old Wyatt lost his powers, then 4-year-old and 5-year-old Wyatt wouldn't have had any powers either, all the way up to 20-year-old Wyatt. It would make no sense for him to loose his powers only suddenly at the age of twenty. Not to mention, once they fixed the problem in the present, 20-year-old Wyatt should have never lost his powers in his time at all.
In another, Chris (having time traveled back to the show's present from the future) is corrupted by demonic influence. They make an antidote for it and Piper, who is pregnant with Chris at the time, drinks the potion. Naturally, this cures the adult Chris after she drinks it rather than preventing him from being corrupted in the first place.
Continuum has a literal Timey-Wimey ball, since there are eight pieces that magnetically grab onto each other and when they do so in the presence of sufficient power, it activates and zaps anyone within a certain radius to a new destination time.
Barnabas Collins travels back in time to save Collinwood from the ghost of Quentin. When he returns, Amy and David still remember being tormented by Quentin's ghost, despite the fact that with the change in history, Quentin never died and is still alive.
Despite the times Barnabas is released from his coffin when he travels back to 1897, and then to 1840, he still has a history with the Collins family in the present era.
The fact that Quentin, Tad, and Desmond Collins survived in 1840, thanks to Barnabas and Julia, changing the line of inheritance, does not seem to have any impact on the Collins family in the present day.
The Ghosts Of Motley Hall a series told from the point of view of the ghosts from various eras who haunt a derelict stately home in England discover one Christmas that, for no reason ever explained, the house has slipped through time to the Victorian era. The ghost of Sir George meets and talks to a young boy who is excited about his presents. Sir George realizes the boy is himself, and only then recalls a vague memory of having met an elderly man on Christmas Eve, who he had assumed to be some distant relative whom he never saw again.
The Girl From Tomorrow has a very large one: Tulista travels back through time and retrieves Silverthorn. Taking him out of the timeline should screw with the future, but doesn't, thanks to one very Delayed Ripple Effect. Silverthorn then takes Alana back to 1990, and their presence in the timeline again fails to interfere with the future properly. It's only after Alana takes them both back to the year 3000 that people begin to notice the Delayed Ripple Effect, despite the fact that if anything, it should have interfered with two time periods. They then attempt to resolve this by returning Silverthorn and Jenny to their respective time periods, only to have the capsule somehow U-turn and return to 2500, meaning there are (briefly) duplicates of Alana and Lorien. This is further compounded when Silverthorn builds a Portal to the Past to get some nuclear bombs. This is only resolved when Petey resets the Portal to send Silverthorn and Draco to 70,000,000 BC. Given what Petey says at the end of the series and the events during "Tomorrow's End", it looks like the entire series is actually a Stable Time Loop
Heroes can't decide if they are going for Static Time Travelling or a Dynamic Time Travelling. And that's the least problematic thing.
Strangely, it seems the farther into the future they see, the more pliable time becomes. For example, if Hiro tries to fix something close to the present, for example, saving Charlie's life, or capturing Usutsu, it's impossible. Can't change it no matter how hard they try. However, the apocalyptic future they inevitably go to in every single season so far, they always find a way to avert that. Well, usually, that seems to be changing for season three, and even before that, some things were constant across all the alternate futures. Peter's scar, and Hiro being Bad Ass with a sword.
The Charlie issue was kind of resolved in a "she's already dying" way rather than "time travel won't let me save her" way; this is more or less repeated with his father in the next season (only "it's his time" this time, instead of the already dying thing). As for the random jumps through time... he spends the rest of the season learning to control his ability; it turns out he just needed to get back the self-confidence which he had lost since he realized he couldn't save Charlie. The time jumps are a bit convenient, and that Hiro's explanation makes no sense doesn't help. Not to mention that nothing else they've done with time travel has made any sense. They don't even try to be consistent, it seems. Very comic booky... which is probably the point. Still makes for bad headaches, point or no.
However, The Heroes novel Saving Charlie took the opposite tactic, implying that Time/God wouldn't let Hiro save Charlie because You Can't Fight Fate. Over the course of the story, Hiro lost control of his powers several times in the past while he was trying to romance Charlie and wound up "jumping" to key locations relating to his quest to save Claire Bennet. Eventually, Charlie figures out what is going on, tells Hiro he must face his destiny even if it doesn't involve her and the two lose their virginity together the evening before Charlie goes into work, meets Hiro for the first time and then gets killed by Sylar.
THEN HE SAVED CHARLIE. No, really. Seasons later, Hiro goes back in time, and gets none other than Sylar (the season one Sylar who'd never toyed with the idea of a Heel-Face Turn) to repair Charlie's aneurysm telekinetically and leave her brains on the inside in exchange for non-Time Crash-inducing information about his own future. However, she's kidnapped by the Big Bad of that season, and Hiro doesn't see her again until she's an old woman who's lived a happy life that Hiro wasn't going to undo so he could have her. Still, it was pretty awesome to see Hiro turn "You Can't Fight Fate" into "Up yours, fate!"
According to The Other Wiki, Hiro can change history as long as he doesn't eliminate his own cause for traveling in time. However, while this rule is sometimes played straight (he can't simply teleport Sylar away, as that would prevent him from meeting Charlie in the first place and he couldn't save her) but other times... not so much (his attempts to save the suicidal employee would eliminate his reason for time travel but it never works out that way. Of course, history doesn't actually wind up changing in that case, so it may not be a contradiction after all).
When an Imagin wreaks havoc in the past, it's translated into the present oddly. For example, if you were standing next to a bridge support, and an Imagin went to last year and broke it, you would see it vanish into thin air now (as opposed to, say, remembering that time a year ago when they had to fix the bridge 'cause a monster trashed it). But since it was trashed in the past, it had to have been rebuilt at some point, right? Apparently, when an Imagin breaks something, the fix's Ontological Inertia fails shortly after the time the Imagin went back. Now that's the Timey-Wimey Ball at its wibbly-wobbliest.
When the Imagin is killed, the Timey-Wimey Ball then uses the original memories of people in the future to repair the damage to the past. However, anything or anyone who is not remembered is not restored. So now no-one remembers the bridge getting repaired because as far as the great unwashed masses know, it was never broken in the first place.
In the crossover movie OOO, Den-O, All Riders: Let's Go Kamen Riders, an elaborate Temporal Paradox was revealed when we learned Naoki is Mitsuru's father. They didn't even try to explain it. This is a paradox because Naoki was stranded in the past after time had already been changed. The version of 1973 that led to the 2010 we know did not have Naoki in it. Therefore, Mitsurushould not exist in the 2010 we know.
The original Kamen Rider has two friends of Goro's by the names of... Naoki and Mitsuru. We meet them in the latter third of the series. Whether Let's Go Kamen Riders is trying to say that they are the same ones and we didn't know they were time travellers is hard to tell, but if that's what it means, it's certainly interesting. However, this adds another level to the timey-wimey: a 1973 with Let's Go Kamen Riders having happened led to the Kamen Rider universe proceeding in the manner we saw in the older shows, even though the whole movie is that the Den-Liner gang's trip leads to a Bad Future which got a happy ending in the present, but can't ever be erased.
The Stargate SG-1 episode "1969" dealt with a Stable Time Loop. Following that, however, all the Stargate series have just treated time travel as only affecting things after the initial entry point. Time is changed in both "2010" and "Moebius" without creating a stable loop. Same with "Unending". The DVD movie Continuum is a bit more complex, since it added a new element to the mix, but ultimately results in the same thing.
Stargate Atlantis had two episodes in the vein of "2010" and "Moebius", following pretty much the exact same conventions in both.
Stargate Universe also sticks to the formula, first with the episode "Time". A Kino is found, which has a recording of horrible death. This recording shows a way to avert it, but they fail to do so and send a second Kino back. That one, along with the first, does the job. Then comes "Twin Destinies". In this one, a wormhole connected to Earth from inside a star somehow catapults the entire ship back in time. Telford (In the time shifted ship) goes through the gate and makes it back to Earth, while the rest of the crew (except Rush) go through when the gate is unstable and get transported to a local stargate hundreds of years in the past while leaving behind Rush, who stays on the ship. The current timeline crew stripped the time-displaced copy for parts, while the extra Rush and the original Telford on Destiny died. Meanwhile the version of the crew sent into the past establishes the civilization of Novus, leading to the present day crew eventually meeting their own decendents in the following two parter.
The series has the relation between Benjamin Sisko and The Prophets. While it appears to be a Stable Time Loop, there just enough wrong with it that it fits here. In the first episode, Sisko meets The Prophets, who live outside of time, and have great difficulty even conceiving of a 'linear' existence. They and Sisko have a nice chat, and Sisko tells them that the Bajorans revere them as gods, it seems that The Prophets weren't really aware of this. It gets tricky from here... As the Prophets seem to 'get' their position, they then (not that the flow of time should mean anything here...) start doing all the things that they are revered as gods for. Okay, one loop, fairly simple Ontological Paradox. Later on, viewers find out that Sisko was born from a relationship his father had with a woman possessed by a Prophet with the explicit purpose of conceiving Sisko. So, Sisko visiting the Prophets made it possible for him to be born in the first place, so that he could visit the Prophets and tell them that they were gods. Keep in mind that if Sisko didn't tell them they were gods, they wouldn't need Sisko, they would have just kept on being non-linear, not to mention the enormous effect the resulting lack of religion would have on Bajor. Now what really twists the boat is that The Prophets are supposed to exist outside time, yet they clearly change after Sisko's first meeting. So they possess both timelessness (from being able to interact with anytime freely) and their own timeline (Which is clearly affected by Siskos visit) These paradoxes and timey-wimey balls are not really explored in the series (though more 'common' forms of time travel are) and the series can be enjoyed without worrying about the timeline of timeless entities. Still, there's rather a lack of coherency.
The whole thing gets kind of lampshaded, when two versions of O'Brien try to figure out the paradoxes and give it up, simultaneously saying, "I hate temporal mechanics!" The episode in question, "Visionary", is quite Timey Wimey in itself, as O'Brien keeps jumping five hours into the future and back, with varying changes once the station reaches that point he jumped to. He even avoids death twice, first by avoiding a booby-trapped surveillance device that killed his future self, then by having Dr. Bashir perform a specific scan on him after finding out the results of his own autopsy. In the final jump, though, Past!O'Brien ends up dying from radiation poisoning, sending Future!O'Brien back 3 1/2 hours to stop the Romulan attack on the station. The resulting O'Brien has issues with his place in the universe for a while afterward.
Star Trek: Deep Space Nine's Sisko and his companions are visited by the Department of Temporal Investigations in Trials and Tribble-ations. The agents mention that they have an extensive file on captain James T. Kirk. They also hate Predestination Paradoxes and jokes.
Star Trek: Enterprise: The whole Xindi arc is a big Timey-Wimey Ball. So the Sphere Builders tell the Xindi to go nuke Earth, because they know (through their semi-time-travel) that in the 26th century, Earth will come kick their ass. So the Xindi go do a preliminary Earth nuking, which causes the Humans to come over and kick their ass, now. The Sphere Builders misled the Xindi into believing that humanity will destroy the new Xindi homeworld, because the Sphere Builders knew that, in the 26th Century, the Federation (which by then will include the Xindi) will decisively defeat the Sphere Builders at Procyon V.
In the 29th century, The Federation has become a sort of Time Police, making sure no one messes with history. The fact that the previous (chronologically) series have never had a problem with timecops showing up is not addressed. They were even admonished that they ought to have been held to account before. Not to mention, if they did, the audience would never know about it...note Mind you, if 29th century The Federation were to start messing with events that happened in their past, that would itself create a time paradox, and thus their own rules prohibit them from policing any temporal incursions that occurred prior to their becoming the Time Police.
The episode contained the morally questionable practice of arresting and trying a man for a crime he had yet to commit. The rather profound implications of this are casually Handwaved with an assurance that he'll be combined with his future selves somehow before the trial, never mind that said future selves are already part of a Temporal Paradox since it would presumably be impossible for him to carry out the crime once he'd been arrested for it. This might not be so troubling if it weren't clear that his future selves were suffering from some kind of severe psychological breakdown, the present self would not decide to commit the crime for many years and thus could not be said to have intent, and being removed from command at this early point would have prevented said psychological breakdown from occurring in the first place. Given equal apparent opportunity to prevent someone from becoming a criminal before it was too late, or punishing him for merely being capable, under the right circumstances, of going through with it, which would you choose? Apparently The Federation, at least according to Voyager's writers, prefers the latter. And the guy's future self was only mentally unstable because said Time Police had already "somehow combined" him with yet another version from an alternate timeline, who had been stranded for decades as a homeless guy on 20th century Earth. One would think they'd get the hint that "combining" people from different timelines is a bad idea...
Star Trek: Voyager also had one of the most illogical time travel plots. They're passing a planet and detect a massive explosion. They investigate the planet and find no life. Janeway and Paris are transported back to before the explosion. It turns out that Voyager's attempts to reclaim them caused the explosion. Janeway stops their next attempt by firing her phaser into the time-portal technobabble thingy, which pushes the Reset Button and they pass the planet without incident. The entire episode ignores that they never intended to go to the planet in the first place, so the whole thing never should have gotten started, since there never would have been an explosion to cause them to investigate.
A quote from Jonathan Frakes re: Yesterday's Enterprise: "To this day I do not understand Yesterday's Enterprise. I do not know what the fuck happened in that episode. I'm still trying to understand it ... but I liked the look." This would become pretty darn Hilarious in Hindsight, given his Trek cinematic directorial debut featured both time travel and a revamped color scheme for the Enterprise.
This one isn't all that hard as far as paradoxes go. During the Battle of Narendra III, the Enterprise-C made a Heroic Sacrifice against the Romulans attacking the Klingon outpost. This selfless act by a Federation ship on behalf of the Klingon Empire eventually led to a peace treaty between the Klingons and the Federation. However, during the battle, a massive explosion caused a Negative Space Wedgie to form, sending the Enterprise-C to the present. But without the Enterprise-C's presence at the battle, the peace treaty would have never formed, either because their sacrifice made the necessary improvements or their disappearance convinced the Klingons that the Federation were Dirty Cowards and things got worse. So once the Enterprise-C arrives in the present, the present almost immediately becomes a Bad Future where the Federation and Klingon Empire have been at war for decades. As a Klingon, Worf would be fighting against the Federation. Tasha Yar is presumably alive because the Enterprise-D never went to the planet she died on, because it is a warship not an exploration ship. The Enterprise-D helps repair the -C enough to send it back through so it can be destroyed as it should have. But Tasha Yar, who in the Bad Future survived when she died in the "normal" timeline, volunteers to go back with the -C after being told by Guinan that she would not live when things go back to normal. So the Enterprise-C goes back to the Battle of Narendra III and is destroyed, but the results of the battle are changed just enough that captives are taken by the Romulans, including Tasha. So all in all, a bit more difficult to follow, but not all that hard to understand.
While each Terminator movie managed to be internally consistent, The Sarah Connor Chronicles combined the continuities of the first two movies and then added some of its own time travel plotlines. Predictably, it's getting a little weird.
The episode "Complications" is particularly troublesome. It introduces a new stable time loop and strongly implies that Derek and Jesse don't come from the same version of the future.
Later in the series, there's so much timeline alteration going on the human time travelers start using the ever-shifting date of Judgment Day to determine which timeline they came from.
There's also the terminator that was sent to the wrong year and ended up having to build a building. Things get complicated when you try and work out how such an early intrusion into the timestream plays out with all the time-travel shenanigans already going on. Being a new model terminator at the earliest point in time raises many questions. Did that one with new orders cause the current events? Would it still arrive in the past if that chain of events were excised?
When a Mad Scientist/Children's TV host proposes that everyone's lives are strings and if you could tie the ends together you should be able to travel along that string, Sam agrees that he is basically right, but that it is important that you ball up that string first so that all the days of your life touch. Which makes sense.
As revealed in the finale, all time travel is monitored by God to create the best possible timeline and presumably keeps Leapers and good people from being erased by paradox and such.
Timeslip, a 1970s British series, presented a form of time travel where the past, not "really" being able to "happen again" is "fixed" — by which they mean that you can interact with the people there, but not alter events, and can be hurt, but not "seriously". In the first serial, a time traveler is shot dead, and collapses, unconscious, leaving blood, but no wound. She wakes up, but still feels the pain of having been shot. You get the first minute of a muddled explanation about it being a sort of shared hallucination before it's dismissed as too complicated to explain.
7Days. It is a rather harsh ground here, since the time machine is alien technology that was badly fixed by humans and due to possibly some screw up (or just plot convenience) it has all kinds of weird side effects. Anyway, when it works like it is supposed to do, it sends you back seven days and your old self and the time machine vanish, either erasing the "bad" timeline or creating an alternate. It is consistent in that. People notice the machine and him vanishing, the episodes are just mostly centered on Parker and until he makes his call they don't know what happened.
There was an episode where an accident during time travel splits Parker into a good and an evil version. The good version is killed, so the evil version is sent back in time again, creating another good version.
It's difficult to count the number of times the machine has not worked right. For just a few examples: it brought a person back from the dead (nearly unraveling all of reality), put Parker into the body of Pope John Paul II, created a Mirror Universe (almost literally, since all writing is in mirrored English), etc. It's a wonder the aliens don't show up to tell the humans to stop messing around with technology they don't understand before they destroy the universe. Then again, they probably don't know and have never bothered to look for their missing prison transport (or that other ship that crashed in Siberia).
Just about any time travel episode, but most especially the Season 6 cliffhanger in which the Dwarfers' scary future selves blow up Starbug, apparently killing everyone on board. Season 7 opens with Lister explaining direct to camera that, because they'd been killed, their future selves never existed to come back, therefore they hadn't been killed, and this is also why Starbug is suddenly bigger. The intelligent video camera suffers a nervousexplosive breakdown trying to understand this.
And later in that same episode, The Boys From the Dwarf violate the same laws that allowed them to survive after they take John F. Kennedy back in time to assassinate his past self!
In "Future Echoes", Rimmer tries to explain Timey Wimey to Lister:
Smallville had a situation in the episode "Homecoming" that was similar to the Doctor Who "Time Crash" short mentioned above; Clark, briefly stuck seven years or so into the future courtesy of Brainiac 5, slips into the Daily Planet's elevator, where his older self is waiting for him. Older Clark orders younger Clark to go to the Planet building's roof to prevent Lois' helicopter from crashing while he(the older Clark) prevents a nuclear reactor from melting down as Superman. When younger Clark asks his older self how he knew to wait for him, older Clark simply answers, "Time travel. Work it through." He knew because he had lived the same situation seven years ago.
Supernatural: "In The Beginning," established that while time travelers can make small changes, they will ultimately lead to the same result because destiny cannot be changed. This is ultimately proven true when Dean's attempt to protect his family from the Yellow-Eyed Demon ends up causing his mother to make the deal with him that eventually kills her. "My Heart Will Go On" blatantly contradicts this by having an angel go back in time and stop the Titanic from ever sinking, preventing anyone on board from dying and leading to hundreds of their descendents who originally never existed appearing in the present. However, the angel who un-sinks the Titanic also states that ever since the Apocalypse was averted, the old rules no longer apply (presumably because the Celestial Bureaucracy is in disarray and can't afford to be watching over every minute detail in order to ensure that it all leads up to its supposed "destiny" anymore.) "Frontierland" circles back to no major changes, but it's a little unclear whether Sam and Dean's actions are a Stable Time Loop or You Already Changed The Past.
This is a fundamental quality of Warp travel in Warhammer 40,000, given that the flow of time relative to realspace changes randomly during transit. Navigation for The Imperium of Mankind requires the use of psychic Navigators to essentially feel their way to their destination, avoiding the worst of the warp storms and riding favourable currents to reach their destination. However, given the abovementioned mutability of time along the way, when you arrive is anyone's guess. The crew could be in transit for weeks or months at a time to arrive at their destination at the same time as when they left, centuries late, or even before they set out, if you even get there at all. A graphical history for a given ship would more closely resemble a circuit diagram than a timeline if plotted out.
Deconstructed in Bastion. The narrator gets several serious cases of deja vu retelling the story of The Kid to his audience, and one of the game's endings directly lead into the beginning of New Game+.
Completely averted in the upcoming indie RTS Achron. The time travel is completely consistent, despite the game handing the players tools to: change the rate time flows around them, give orders to units in the past, send units into the past using time travel, and create time paradoxes... in competitive multiplayer. Bonus points for the system still managing to be fairly easy to learn.
While Chrono Trigger was generally consistent about how its time travel worked, there were a few odd instances.
Somehow Marle paradoxed herself out of existence, despite time travelers not being directly affected by any other changes they'd made during the game. For instance, you can save Lucca's mom, but Lucca still remembers when she was crippled instead of having all her memories changed. Or when the future Robo came from was erased from existence without affecting him.
The Timey-Wimey Ball also applies to game mechanics: One can open a chest in the future, return to the past and open the chest again to get two items from the same chest.
This also means that it is possible to beat the optional dungeon at the end of the game 3 times. However, if you start by beating the earliest version of it the newer versions will also be empty.
According to the staff members, they never quite got a consistent set of rules down for time travel until they had already written themselves into a corner, so they just went with what they had.
Chrono Cross tries to patch things up by using parallel realities as the ultimate outcome of fiddling about with temporal mechanics, and then showing the physical effect of a catastrophic temporal paradox via the Time Crash (wherein a time experiment pulled a city borne from the "good" future into the "bad" future, thereby destroying it, after which it froze and was pulled back to the game's present when the laboratory conducting the experiment, and its opposite number from another alternate reality, were ripped from their native timelines.)
Legacy of Kain. Time-travel, paradoxes, Decoy Getaways, and so much more! It would take an entire page on its own to list everything... but you can always see for yourself at the other wiki.
Then there's the Song Of Storms. Link learns to play it on his ocarina from the Windmill Guy, who's ticked because "some Ocarina kid" came 7 years ago and played it, messing up the windmill. Guessed who the Ocarina kid is? And how he learned the song? That's right, from Windmill Guy, 7 years in the future. Of course, by itself a mere ontological paradox isn't enough to claim this trope - it is after all a very common hazard of Stable Time Loops - but when you combine it with the timeline split...
This is repeated in The Legend of Zelda: Oracles of Ages, during a Chain of Deals no less. The one link involves getting an antique vase from one Goron in the present, who claims it's a cherished family heirloom passed down through generations. Your next link is to give it to his ancestor 400 years in the past, who promises to cherish it and pass it on to his children. ...Just let that one go.
The Legend of Zelda: Majora's Mask is even worse about this. Link is stuck in a "Groundhog Day" Loop that lasts for three days. Whenever the loop starts over, his actions in the previous loop are erased. There are no time travel duplicates, which erases the possibility of another Link running around doing things you've previously done. Instead, they simply don't occur unless you go and do them again. Despite this, once you defeat the final boss, all the cycles you've completed are somehow merged together without explanation and everyone is saved, rather than just the people you helped in the final cycle. Even if you speedrun this doesn't make any sense since the game cannot be fully completed in a single cycle (one sidequest in particular has to be done at least twice in two different cycles with slight variations for 100% Completion). This was probably just done so that the game could have a happy ending, but it seems to break the game's own rules about how Time Travel works. Maybe the Goddess of Time did it.
In four games, the precise nature of time has never remained constant. Ocarina of Time contains at least two very different mechanics, which theorists often find irreconcilable (and downright strange). Ages mechanics only begin to make sense when one sacrifices logic to storyline completely, and Majora's Mask'' Goddess of Time takes the whole thing to hell by drawing questions of omnipotence into the debate.
—The Internet, Trying to solve the mess that is the Zelda Timeline.
The Legend of Zelda: Skyward Sword continues the tradition with Timeshift Stones. When hit, they revert the area around them to several hundred years in the past. Oddly, however, any change you make in the present near one of these stones will still be there in the past. And then, near the end of the game, Link uses the Triforce to kill Bigger Bad Demise in the present. However, Ghirahim kidnaps Zelda and uses her to free Demise several centuries in the past. Link follows him back and seals the past Demise within the Master Sword, which he leaves in the past Sealed Temple. None of this is shown to have had any effect on the timeline when Link, Groose and Zelda return to the present in the ending. The funny thing is this could have worked as a Stable Time Loop had they trapped Demise in the Sealed Temple again instead of in the Master Sword.
Even weirder is that the first time you visit the Sealed Temple, you can see the crystal Zelda eventually seals herself inside which is created later in the game, but in the past. The Master Sword, however, doesn't appear until the end of the game, even though that also happens in the past. Also, near the end of the game you gain the ability to travel between the past and present at will. You can do this without consequence, even though Demise has been freed in the past and would presumably have wrecked havoc on Hyrule and Skyloft without Link to stop him. He does say he would give Link time to prepare before their final battle, but you'd think after several hundred years he'd have gotten tired of waiting.
MapleStory actually uses this term during the Silent Crusade (considering it's unclear how time travel works in-universe or whether it can actually cause changes, makes it fit):
"I found some other timey-wimey dimensional place! It was neat! Oh, also the Goddess of Time was there!"
The Prince of Persia Sands trilogy is one massive example of timey-wimey craziness.
At the end of The Sands of Time, the Prince entirely reverses the events that just took place, making it so the events of the first game don't happen. This creates a paradox.
In Warrior Within the Prince is being chased by the Dahaka, a timeline guardian who is trying to ensure that the timeline proceeds as it was meant to. The Prince inadvertently creates a Stable Time Loop when he kills Kaileena and creates the Sands of Time, the very thing that he was traveling back in time to prevent. Then, he discovers a way to co-exist with himself in the same timeline, which he uses until his normal self in the past timeline is killed, allowing him to remove the Mask of the Wraith.
At the end of the second game, he has killed the Dahaka and successfully prevented the Sands of Time from ever being created, causing another disruption of the true timeline.
In The Two Thrones, the Prince discovers that his paradoxical actions in Sands of Time mean that the Vizier was never killed and war has been unleashed on his homeland. The Vizier captures and kills Kaileena, once again unleashing the Sands of Time and effectively repeating the events of the first game in a different setting. The Prince eventually kills the Vizier seals away the Sands again and seems to have learned from a all his futile time-travel, as he leaves the end of the game be with no further meddling.
Episode 204 of Sam & Max, "Chariot of the Dogs", focuses on Time Travel. This is Sam and Max; any time travel plot WILL bring in to play every time travel concept as fast as it can for the parody.
Several stable time loops are created, including one that is required for getting Sam and Max to the time machine in the first place and another that comes into play in episode 205. However, as if completely ignoring the idea of stable time loops, much of the puzzle solving revolves around completely altering the time stream just so that you can fix a problem created by Max's personality the moment you start time travelling.
One section even has Sam and Max accidentally letting themselves from the first season take their time machine, effectively rewriting everything the player had done in the past year, AFTER a needed macguffin to advance the plot was taken out of the time stream.
Day Of The Tentacle, is extremely wibbly-wobbly timey-wimey. The game runs on San Dimas Time to allow the characters to flush small, inanimate objects to each other through time via their time machines. When the time stream is altered, any changes are visible to the characters and happen with a "magic" effect and sound, and at the end of the game, the characters travel back in time to yesterday to turn off the machine that caused the Big Bad to become evil, thus causing a huge paradox and defeating the point of them even disembarking on their adventure in the first place. But that's okay. Doctor Edison's original plan (not taking into account the diamond breaking and the trio ending up in different eras) was for them to simply go back in time and turn off the aforementioned machine.
The game Second Sight plays with the trope. When John Vattic finds his way to the records room to find Jayne dead, he seems to flash back to the point when she is supposed to have died to save her, eliminating the reason he flashed back at all. This happens a few times in the game, to the point of Mind Screw. However, what's really happening is that the "past" the player is experiencing is, in fact, the present, and the "present" is a premonition caused by the protagonist's latent psychic powers emerging. It's pulled off extremely well.
The recent DS point-and-click adventure game Time Hollow suffers from this trope at times. At one point, you rescue a mother and son from dying in a bus crash. Immediately afterwards, time refuses to change. So you try again. And again, nothing happens. Turns out the mother deliberately RE-changed events to cause her and her son's death. This is handwaved with an explanation that objects and people pulled or otherwise sent through a time warp become 'detached' in time. It may make your head hurt a bit more when you are able to talk to the mother, older, in the timeline in which you saved her, even though that timeline, from your perspective, DOES NOT EXIST because she keeps changing the past to prevent it.
Timesplitters on the Gamecube and whatnot relied on Stable Time Loops for plot progression; for example, early on in the game Cortez receives a key after holding a conversation with himself through a grate in the ceiling ... then later, holds a conversation with himself through a grate in the floor and drops himself the key. And then in the game's conclusion, Cortez changes the past, stopping the Time Splitters from ever being created, complete with his Present being changed from a ruined battlefield to a beautiful landscape, with no real effect on him, or anyone else from his time.
This utter disregard for consistency is all worth it for the scene where Cortez is stuck in a vault with security systems trying to kill him, which the player plays through several times, thanks to the Stable Time Loops, and even gives himself the password, seemingly picking it out of thin air.
Tactics Ogre, despite its Chariot and Wheel of Fortune Tarots, averts this entirely. Although the World Tarot lets you relive the other chapter paths, thus opening up the possibility for a Timey Wimey Ball, the final events in Coda suggest that this is not time travel, but merely Denam's imagination.
Ingame, this is the home of the Bronze Dragonflight, Guardians of Time, which need the players' help against the Infinite Dragonflight which are trying to mess up the timeline. But really, it's just an excuse to let players reexperience some of the key moments in Warcraft history, although in a different way (instead of Thrall escaping captivity with the help of a human girl causing distractions, the players need to bail him out by force). If you screw up, the Bronze Dragons just hit the Reset Button until you get it right. The Doctor may have used the TARDIS for sightseeing, but the Bronze Dragonflight runs a travel agency.
And in patch 4.3, players get to travel back again, via the Caverns of Time, to the events in the War of the Ancients, to retrieve a magical artifact. However, the events of another novel are centered around said artifact, meaning they logically would be Ret Conned. Given that the events of that novel are what indirectly led to the rise of Deathwing, who is the main reason for recovering the artifact in the first place ... confusing doesn't even begin to describe it.
The existence of Murozond is one big Timey-Wimey Ball. At some unspecified point in the future, Nozdormu, Dragon Aspect of Time, will go insane and become Murozond, who creates the Infinite Dragonflight and wrecks havoc on the timeline with the goal of bringing about a Bad Future. Nozdormu himself is aware of this. He is also aware that this will lead to his death and that Murozond will ultimately fail to change anything, having both been granted a vision of his death by the Titans and personally witnessing it happen to his future self in the End Time. Murozond's dialogue in End Time implies he is indeed the same Nozdormu we interact with in the present day, and not an Alternate Timeline version of him, as he berates his younger self for "not know[ing]" his reasoning back then. Yet somehow, he still seems certain enough he will succeed to try and change the timeline anyway. But then Nozdormu loses his Aspect Powers in the Dragon Soul raid, which takes place after we're sent to the End Time but before Nozdormu becomes Murozond. Murozond does not seem to be weakened by this in End Time. Despite all this, Nozdormu is certain he will eventually become Murozond and there is nothing that can be done to stop it... Even though all he'd need to do to prevent it is not attempt to change something he already knows he'll fail to change if he tries.
Murozond was taken down by a 5-man group with some assistance from his past self. Malygos and Deathwing, meanwhile, required 25-man raid groups plus extensive backup. It's safe to say that Murozond was weakened by the whole depowering thing. Additionally, Nozdormu was told by the Titans that he must not change the circumstances of his death under any circumstances, so simply not doing anything that could turn him into Murozond is unacceptable.
Warlords of Draenor, the expansion pack announced at Blizz Con 2013, takes place in a Draenor heavily affected by the Timey-Wimey Ball. Garrosh escapes from prison, flees into the past of Draenor, stops the Orcs from drinking Mannoroth's blood, and introduces modern technology, creating a new "Iron Horde", changing the destiny of every major player on Draenor (and even the world itself). The only change to modern Azeroth, however, is that the Dark Portal changes from Green to Red, linking to the new Draenor, not Outland. How Azeroth is completely unaffected is thus far, unexplained (though one can assume Twisting Nether Timey-Wimey stuff.)
Word of God is that Garrosh traveled to a different timeline altogether.
The "Red Alert" series - seriously, the series by now has something in the range of 2 separate timelines from the first game, two from the second, two from that game's expansion, and then three from the third game, with a further three paths from THAT game's expansion. Even more brain-busting, Red Alert led to Tiberian Dawn by way of Allies winning both Red Alert 1 and 2 - Red Alert 3 is made by way as a divergence at the end of Red Alert 2.
Add to that the events of Yuri's Revenge which is its own separate divergence and has the nice consequence of there being two "commanders" (the player) in different places at the same point in the timeline. Also two Tanyas and two Lieutenant Evas.
One puzzle involves a time-travel maze where, at one point, you encounter your future self (and, later on, your past self, in exactly the same situation only controlling the other Guybrush). Taking an incorrect course of action (usually saying something wrong as the future self) creates a "paradox" that throws you back to the start of the maze. The puzzle goes a long way towards demonstrating the problems with a Stable Time Loop.
There's also the three items you get from your future self, and have to give to your past self. Where do they come from? Where do they go?
Even that's not correct anymore, because Sonic Generations centers around the Time Eater, a creature that can take places out of time. One of the places he takes, is Crisis City, the Bad Future version of 06's world. Even though, 06 never technically happened and shouldn't feasibly exist for the Time Eater to be able to access the events that happened in it, it somehow does, meaning that '06 does exist, but doesn't exist, simultaneously. Also, you play Crisis City where '06 fits in the timeline, not adjusting for the fact that Crisis City technically comes from a future that presumably took place well after the events of Unleashed and Colors. Fair enough, since Sonic first visited Crisis City in that order, but it still adds another layer of Timey Wimey to everything.
Shadow Hearts: Covenant: A Timey Wimey Ball in the good ending sends the main character back to the beginning of the first game with the implication that both of the first game's endings are canon. It also sent Karin back in time to meet Yuri's father and become Yuri's mother.
The activation of the god-golem Numidium in the conclusion of The Elder Scrolls II: Daggerfall allowed for several mutually-exclusive endings. The story-writers decided the simplest answer to this situation was for all of them to be true; the lore-writers followed suit. Cue the Dragonbreak, a moment in history where the Numidium's activation was so powerful it broke time. Time followed every possible path the player could follow, each time ending with Numidium's destruction... and then time snapped back together and every event became part of the new reality.
This has resulted in interesting paradoxes, including the existence of both the Worm God and Worm King, when they are both Mannimarco and should only be one or the other.
Generally, Dragon Breaks are closely related to the lore's concept of "Hero" (all Player Characters in the series are considered Heroes), an individual that is Immune to Fate, which allows the world's fate to continue despite the myriad ways the Hero can affect the game world (often in contradictory ways in different playthroughs).
Dragon Quest V has a literal Timey-Wimey Ball. As a child, your character finds a golden orb which doesn't seem too important. A bit later, you meet a stranger who asks you if he can have a look at it. At one point, the leader of an evil cult destroys the orb for no apparent reason at the time. After a timeskip and many hours of gameplay, your character, now an adult, finds out that the golden orb was really the power source of a floating castle. You then receive a fake golden orb, go back to the time of your childhood through a magic painting and secretly exchange the orbs with your younger self and return to the present with the real one, meaning that the cult leader only destroyed the fake.
Dragon Quest VII takes it Up to Eleven by centering the entire game around traveling to different times and places in order to restore the world... Good luck with keeping the different time lines straight.
Apollo Justice: Ace Attorney manages the difficult trick of pulling this off in a game that doesn't feature time travel. In the last episode, Phoenix's investigation as shown would not be possible unless he could actually travel through time, rather than being able to select different times just being a tool for the convenience of the Jury. He uses evidence he gathers in the present in the past, as well as evidence he gathers later in the same portion of the timeline in earlier incidents. Justified in that the Investigation you see is a simulated version being played out by the Jurists.
Ōkami manages this. First of all, you travel back in time to defeat Orochi with the help of Shiranui, your past self at full power, your grandfather, or yourself later in the game depending on your view of the Space Time Continuum. Next, Shiranui comes forward in time to help you beat the first part of the boss fight, only to get mortally injured in the present, then going back in time to die. Then, Chibiterasu, a son of Ammy, goes back in time to help his mom beat Orochi from nine months ago, thawing out his grandfather/mother at full power then going back in time 100 years in the past and... Yeah.
Back to the Future: The Game confuses the series' time travel mechanics even further, when Marty and Doc inadvertently create a timeline where Emmett Brown never creates the time machine in the first place (and in fact never becomes "Doc" Brown). While Marty is unaffected by the changes in the timeline (so long as it doesn't result in his erasure from existence, as usual), Doc actually disappears from the De Lorean once they land in 1985. The De Lorean doesn't start to disappear until Marty managed to get the 1931 timeline mostly straightened out, but only after another Doc Brown travelled back from 1986 to pick up Marty, and it took days for the thing to finally vanish.
Radiant Historia is all about using this trope, Tricked Out Time, and most other Time Travel Tropes in a quest to ensure the Golden Ending. The most confusing aspect is that while there are two separate timelines, making changes in one somehow influences the other, leading to things like helping someone recover from severe depression in one timeline so he won't try to kill you in the other one.
The Obvious Beta action-adventure game The Time Machine runs into a more literal version of this. Time is like a flat plane in the setting, and by travelling to the future, Wales causes his time and the future to become tied together by the time machine itself, pulling time together into a whirlpool of sorts that starts destroying time as he knows it. Which makes absolutely no physical sense, but serves to explain why returning to his previous time(and thus putting himself and the Time Machine back in the time where they belong) prevents any further damage to the time plane.
Despite only reading about the past rather than visiting it, Eternal Darkness uses a rather... unconventional form of this in the ending of the third play-through. Near the start of the first one, you picked one of three artifacts which would end up being the Big Bad. In the second play-through, that artifact was gone and you picked from the remainder; the ending was basically the same as if you had picked THAT artifact first, but the voice-over states that "something seems to remain". The third one was the same, leaving a single option; the third ending shows that all three events happened simultaneously, and were in fact the only way for Mantorok - the only even quasi-good member of a pantheon of four godlike beings that exist outside of time and space - to destroy his hideously evil counterparts. This opens up the New Game+ and allows for very satisfying cheats, but the ending in this final "joined together" timeline states that Mantorok itself is still sealed, rotting, scheming...
To say that this trope pops up in BioShock Infinite is like saying there's some water in the Atlantic Ocean. So you're hired to retrieve a girl from a floating city run by a racist madman who believes himself to be the American Jesus. Seems simple enough. Then you find out the girl can rend spacetime, go on trips to multiple time lines, find out the girl is the daughter you sold away in one possible world, and that the bad guy is a possible you.
The very first Ultima game has you stop the evil and immortal wizard Mondain by travelling abck in time and defeating him before he became immortal. Doing so should remove the centuries of tyranny and oppression from history, as well as cause a grandfather paradox (why would you go back to defeat Mondain if he was already defeated long ago?), yet everyone remembers everything.
Final Fantasy XIII-2 has a case of this once you get into the multiple time-streams. One specific example is that a solution to being trapped in an insane building by a computer trying to kill you is to scream at Hope, who is in the origin time-line in the distant future and will see the video and not turn on the insane computer.
Fire Emblem Awakening has some minor, weird cases of this. Midway through the game, you can start recruiting the main cast's future children, who all time-traveled to the point of the main quest. However, one of them ended up three years earlier than the rest of them for completely unexplained reasons, technically making him the oldest of the bunch. Plus, Morgan, the Avatar's child, is speculated to have come from a different timeline than the rest, which would have to be the case with some of the possible pairings (namely, if the Avatar marries a 2nd-gen character).
Dark Souls: The Player Character is told from the beginning that time in Lordran is inconsistent; everyone has their own "world" (i.e. timeline) wherein their own pasts and futures proceed in the standard way, but each of these worlds is technically separate from every other. Occasionally, two or more worlds can overlap temporarily and their inhabitants interact. The catalysts vary - people can leave messages for one another, including "Summoning Signs" that allow other travelers to request their aid, while other times these overlaps just occur naturally. Alternatively, certain "Orb" items can be used by players to invade other worlds to kill the hosts.
In Minty Fresh Adventure, Colgate can encounter Derpy, who's trying to deliver a letter to her, and the Doctor, who wants Colgate to not read said letter. The letter is Minuette's application for the position as a dentistry receptionist, from six months into the future, thus suggesting that Colgate will succeed in her quest to become a dentist. There are four endings depending which encounters you do; if you meet both, the Doctor will happily chide Derpy for nearly destroying all space and time just to give Colgate a little motivation.
There's No Time to Explain how time travel works before your future self gets grabbed by a monster and you have to go chasing after them.
Red vs. Blue starts out with a Stable Time Loop when Church keeps going back in time and ends up causing almost every problem that happened to the Blue Team. Then in season five, Wyoming uses his time travel ability (which Church was originally using without knowing it) to try and win the battle. Tucker has Ripple-Effect-Proof Memory thanks to his sword and they end up doing things, and then undoing them. For example, Caboose is killed by the tank, and Tex gets knocked out/killed by Wyoming. In the "final draft" of the timeline, Tucker yells at Caboose to stay away, and warns Tex that Wyoming knows that she's there. Then it turns back into Stable Time Loop when Caboose's mental image of Sister, who is a guy, gets pulled into the real world. S/he ends up materializing next to a dead Wyoming, whose suit malfunctions, sending him all the way back to Sidewinder. Turns out, he was the mysterious "Yellow Church" that fans speculated about for years.
Since the "Yellow Church" claimed his plan to solve the Sidewinder crisis "seemed like such a good idea at the time", it could be safe to speculate Sister/Yellow Church is there due to a further loop leading back to Sidewinder.
The series later attempts to explain all this earlier time-travel nonsense during the "Recollections" trilogy of seasons by explaining that the Red and Blue soldiers are actually simulation troopers meant to test Freelancer troops against a myriad of mad situations and everything they were subjected to in Blood Gulch was in fact a controlled situation they weren't meant to understand.
Actually Word of God from Burnie Burns has confirmed that Church going back in time repeatedly never really happened, and was merely Gamma and Omega trying to cause Alpha to fracture into more A.I. fragments. Nobody moved through time in season 3. Yes this is a major retcon, but as of Season 8 it is considered the canonical explanation.
In Bob and George most of the characters can never find out what kind of rule Time Travel goes by, and one person once said it can be changed by the setting on the time machine. However, it appears that they follow Stable Time Loop rules, as no time period is ever affected by what happens in another. Indeed, the only way time travel is different than going to a different dimesion is that people think it may change history.
Dr. Light's lab is clearly shown being pre-destroyed by a time ripple tearing through it and enforcing events from the new past. So yes, the past can be changed if you use the time machine right.
The ending however, suggest a stable time-loop, as it ends with a suggestion from a time-travelling ghost of Zero telling Wily to not activate him so he won't kill everyone. Then they all fake their death and move to Acapulco to prevent a temporal paradox.
There is a very good reason why "I hate Time Travel," is one of the more common Catch Phrases of the comic.
At another point, Protoman adds a fresh level of murk due to a) lacking Ripple-Effect-Proof Memory and b) being paranoid enough to know he lacks Ripple-Effect-Proof Memory, by remarking that a time-travel story is exactly how he remembered the events in question...well, it's how he remembers it now.
Looking for Group has a big fat temporal loop in the Kethenecia arc in Book 3, but really the arc underlies the whole story so far. It's still uncertain if the protagonists can actually change the timeline should they chose to, since so far they did their best to fulfill the prophecies.
The webcomic features an extended time-travel subplot which establishes that it is difficult, but not impossible, to change your own history. Physical time-travel takes all the energy that exists in the Universe or, as it turns out, in some other universe that's just out of luck, but it's possible to transfer your consciousness back or forward in time into your own body, and you can undergo changes as a result of altered behavior. For instance, Dave never smoked. At several points, the question of paradoxes comes up, and it is immediately dismissed by pointing out that thinking about it could cause it to happen, so it's better not to.
The same storyline provides an example of inconsistent time travel effects within a single sub-plot. Dave didn't cease to have ever smoked until after the time travel; however, Caliban's demotion, though also caused by the time travel, was established backstory before the time travel occured.
Time travel in Irregular Webcomic! at first appears to work in a Stable Time Loop fashion, but then it's revealed that It's possible to "break" a Stable Time Loop, an action capable of destroying the entire universe.Several time loops have already been broken. And now Every universe, save the "espionage" theme universe, has been destroyed. They got better.And now apparently the timeline is too broken to go back pre-1933 (specifically the date of the Reichstag Fire). Complete with a link to this very article.
This page of the Midnight Crew intermission in Homestuck typifies the response. Though most of the time travel shenanigans seem fairly self-consistent, it's still hella complex.
In the main continuity of the series, it gets worse when Future!Dave starts incorporating Time Travel shenanigans. And even he doesn't understand all the mechanisms behind it, his advice to the other characters (and the audience) is just basically "Don't overthink it."
Dave: see the thing with time travel is Dave: you cant overthink it Dave: you just got to roll with it and see what happens Dave: and above all try not to do anything retarded John: i'm just the timey-wimey messenger here.
However, Magic A Is Magic A applies heavily and every form of time travel is internally consistent. The problem arises when there are at least four different forms of time travel, and possibly even more, all of which abide different rules
Heroes of Time have two options. Either A) They change destiny and cause a branch timeline, or B) You Already Changed The Past. They naturally have some intuition about what changes cause what. Time magic practiced by the Felt is more loose, and can be used for pretty much any form of Time Travel. And then there's the weird stuff, like the Furthest Ring distorting space and time, potentially causing someone to meet their past selves by traveling in a straight line and Skaian portals.
Imagine four balls on the edge of a cliff. Say a direct copy of the ball nearest the cliff is sent to the back of the line of balls and takes the place of the first ball. The formerly first ball becomes the second, the second becomes the third, and the fourth falls off the cliff. Time works the same way.
This is probably gonna be the only way to understand the whole time traveling bit in Sonichu. To wit, Author Avatar Chris is launched into the future where he is able to help those in the future make the vaccine for homosexuality (even if that's not how it works) before being able to convince his future wife Lovely Weather he is his future self (despite the fact that he'd be ten or so years older) and do the nasty. He comes back, gives Magi-Chan Sonichu a Sonichu Ball and tells him to go back and get some of the vaccine to bring back to the past so they can cure everyone years earlier. And while he does talk to the past version of Lovely Weather, there's the case of the vaccine - if he brought the vaccine back from the past to cure everyone, why would there be a need for it in the future and oh, going crosseyed.
There don't seem to be any concrete rules to Sluggy FreelanceTime Travel. Possibly justified by the presence of beings like Father Time, Uncle Time, and the Fate Spiders who have an interest in making sure time runs smoothly and/or in a fun way.
The fact that the original fate spider gives up, quits his job and then only comes back after his successor has screwed everything up even more says a lot, at this point they seem to pretty much just watch and be amazed that all of creation hasn't gone up in flames already.
In a more recent strip, Old-Riff says that Time Travel follows the branching timeline rules, and therefore you can't change the past, you're just abandoning the Bad Future in favor of a different universe. But really, the way it works, this revelation doesn't actually contradict anything, since from the characters' perspective, they would have no way of knowing.
The robot Gizmo goes back in time to kill Hitler, reasoning that he can then go back again and stop himself. Instead, his first iteration convinces him to join in, since he can just go back again, and stop himself. Predictably, they end up having dozens of Gizmos brutalizing Hitler before he's had enough and stops his first self... and gives him a video recording of the event.
In another chapter, Gizmo went insane from a virus while saving the ship. The other crewmembers fix this by taking his head off (it contains his processors and memory drives), going back in time to just before he went insane, and switching heads, thus bringing his sane head back to the present while the insane one faces the virus (presumably, he can't go even insaner).
Used to great effect in The 10 Doctors. It's even mentioned by name as to how all ten Doctors can be in one place at the same time.
Third Doctor: You see... time is... well... it's... Second Doctor: Well, it's... It's not linear... It is more sort of... Tenth Doctor: It's... squishy-squashy... Seventh Doctor: Wibbly wobbly. Sixth Doctor: Semi-fluid! Fifth Doctor: Gelatinous. Ninth Doctor: Mushy-gooey. Drax: Higgledy piggledy. Fourth Doctor: Hi-ho the dairy-o! Romana II: Green grow the rushes-o! First Doctor: Alright, you lot!
The sequel fic Forever Janette intentionally invokes the Timey Wimey Ball by subverting the show's use of San Dimas Time — by letting the Fifth Doctor meet the Master from the Seventh Doctor's time. It doesn't say how this is possible, other than a passing mention that the two Time Lords are "off-phase" from a common Gallifreyan synchronicity.
Manly Guys Doing Manly Things heavily lampshades this trope. The main requirement to avoid the variety of paradoxes is "Don't think about time travel".
Mind My Gap is a plot made of this. It seem at one point that up to four chronologically separate events with the same characters involved are happening at exactly the same time
Phaeton has time travel mechanics, but also has laws, and etiquette, all to prevent this from happening. Still there are people who don't follow the "Six Minute Flux" mechanic and cause this.
According to Huey in Ducktalez 5, the time-travelling Deweys all come from alternate timelines that are created when one of them tries to change history. Huey offers a situation, but that fails. Also, Dewey tries to ask for the Doctor's help, but that fails.
There's a gigantic lampshade in Tripping the Rift. The crew saves the day by turning back time Superham-style: by flying the ship around a star counterclockwise really fast. While they're setting up, they discuss the inconsistency of the rules of time travel and the problems with changing the past.
In the double-episode "Two futures" of Captain Planet and the Planeteers, Wheeler uses a time pool to go back and prevent himself from receiving the fire ring. This results in a crapsack future because the Planeteers never became a team and saved the environment (though why they didn't just find another guy to accept it is never explained). He then goes back and prevents himself from preventing himself from getting the ring. Then they both escape into the time pool again and merge for some reason. To make sure the viewers knew things were restored to normal, a scene from the utopian future is shown at the very end.
The plot of a Pinky and the Brain episode, in which the mice try to obtain a "World Domination Kit" from the future. It doesn't even try to make sense, but suffice to say it ended with the lab full of hundreds of Pinkys and Brains, and the ending tune changed to "They're Pinkys, they're Pinkys and the Brain Brain Brain Brain Brain Brain Brain Brain Brain Brain."
This episode of Tek Jansen, a series of shorts originally created for Stephen Colbert's show, illustrates how bad (or awesome) this trope can get.
After Thrust shoots Starscream with the Requiem Blaster, we see a shot of Rad as an eight year old waking up in his parents' car and asking tiredly where the Mini-Cons are (implying his "present" mind was momentarily in his past body). Then cut to all the kids - possibly in an alternate future - being told by a slowly dying Hot Shot that the Transformers have all been eaten by Unicron because they didn't know that the Mini-Cons were servants of Unicron and were led to their doom. After this, cut to the kids now being at the moment of the Mini-Cons' creation millions of years ago inside Unicron. Rad then touches High Wire's hand and frees him (and by assocation all the other Mini-Cons) from Unicron's control by reminding them of their past/future happiness together. The Mini-Cons then know to go to Earth after they leave Cybertron to meet Rad and the other humans. Cut back to the humans returning mere moments before Thrust shoots Starscream, whereupon High Wire and his teammates combine into Perceptor and knocks the gun away, causing Thrust to miss Starscream completely. And none of this is EVER EXPLAINED.
The Mini-cons who prevented Starscream from being blastedweren't taken along with the kids' inexplicable time-jump, and there is no reason for them to have done anything differently in the present. It can't even be due to the kids' actions in the past — the Mini-cons would never have gone to Earth to kick off the events of the series if not for the kids, so it's not a case of the "old" High Wire wanting Starscream to die but the "new" one saving him.
One of the first episodes of Sealab 2021 shows Stormy and Quinn trying to steal cable for Captain Murphy and inadvertently cause a rift that sends them back in time to just before they left Sealab (about 15 minutes). They try to prevent themselves from causing the rift, but past Stormy and Quinn capture future Stormy and Quinn and lock them up in the gym while they're gone, where they remain when the next pair causes the rift. Since the time difference is only 15 minutes, each successive Stormy and Quinn react in the same way, and since each pair is unable to stop the next pair, the number of Stormies and Quinns keeps growing until the gym is filled with them, each pair a slightly malformed copy of the previous pair. Eventually, it takes all the Quinns working together to figure out a solution to the growing problem, and all the Stormies play dodgeball. Also, Stormy having a communicator watch.
Time travel results in the creation of Stable Time Loops... except when it doesn't. In "Roswell That Ends Well", You Already Changed The Past is in effect, and everything makes sense. Then "The Why of Fry" contradicts this, and Fry succeeds in altering his own past (he doesn't prevent himself from getting cryogenically frozen, as he originally intended, but he does convince the Nibblonians to give him a better getaway scooter). Then, Bender's Big Score throws sense out the window: Bender's rampant time travel is revealed as the cause of some events from previous episodes (such as the fossilization of Seymour, and the first destruction of Old New York by flying saucers), while completely altering some other events (the final scene of "Jurassic Bark" gets retconned). Both stable time loops (like the tattoo on Fry's butt) and utter nonsense (like Hermes Conrad stealing his own body from the past) work equally well. Rather appropriately, Bender's time travel is carried out by a literal timey wimey ball.
Then there's Professor Farnsworth's time machine in "The Late Philip J. Fry", which could only go forward in time. When Farnsworth, Fry and Bender returned to a new, identical universe (making the Big Bounce theory true) It's impossible to know if the killing of the fish or Hitler did anything to Universe Two because they didn't get to stop in the 31st century to find out. They had to go around again to finally make a stop at Universe 3. This leads to all sorts of crazy implications as to what happened to the time traveling crew in the 2nd universe...do they kill their Universe 4 selves?
On the DVD commentary for "Roswell," the writers say that they initially intended to avoid doing any time travel stories, because it's basically impossible to make them make sense, but eventually they couldn't resist.
Time travel in The Fairly Oddparents is... confusing. The first time Time Travel is used as a plot device, and in most subsequent appearances, history is very malleable and can easily be changed... with serious consequences.
However, the episode "The Secret Origin of Denzel Crocker" appears to utilize a straight Stable Time Loop... however Timmy's time traveling, in addition to causing Crocker to lose his fairies as a kid, also gave him a much more sophisticated fairy-tracker which he didn't originally have as an adult, meaning that Crocker must have lost his fairies a slightly different way the "first time around".
In a much later episode when Timmy wishes he were never born, a laIt's a Wonderful Life, Jorgen reveals that Crocker's childhood would never have been ruined had Timmy never existed, which means that there was no "first time around" note if there were, one would expect that Timmy negating his own existence would have undone all his changes to the past and history would be restored to the way it originally proceeded, sans Timmy of course. In other words, the writers wanted to use both Stable Time Loops and Temporal Paradoxes at the same time, resulting in a confusing mess. Cosmo did a lot to get little Crocker obsessed with fairies, but he only got the opportunity due to Timmy.
The first time they time-travel also brings up a lot of questions. The Time Scooter and Laser Eyes still frequently make an appearance whenever Timmy needs wishes that he never unwished. But that entire episode contradicts everything else, such as Cosmo and Wanda being Bill Gates's Godparents (at the time, they should have been Crocker's parents) and the appearance of Timmy's Dad. Depending on the version, Mr Turner either met Dinkleberg when they were children, or didn't even know about the couple until they moved next door.
Time Squad, for a show aboutTime Police, has some of the worst time travel logic ever. The premise itself of how the past "unravels" as time moves on would make The Doctor tear his hair out.
The Penguins of Madagascar has Kowalski try to stop two paradoxes that he created at the same time. While it's eventually resolved with a stable time loop, the second/third Kowalski couldn't have existed without having it's own paradox. It's... confusing. And the paradoxes effect time is only a few hours.
In an episode of South Park, Cartman freezes himself and is thawed out 500 years in the future. He then makes repeated calls to Kyle via a phone that reaches back through time, which makes changes to his time. He and everyone else 500 years from now only know the world the way it is after the changes. However, when he makes one more change at the end that hugely impacts history, he only remembers what the world was like before the change, while from everyone else's point of view it's always been that way.
In X-Men, Bishop keeps his memories of the previous chain of events when he returns into the future. Later the two parter "One Man's Worth" has the death of Charles Xavier before he founded X-Men resulting into a war-torn present. Wolverine and Storm from this changed reality travel into the past to help to save him. After the successful mission accomplishment they return into the future (present time) and for some reason lose all their memories about the Xavier-less reality.
In the Adventures of Sonic the Hedgehog multi-parter Scratch and Grounder made it so a couple of Sonic's ancestors didn't meet, making Sonic disappear. But for some reason Tails is still there and able to fix this.
Randy Cunningham: 9th Grade Ninja: When the past was altered so the Sorcerer's imprisonment never happened, it got the Sorcerer free but didn't change the world in any way that reflected the damages he would have caused during eight centuries of altered history. No explanations were given.