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Some authors plan meticulously. Before they even start to write, they have a detailed plot synopsis, character biographies, pages on setting, and a detailed backstory to the main tale... at the least.
Others just sit down at their word processor and type whatever comes into their head. This trope is dedicated to them.
This is not necessarily a trope about authors who simply write without a speck of planning at all (although it can be), but rather those who, overall, are improvising as they write. They may already have invented their characters, perhaps they have a vague plot bubbling in their head, even a few notes on backstory or setting. What separates this kind of writing from planned writing is that these writers are prepared to throw those notes in the trash the moment they come up with an idea that they prefer. So you're writing a hardboiled crime fiction novel: Remember that takeaway place you thought up on the spot to give your sleuth somewhere to eat his lunch? That would be perfect as a front for the Big Bad's drug-dealing business. Making a movie? That actor's take on that character is way better than what you originally had in mind. Why not rewrite half his part to take advantage of that vision?
The trope name comes from the phrase "flying by the seat of your pants", a colloquialism for "deciding a course of action as you go along".
Like most things, this can be done well, or badly. The Chris Carter Effect and Kudzu Plot is what happens when Writing by the Seat of Your Pants leaves too many loose plot threads.
This is the novelistic version of Schr÷dinger's Gun or the Indy Ploy; when the author of a series canonizes fan suggestions as he goes along, see Ascended Fanon. Can also be related to I Just Write the Thing.
Please only add examples where the author admitted to doing this. This is not a page for speculation.
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Writer Tsugumi Ohba admitted that this was pretty much the way theynote They keep their identity a secret, which includes their gender wrote Death Note: they'd write Light into a massive jam at the end of one chapter, and would then try and figure out how to get him out of it only when time came to write the next one.
Bleach: Tite Kubo has admitted to using a combination of this and arc planning. However, he is infamous for using this trope and for his special use of Chandler's Law: "When suffering writer's block, introduce a new awesome character to overcome it". The trouble is, he doesn't actually introduce a new character, he introduces a new Cast Herd instead. Loads and Loads of Characters ensue.
Hidenori Kusaka does this in regards of PokÚmon Special, as he has to write along side of whatever games just come out. What really makes him impressive, however, is that he doesn't work for Game Freak yet the series has a sheer amount of generation-spanning Arc Welding and Chekhov's Guns. Fans joke that he can see into the future.
Osamu Tezuka wrote Ambassador Atom (the prototype for Astro Boy) as he went along. Notably, he had no idea who "Atom" would be, until he later decided to write him as a robot built to replace Tenma's deceased son. He would later Re Tool Atom into his current incarnation, and subsequently redid the story as an episode of Astro Boy.
Rumiko Takahashi admitted not planning and not knowing where her manga was going during the supposedly final battle with Naraku in InuYasha or with Rinne in general.
Much like its initial influence Fist of the North Star, Hirohiko Araki has admitted that he's been essentially making up JoJo's Bizarre Adventure as he goes. While this is impressive in that the story likes to make a lot of call backs, it does explain the more "villain of the week" format that was in much of parts 3-5.
The original writers of Impulse admitted they were writing by the seat of their pants in the first trade. Given the character, this is quite appropriate.
Prolific comic book writer Robert Kanigher did this all the time. The results run the full gamut from enduring classics to ludicrous dross (but it was ludicrous dross that was handed in on time, and that was the important thing). Among other things, he was prone to recycling plot details, particularly from earlier issues of the same comic. To be fair to Kanigher, he had a very large monthly workload throughout his career, writing as many as seven comics each month and serving as editor for most of them.
Compare "The Marvel Method" from the same era: One writer would plot a story, an artist would draw the comic, then another writer would do the dialogue, often having to explain things all by himself. This is why Marvel was able to put about half a dozen or so comics each month even though the stories were devised almost exclusively by Stan Lee, Jack Kirby and Steve Ditko. Marvel used this system as late as the 80's.
Chester Gould, the creator of Dick Tracy, made up his stories as he went along. His maxim was that if even he didn't know where a story was going at the start, then his readers certainly wouldn't be able to guess.
Though once he forced himself into a corner that he, at first glance, could only solve by having the eponymously named Dick Tracy tell Chester Gould to get him out of this situation and a giant hand erased the death trap. The news editor found it stupid so he told Gould to find another solution.
Judge Dredd creator John Wagner has said this is the way he prefers to write. Case in point: the reappearance of the Dark Judged in "Day of Chaos" wasn't originally planned, but with all that was going on in Mega-City One at the time, bringing them back was the perfect way to make things even worse.
The revelation in New Avengers that the Ronin was Maya Lopez in disguise was a last-minute change after the original plan (where Ronin would have been revealed revealed to be Matt Murdock) fell through.
This is rather evident from the fact that there is nothing even slightly androgynous about Ronin's very buff, masculine build — and then he takes off his mask and s/he's now a typically beautiful comic book woman.
Herge said that this was how he worked on Tintin at the beginning of its life. He needed a new installment each Thursday and said that he often found himself working on it on Wednesday, not knowing how he'd get Tintin out of the mess he left him in last Thursday. He stopped doing this with The Blue Lotus and started plotting things out more fully.
How the first Yognapped was written. It was first set as though Simon Lane and Lewis Brindley of the Yogscast's real-life counterparts were playing Minecraft and commentating, but moved on to an actual post-Shadow of Israphel universe with the characters of Simon and Lewis' Minecraft avatars, alternating in-between for several chapters before settling on the latter. This led to some plot holes that the writer has attempted to Retcon, with varying degrees of success.
The creator of Origin Story admits that, while he began with a carefully plotted outline, the story left the outline in the dust in the middle of Chapter Four and that these days, he's writing whatever comes to him to write, as it occurs to him to write it. That said, he's still managed to put together an intricately constructed and emotionally engaging story, and it absolutely does not look like he's been improvising for the majority of the story.
According to the book The Disaster Artist, everything that fans love about The Room was ab libbed. Tommy Wiseau was writing, directing, casting, rewriting, and acting by the seat of his pants, practically making up the film as he went.
Casablanca was being written as it was filmed. Some things had to be changed to comply with The Hays Code, and it took a while to come up with a satisfying ending.
In Iron Man, the actors came up with so many good things on-set that halfway through they just threw away the script (having previously rewritten it every night) and instead wrote outlines of each scene instead. Jeff Bridges said that it felt weird doing it this way, then realized that he had to treat it "like a 200 million dollar student film".
Tim Burton's Batman was constantly being expanded, edited and rewritten. Burton himself once recounted a situation wherein he had The Joker take Vicki Vale hostage and move into the Church, with no idea what to do storywise after that point.
The 90's movie of The Fugitive was largely made this way, on the fly—although one would never suspect by watching it, as it looks very carefully planned.
The Lord of the Rings movie trilogy was shot like that. Even as the cameras kept rolling, scenes and plots were being rewritten again and again - some versions of the script reached not just the double digits, but went up to 40 and above. Actors frequently got their lines only at the night before the shooting and major revisions resulted in whole scenes being re-shot. Ironically, the writers insist that each iteration was ultimately closer to Tolkien's work and even stated that some of the remaining controversial changes might have been gone too, had they not reached a deadline by then.
Befitting its chaotic production schedule, Apocalypse Now was made largely with this and Throw It In. Francis Ford Coppola didn't even have an ending, as he'd considered John Milius's ending (Willard joins Kurtz, and the film ends with Kurtz shooting at American war planes bombing his temple while screaming about his erection) ridiculous.
Scanners was written like this, which was forced upon David Cronenberg because of the way the production had to be structured due to financing reasons. There was virtually no pre-production, so he had to start shooting with an unfinished script. He would write in the morning, and film the rest of the day, mostly out of order. On top of that, they often had to drive around at random, looking for places to shoot scenes. So literally everything about Scanners was done by the seat of their pants. He talks about it at some length in Cronenberg on Cronenberg.
Stranger Than Fiction has an in-universe example. We see Karen Eiffel writing Death and Taxes while she's still trying to figure out the ending.
Lawrence of Arabia. Shooting was just about to start when David Lean threw out Michael Wilson's original script completely. Robert Bolt was brought on to rewrite the script as filming began. As a result, the movie was filmed almost chronologically - a rarity then or indeed now, especially on such a large-scale film.
An excellent summation of this trope from E L Doctorow: "It's like driving a car at night. You never see further than your headlights, but you can make the whole journey that way." (also quoted by Anne Lamott).
There's a famous Bradbury quote on his method of writing that pretty eloquently sums up this trope: "You've got to jump off cliffs all the time and build your wings on the way down."
Isaac Asimov was on record stating that, while he usually had an end in mind, he almost never had any idea how he'd get there.
Garth Nix says this is how he writes - most of his world building is made up on the spot.
Stephen King falls into this category — he never plans ahead, he just writes until he has a good idea and runs with it.
The Green Mile may be his best example of this. It was originally released in installments. At the time the first installment was released to the public, he hadn't even figured out the ending yet... but still a set release scheduled for it.
King said in On Writing that he does occasionally plot his stories, he just does it rarely because he usually isn't proud of the results (like Rose Madder and Insomnia) when he does—with one exception: The Dead Zone.
The NaNoWriMo project lends itself to this approach. Participants are given 30 days to see if they can write at least 50,000 words. note Not all NaNoWriMo writers write by the seat of their pants. The rules allow writers to have character sketches, plot summaries, and even extensive, detailed outlines — as long as none of the actual prose is written before 12:00 AM on November 1.
The Reverend Lionel Fanthorpe churned out novels for Badger Books on the basis of a book cover, a title and a very short deadline. Badger's policies mean it's impossible to tell exactly how many he wrote, but the estimate works out at one 158 page book every twelve days. To manage this, he dictated into a reel to reel tape recorder, then shipped the tapes off to a pool of typists for transcription. To hit the word target, he would pad out the books with philosophical discussions, mundane detail and redundant descriptions (robots: "Metal things. Metal things that could think. Thinking metal things"), but then could be told that he had only three pages left to wrap up the story, so he had to pull out a Deus ex Machina. Despite, or perhaps because of all this, Fanthorpe's work has picked up a So Bad, It's Good following.
L. Ron Hubbard claims he wrote by meditating into a trance-like state and typing constantly for hours at a time. According to Harlan Ellison, Hubbard used the Jack Kerouac method — he rigged a roll of butcher paper of the appropriate width to feed into his typewriter, wrote for several hours, and at the end cut the long sheet down into even pages.
Douglas Adams wrote The Hitchhiker's Guide to the Galaxy this way largely - throw out tons of ideas, then return later when it seems like one of them is funny or could be made relevant (like the potted plant saying "Oh no, not again"). As you can imagine, Adams was terrible at deadlines and finished the first book at that page because his publisher was furious. He once remarked, "Writing is easy. You just stare at a blank page until your forehead starts to bleed."
Robert B. Parker of the Spenser, Sunny Randall and Jesse Stone series wrote like this, and compared it to being like the detectives of his novels never knowing what was coming next.
Horace Kelton once replied to a friend that he didn't know "what [his] next book would be about. The characters [hadn't] told [him]." But he still planned some once he got the basic idea.
Charles de Lint writes that way and refers to it as an "organic" style of writing.
Terry Pratchett usually writes with a plan, but in an interview said that while writing the assassin's "driving test" in Pyramids, he had absolutely no idea how it would unfold, and consequently it is one of his most favorite moments in the Discworld series.
When he sat down to write Guards! Guards! he intended for Carrot Ironfounderson to be the main character, with Samuel Vimes being a minor character who was there to provide a viewpoint character in the city before Carrot arrived. As he wrote the novel Vimes took over as the main character.
Hunter S. Thompson not only did this, he made it the essence of Gonzo journalism: Your notes, more or less unedited, are the finished product. He would frequently spend hours or days locked up in his room with a typewriter, a whole bunch of paper, and half a ton of drugs and booze, hammering away furiously to send a long, rambling, yet somehow incredibly cogent piece off to Rolling Stone or whatever other publication he was writing for at the time. He famously declared his most famous work, Fear and Loathing in Las Vegas to be a failed experiment in Gonzo journalism, as he had edited it too much.
Ellen Potter, author of The Kneebone Boy, had no idea how it would end when she wrote it and was, at her own admission, stuck on the ending for months until writing something that came to her at the gym. Unfortunately, a lot of plot threads are left dangling as a result.
The 20th Anniversary Edition of Timothy Zahn's Heir to the Empire has a lot of notes in the margins, which reveal that the book changed a lot during the process from first draft/outline to completed manuscript. Most big ideas were set early on, but small details seem to have come spontaneously, like Luke drinking hot chocolate. He also threw in a consistently varied selection of cryptic side references, mostly used to make the galaxy feel bigger, like the films did. Later many of these were picked up in order to perform some remarkable feats of Arc Welding - but as he notes while explaining,
Still, don't let all these clever explanations give you the impression that I had this whole immense thing mapped out in advance. Right now, I'm using the Indiana Jones approach, and making it up as I go.
George RR Martin describes the technique like taking a road trip. You know the broad strokes of the trip—where you start and where you end, and maybe some of the major roads you'll be driving along the way. But you don't know what diner you'll be eating at on day three; you don't know about the construction on the I-95; you don't know that you'll stop at a tourist trap you didn't even know existed during the detour...
Calum P Cameron apparently writes the Mediochre Q Seth Series by formulating a basic plan, typing until he gets stuck, then walking his pet dog until he spontaneously comes up with enough new scenes to start typing again. Or he did, until the dog died. Presumably he still adheres to the trope, though, just without the dog-walking bit.
The authors of Animorphs had no plans at all for the overarching plot going in - they came up with a plot synopsis before each book, but beyond that, they didn't have a clue. (The one exception seems to be their knowing ahead of time that Rachel would die at the end.)
An variant of this trope is when the author lets dice (or any random generator) decide over the plot. "Paradise of Swords" by Tobias Mei▀ner is a good example - almost an RPG-as-book. Probably better known is "Il castello dei destini incrociati" by Italo Calvino.
In the original KTMA season of Mystery Science Theater 3000, the riffs were improvised rather than written. The films being mocked hadn't even been seen in their entirety in advance. In the Comedy Central era, however, each film was carefully screened and written for before its respective episode was recorded. The show became better for it.
During the first season, movies weren't watched in their entirety until the actual writing process took place. They changed to pre-screening the whole film after viewing the violent rape scene in The Sidehackers.
Battlestar Galactica (Reimagined). The writers' commentary on the DVD makes it clear that a lot of stuff was made up episode-by-episode. Especially irritating when every episode began with the statement "... and they have a plan." Many viewers found this especially apparent in the plot points involving the identity of the Final Five cylons, leading to images like this one◊. It really came back to bite them when they decided that the "Final Five" Cylons should be different than the others, and have the last five model numbers. Trouble was, it had been built in the show from the start that there were twelve models, and they'd already given one of them the number Eight. So the writers had to quickly insert a piece of backstory that another model had been judged so corrupted (read: wanting to be human) that all copies were destroyed permanently.
Another issue this caused was that Tyrol was made one of the Final Five despite having a son, due to the writers forgetting that Cylons couldn't have children. When they realized this halfway through the final season, it was quickly retconned that his son with Cally was actually the result of Cally having a one night stand with Hot Dog the night before they began dating. And then the episode wasn't quite as clear as it could have been that this was what happened, leaving many fans with the impression that Cally (now long dead and unable to defend herself) had cheated on Tyrol.
The series has many examples of Throw It In and such but the identity of the killer wasn't meant to be revealed in the first place and happened only because of Executive Meddling. This, of course, doesn't make it any less this trope, or rather it could be considered even better example.
After revealing who killed Laura Palmer they didn't have a clear idea how to keep Agent Cooper in the series, and with Lynch busy on over projects, the writers struggled throughout series two for the show to have a focus.
The vast majority of soaps work on this principle. It's essentially the nature of doing a work "live." Real Life Writes the Plot sometimes contributes to this trope, especially for things like pregnancies.
Parodied in a Kids in the Hall sketch, which warns the viewer that it was "written in haste," showing the writer frantically mashing a keyboard trying to finish it within the deadline. The scene is filled with nonsensical actions and garbled dialogue caused by the typos, such as a man taking off his "rubber boobs" and sitting down on a "chain."
Aaron Sorkin does this. There's a story that when he was writing The West Wing, he needed President Bartlet to be lying in bed for a scene — and so gave the character multiple sclerosis.
Many committee-led series will change plot and emphasise characters depending on audience responses to broadcast episodes. Sylar and Hiro in Heroes received such a favourable response they were given much larger roles in the long run including Sylar being allowed to live beyond the Season 1 finale.
The writers of Glee seem to be really, very, extremely guilty of this, partially because of their fondness for Pandering to the Fanbase and partially because they think of the show as a "pop-culture tribute" and basically just write around whatever's currently popular or of note in some way. And they also just change their minds a lot, like when Ryan Murphy broke up Quinn and Sam because he "got bored" with them. Overall, this keeps the humor of the show extremely up-to-date and relevant, but it also leads to many, many out-of-character moments that some viewers find annoying.
The series finale of The Prisoner was written in a trailer over a weekend. Not surprising that it's one of the most infamous Mind Screws in television history.
24 was notoriously written on the fly, with the writers starting each season with practically no concrete idea where the thing was going to end up. Notably averted by Season 7, due to the 2007 Writers Strike and a year-long delay, resulting in a much more cohesive, planned-out storyline for that season.
Doctor Who, partly by necessity. While an individual head-writer/producer might have individual plans, the show's Long Runner status means that this is a little bit necessary. For example, a lot of the things that have made the show so iconic, such as The Nth Doctor trope or the Daleks, weren't planned, but added as they went along.
The creators of The Big Bang Theory have commented that every season they start with simply the next page. Chuck Lorre apparently has a motto that "This isn't LOST" and thus they keep everything in the moment and not holding out based on what they have planned. Although looking back it would be easy to believe they did plan out at least a season in advance, given the progression of Leonard and Penny's relationship in the first two seasons and how Howard started to mature in the second season which allows him to start a relationship with Bernadette in the third.
The famous cliffhanger at the end of The Best of Both Worlds, Part I was due to the Star Trek TNG writers not knowing if Patrick Stewart would return as Picard or not, forcing them to pause there and then write Part II by the seat of the pants once they found out about Stewart.
NYPD Blue was often written on set during filming due to head writer David Milch's drug use. "OK, you [Sipowitz] say this, and then you [Simone] say this in response." Actors wrote down their lines on scraps of paper in the squad room. Jimmy Smits and other actors quit over the hectic scheduling.
How I Met Your Mother starts with a Driving Question of "How does Ted meet the future mother of his children?" and the creators were adamant that it would happen in the Grand Finale. The thing is they weren't sure how long they would get to tell this story and there are several admitted plans in place in case they were or were not renewed. Victoria of season one was outright confirmed to be the Mother in case the initial 13 episode order was all they had. Stella is theorized to also be a back-up Mother (given how they meet ties directly into the implied "Myth Arc") if season three was the end. Once ratings stabilized it seemed that the writers had a clear idea of how the show would end by introducing some more solid clues (the 100th episode has Ted meeting the Mother's roommate and getting a lot of, still vague, information on her) but still had to keep things flexible because now they weren't sure when they were ending.
LOST's pilot and first six episodes were written with only the vaguest of long-term planning (i.e. "Locke will find a hatch sometime, and there's a science compound, and maybe we'll reveal two gods were playing a game the whole time.") because Damon Lindelof admitted he didn't think the show would last. He just cribbed the flashback structure from Watchmen and wrote whatever interested him while waiting for the cancellation notice. However, when the ratings came in, he teared up in exasperation and asked, "You mean we have to keep doing this every week?!" He put in a call to his old boss, Carlton Cuse, who came onboard after "Confidence Man" and helped him sketch out a very rough outline, but they soldiered through the rest of the first season by ad-libbing it, including the infamous "numbers". It wasn't until the summer break that they spent a month planning out the rest of the Myth Arc.
Lampshaded in a "Weekend Update" skit from Saturday Night Live, where Amy Poehler reported that Lost had been renewed for another two seasons.
Poehler: When reached for comment, the writers of Lost said: "Crap."
The entire concept of "jamming": musicians will spontaneously come up with music to match an overarching, usually repetitive, tune going off of nothing more than their instinctive abilities.
Elvis Costello recorded the album Momofuku in six days. He joked that "the record was made so quickly that I didn't even tell myself about it for a couple weeks."
David Bowie's preferred methodology of song writing. Tony Visconti, his long time producer, has confirmed that Bowie will often come to the studio with just a few chord changes and write the lyrics and vocal melodies on the hoof.
Notably, his #1 hit collaboration with Queen, "Under Pressure" was the result of a single night spent jamming with them - which was very different to the usual manner in which Queen made music.
Post-Rock band Mogwai's first full length album, Mogwai Young Team, contains 10 songs, only 3 of which had been written before the album's recording sessions began.
Songwriter Rod Temperton, who composed Michael Jackson's hit "Thriller", wrote Vincent Price's spoken-work portion of the song mere hours before the recording session began!
In pro wrestling jargon this trope is referred to as "hotshot booking" or "hotshotting." While there are many examples of hotshotting in the industry, one of the more famous occasions was during the WCW vs. WWF rivalry in the late 90's, when shows were often changed on the fly in response to something the competing federation was up to.
The position late 2013/early 2014 Daniel Bryan has been in smacks of this. After setting up a seemingly interesting storyline between a now-heelTriple H (playing the Corrupt Corporate Executive) and a chosen championRandy Orton, Bryan got shoved into the background of his own feud after the Hell in a Cell pay-per-view and basically sat on the sidelines (feuding with The Wyatt Family) during the run-up to the TLC event (where Orton and John Cena were scheduled to unify the WWE and World Heavyweight championships). Fan reaction towards this was overwhelmingly negative and only got louder when Batista returned and won the Royal Rumble (at a time when everyone expected Bryan to pull it off). Eventually this fan reaction hit home in the creative department and Bryan's very short two week face-heel-face turn in Januarynote Apparently caused by sports fans using the "YES!" chants at games and the leadup to WrestleMania XXX is showing a drastic change in plans from the original blueprints. It's likely had things gone as were planned, the main event of Batista vs. Orton at WrestleMania would have been the end result.
This is how Douglas Adams wrote the original radio scripts for The Hitchhiker's Guide to the Galaxy. Apparently, he'd often still be rewriting the ends of episodes as the cast were recording the beginning. According to a making-of feature, the actor who was supposed to play the Ruler of the Universe (who appears in the final minutes of the last episode of season two) actually went home because it took Adams so long to finish the script. The role was cast by handing the pages to the one actor still in the studio who didn't have another part in that scene. In fact, the second series' deadlines for the scripts were so tight that his producers essentially locked him in a hotel room to force him to hit them.
Extremely major characters were accidentally created this way - Zaphod Beeblebrox first appears in Fit The First as the person to whom a quote about Pan-Galactic Gargle Blasters is attributed in one of the story's many Cutaway Gags, with the hint 'we will learn more of his wisdom later'. After having both Ford and Arthur chucked out of an airlock into space with no spacesuits as a cliffhanger just because he thought it would be funny, and being unable to come up with a solution for saving them that wasn't a total Deus ex Machina, he decided to exploit the improbability of their being saved by coming up with a spaceship powered entirely by improbability, creating the Infinite Improbability Drive. In order to find a pilot for the ship, he quickly grabbed the name Zaphod Beeblebrox to make it look like Foreshadowing, fleshed out his position in an interesting way, and added in the character of Trillian to act as a Doctor Who-like companion figure for him.
The Tsar Bomba was designed while it was being built, due to having mere weeks to build the biggest nuke ever detonated.
Penny Arcade is written without a Strip Buffer, so the creators can stay up-to-date on gaming news. Different reason for the trope, same idea. It helps that it's a gag-a-day strip, rather than needing any sort of continuity.
MS Paint Adventures, especially in the earlier adventures. The latest adventure, Homestuck, is the only one to have any sort of planning before being written, having started with the four central characters, their weapons of choice, some generalgamemechanics, and a handful of plot points, including an ending, worked out beforehand. The rest of the universe-spanning, time-traveling, chronology-fucking, nearly 4000 pages of extremely convoluted plot has been made along the way.
Questionable Content gets points for being a Monday through Friday comic that is not only drawn without a Strip Buffer, but is written and drawn by Jeph Jacques literally the night before. Sometimes if he's struck by a burst of inspiration, he'll do two comics in a day, waiting to post the second one, and sometimes if he's stuck for an idea he won't start drawing until 3 AM...
Ursula Vernon has gone on record as saying she expected Digger to be over in the first twelve pages or so. Needless to say, it wasn't— it took four years and almost eight hundred pages for Digger's story to be fully told, and that's not counting the side stories that went in the printed editions.
Repeatedly on the forum for The Whiteboard, Doc Nickel has admitted that he makes up the strips as they go, without any previous planning. This has occasionally resulted in an Aborted Arc like one year's Thanksgiving storyline.
The BIONICLE serials are apparently written like this, although the main plot is carefully planned out years in advance. The serials tend to cover the lesser-known characters and don't affect the main story much, so they are able to have this sort of freedom.
Now, as there is no main plot to be told, the serials took over. This means the entire story has become an example.
Darwin's Soldiers: Serris states that nearly everything he write was improvised on the fly, including the two sequels.
Mr. Mendo's Hack Attack, nowadays, is completely improvised and more or less created entirely through the editing process. Ironically, this has led to new episodes coming out more frequently.
wildbow, author of Worm, makes a point of this as one way of making the writing process more interesting for himself. Virtually every chapter of Worm is written just the day before publishing, often finishing shortly before the midnight deadline, and he has set himself a minimum-length of 6000 words. He has missed an update only twice-both by mere minutes, and both times due to technical issues.
Despite this, much of the plot itself was planned out prior to writing; Interlude 26 had been planned for since the very beginning, according to Word of God.
Ursula Vernon, the author of Digger, commented several times that she knew the general outline of the story but not the details, and a number of plot elements she introduced early on that later became important Chekhov's Guns were never really intended to be at the time; the weird little details that never turned into anything look like they're just world-building, while the ones that did become important later make it look like she had a huge intricate plan all along.
The storyline "manga" on Gaia Online tells an unbelievably convoluted story. It's so twisty and swerve-y, in fact, that the writers and artists responsible for pushing out storyline updates have joked that even they stopped paying attention to what happens at some point or other.
Most episodes of South Park are pitched, storyboarded, written, animated, voice-recorded, and put on the air in the stretch of about one single week, one episode at a time. To contrast, most animated series take nine months per episode, with several episodes being in various stages of production at any given moment. This is why South Park's topical humor is more current than, say, what The Simpsons does. The only time this trope backfired on them was when "Goth Kids 3: Dawn of the Posers" from season 17 had to be postponed due to a power outage.
The writers of Beast Wars admitted in DVD Bonus Content that they were winging it as they were going along. They also said that things went Up to Eleven around the time of the season finales as they weren't always sure they would get renewed for another season so they just adopted a "kill them all, let Hasbro sort it out" view when writing these episodes. This led to one particularly infamous moment where Inferno is utterly vaporized in a scene clearly intended to be a death scene. In the next season he turns up burnt but otherwise unharmed.
If Word of God is anything to go by, Adventure Time is half carefully plotted out and half completely made up on the fly. This leads to such things as Princess Bubblegum turning 13 then being turned back to normal in the next episode because the writers weren't sure what to do with a plot point like that or Lemongrab becoming a full-blown cast member despite being intended to never appear again after his introductory episode.