Undertale

• 1. Introduction

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  Undertale began as a request for US$5,000. When the crowdfunding campaign for the role-playing game closed on the 25th of July 2013, 2,398 backers had pledged US$51,124, more than ten times the goal. Behind the page stood Toby Fox, an American indie developer with little experience making games. The premise sounds simple. A child falls into a hidden region under the Earth and must find a way home past a crowd of monsters. Yet the game lets the player decide, again and again, whether any of those monsters has to die. How did one person build nearly everything in a game of this scale? What does it mean to win a battle by refusing to finish it? And why did a game about mercy gather a fandom that argued fiercely over how it should be played?

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• 2. Built By One Person

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  In December 2012, Toby Fox was casually reading an online reference article about array data structures, a subject he knew nothing about. The page set him thinking about how arrays could drive a text system for a role-playing game. Once that system worked, he began imagining a battle system. He built both in GameMaker: Studio, and the two grew so intertwined that the battle system shaped how he wrote the story.

  Fox had been tinkering with games for years before that. He and his three brothers often made role-playing games in RPG Maker 2000, though few of those projects were ever finished. In high school he also worked on several EarthBound ROM hacks. Undertale was the first full game he wrote.

  His aim was a role-playing game that broke from traditional design. Fox loved Japanese role-playing games but often found them "boring to play". He wanted memorable characters, and he wanted the medium itself to tell the story, rather than keeping story and gameplay in separate boxes.

  The work stretched across 32 months. The original plan was a game of about two hours, due in mid-2014, but delays pushed it far past that mark. A first demo appeared on the 23rd of May 2013, and at the time it represented about 25 percent of the finished game.

  Apart from the art, Fox did everything himself, including the script and the music, partly so he would not have to rely on others. Temmie Chang served as main artist, supplying most of the sprites and concept art, while other guest designers contributed character designs. Fox said a bigger art team would probably not have changed the look. He pointed to a psychological idea that audiences grow more attached to characters drawn simply than to ones drawn in detail.

  The title came from wordplay. Fox noticed that EarthBound and Homestuck were each two words stuck together, and he wanted a name that was similarly catchy. He also borrowed from Cave Story, swapping "story" for "tale" and "Cave" for "Under", since his game took place underground.

  Looking back, Fox called the finished game "a huge katamari of things that he likes that he combined arbitrarily". He admitted that part of the story was written almost improvisationally at the last minute.

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• 3. Mercy Mechanics

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  During a fight in Undertale, the player controls only a small heart that stands for the soul. The heart must dodge attacks from the opposing monster, much as in a bullet hell shooter. Later battles add colored obstacles and bosses that change how the heart moves. Attacking requires timed button presses, and killing earns EXP, which raises a stat called LOVE, along with gold.

  The ACT option is where the game turns unusual. It lets the player check an enemy's attack and defense, and it offers other actions that differ from monster to monster. Respond correctly, or wear a monster down to low HP without killing it, and the player can choose to spare it and end the fight. Some bosses can be finished peacefully only if the player survives until the character has stopped speaking. Monsters talk throughout a battle, and the game describes their feelings and actions. Their attacks shift depending on how the player treats them.

  Because of these choices, the game has several story branches and endings, and it is possible to finish without killing a single enemy. On a second playthrough, boss dialogue changes to reflect what the player did before. This is one of several metafictional touches in both the gameplay and the story.

  Fox wanted the defensive half of combat to be as engaging as Super Mario RPG from 1996 and Mario & Luigi: Superstar Saga from 2003. The Mario & Luigi series, along with bullet hell shooters such as the Touhou Project series, inspired the dodging. He built a mechanic he would personally enjoy. He ruled out required grinding and fetch quests, since fetch quests mean backtracking, which he dislikes.

  To test difficulty, Fox asked friends with no bullet hell experience to play, and they were able to finish. He judged the balance right, especially given the complications of adding a second difficulty setting.

  The talking side came from Shin Megami Tensei, a series from 1992 in which players can talk to monsters to avoid fighting. Fox wanted to expand that idea, since failed negotiation there simply forces a battle. In his words, "I want to create a system that satisfied my urge for talking to monsters". As he built it, the idea of finishing without killing anyone "just evolved naturally". He never considered removing the option to fight. Asked how hard a no-kill run is, he called it "the crux of one of the major themes of this game" and urged players to think it through themselves.

  One more influence came from Moon: Remix RPG Adventure, released in 1997. In that game the player repairs the damage done by the "Hero" and raises a "Love Level" by helping people. Fox took inspiration from those concepts even though he had never played it.

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• 4. Three Endings

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  Mount Ebott holds the only gap in the magic barrier that seals the Underground from the surface. Monsters were banished below after a war with humans, and a human child falls through that gap as the game opens. Waiting there is Flowey, a sentient flower who teaches the game's mechanics and then lies about "LV", or "LOVE", in an attempt to kill the child. Toriel, a motherly goat-like monster, rescues the child and teaches how to survive without killing. She hopes to adopt the child and shield them from Asgore, the king.

  The child eventually leaves Toriel and heads for Asgore's castle, where the barrier lies. Along the way are the skeleton brothers Sans and Papyrus, sentries for the Snowdin forest. There are also Undyne, head of the royal guard, Alphys, the royal scientist, and Mettaton, a robotic television host that Alphys created. Most of these monsters can be fought, killed, or spared and possibly befriended.

  The reason for Asgore's war lies with his son Asriel. Many years earlier, Asriel, son of Asgore and Toriel, befriended the first human to fall into the Underground. When that child suddenly died, Asriel used the child's soul to pass through the barrier, hoping to carry the body home. Humans on the surface attacked and killed him, and Asgore declared war. By the present day, Asgore has gathered six human souls and needs just one more to shatter the barrier.

  The "Neutral" ending arrives if the player killed some monsters, or none, but did not complete the pacifist route. Before the fight with Asgore, Sans stops the child and explains that "LOVE" and "EXP" stand for "level of violence" and "execution points". He then judges the child by those totals. Flowey interrupts the Asgore fight, kills the king, and steals the human souls to become a larger, grotesque form. With help from the souls, the child defeats Flowey and may kill or spare him. A phone call from Sans later describes how the Underground fares after the child's departure.

  A player who kills nobody can reload a saved game and reach the "true pacifist" ending. Here Flowey is revealed as a reincarnation of Asriel, created through Alphys's experiments. Just before the Asgore fight, Toriel halts the battle, joined by every monster the child befriended. Flowey ambushes them and absorbs all the souls, human and monster, to take an older Asriel's form. The child reaches the souls of their friends and defeats him. Asriel returns to his child form, destroys the barrier, voices remorse, and reveals the child's true name as Frisk. The monsters then rejoin the humans in peace, and the child may accept Toriel as an adoptive mother.

  The third ending, known to fans as "No Mercy" or "Genocide", demands that the player kill every fightable monster. That means triggering random encounters in each area until none remain. Along this route, many characters flee, and those who stay speak with altered dialogue that reflects what the player is doing. Sans tries to stop the child at Asgore's castle and is slain. Flowey kills Asgore, hoping to obtain mercy, but the child kills Flowey. Then Chara, the first fallen child who befriended Asriel, appears and erases the world. To play again, the player must give their soul to Chara, which restores the world and permanently alters the true pacifist ending.

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• 5. Writing the Monsters

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  Toriel was written as a parody of tutorial characters. Fox strongly disliked Fi, the companion in The Legend of Zelda: Skyward Sword, who often reveals puzzle answers early. He also felt that role-playing games rarely offer strong mothers. In the Pokemon series and in Mother, he thought mothers served as "symbols rather than characters". So he aimed for "a mom that hopefully acts like a mom" who "genuinely cares" about what players do.

  In early versions, the player had to kill Toriel to progress. Fox decided that this was wrong and changed it before the demo came out. That decision pushed him to add the option to spare monsters, and it clarified for him what the game was really about.

  Fox wanted every monster to feel like an individual. He held up the Final Fantasy series as the opposite, saying that all monsters in RPGs like it are the same and that there is no meaning to that. The idea of being trapped underground came from the video game Brandish. He also drew on the silliness of internet culture, on comedy shows like Mr. Bean, and on the unsettling mood of EarthBound. He found that writing flowed more easily once a character's voice and mood were set.

  Papyrus and Sans are named after the typefaces Papyrus and Comic Sans, and their dialogue appears in those fonts. The credits list both as inspired by J. N. Wiedle, author of Helvetica, a webcomic about a skeleton named after the font. Papyrus began as a sketch in Fox's notebook, a mean-spirited character called "Times New Roman" who wore a fedora. Sans originally ran poker at a casino and was meant to tell more puns, but Fox realized the jokes would not land as he had hoped. The casino idea returned in the Xbox One port, where Sans runs one at the brothers' house.

  Fox named the date scene, where Papyrus rejects Frisk, as the most memorable part of making the game. It was originally harsher. A playtester, a friend of Fox and a fan of Papyrus, cried during the scene, and Fox softened it.

  Undyne proved hard to write. Fox tried her with various accents and hobbies, and the one detail that held was that she is the first boss who actively wants to kill the protagonist. Alphys was first drawn as a man, but Fox grew to dislike that, so she became a woman and gained eyelashes. Asgore was meant to be intimidating but became goofier, inspired by Fox's friend Reid Young, founder of Fangamer, the company that would later publish the retail console edition.

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• 6. Soundtrack of a Solo Act

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  FL Studio was the only tool Toby Fox needed for the entire Undertale score. A self-taught musician, he wrote most tracks with little revision. Only the main theme, "Undertale", went through multiple iterations. He had been composing for the webcomic Homestuck since 2010, and that work, along with the music of Super NES role-playing games like EarthBound and the Touhou Project series, shaped the sound.

  Over 90 percent of the songs were written specifically for the game. The exception is "Megalovania", the theme of the boss battle with Sans, which had already appeared in Homestuck and in one of Fox's EarthBound ROM hacks. For each section of the game, he composed the music before programming, because it helped him decide how the scene should go. He first tried the music tracker FamiTracker but found trackers unintuitive, so he played segments separately and joined them on a track.

  Critics treated the score as a key reason for the game's success, especially its character leitmotifs that recur across many tracks. USgamer's Nadia Oxford singled out "Hopes and Dreams", the boss theme for the Asriel fight on the Pacifist route. It weaves in most of the main characters' themes and, in her words, is "a perfect way to cap off your journey". She said it shows Fox's skill at turning old songs into new experiences. GameSpot's Tyler Hicks compared the music to "bit-based melodies".

  The soundtrack went on to a long afterlife. Materia Collective released the official soundtrack on the same day as the game. Cover albums followed, including the 2015 metal and electronic album Determination by RichaadEB and Amie Waters, and the 2016 jazz album Live at Grillby's by Carlos Eiene. To mark the first anniversary in 2016, Fox posted five unused musical works on his blog. Four of the game's songs became official downloadable additions for Taito's Groove Coaster on Steam.

  For the fifth anniversary, Fox streamed footage, with permission, of a 2019 concert of the songs by the Japanese orchestra group Music Engine. On the 17th of March 2026, a concert tour of the soundtrack for a 25-piece orchestra, curated by Fox, was announced. Performances were scheduled to begin on the 23rd of August 2026 and continue through 2027 across North America, Europe, the United Kingdom, Asia and Australia.

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• 7. Beyond the PC

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  On the 15th of September 2015, Undertale reached players on OS X and Windows. A Linux version followed on the 17th of July 2016. Fox wanted more platforms, but Nintendo 3DS and Wii U ports were not possible because GameMaker did not support those machines. A patch in January 2016 fixed bugs and added new lines of dialogue and secrets.

  At E3 2017, Sony announced a PlayStation 4 and PlayStation Vita release, with a retail edition published by Fangamer. Those versions arrived in August 2017 with new achievements and a new location, the Dog Shrine. A Nintendo Switch version was revealed during a March 2018 Nintendo Direct. Its release highlighted a deal between Nintendo and YoYo Games that lets GameMaker Studio 2 users export directly to the Switch. The Switch edition reached Japan on the 15th of September 2018 and the wider world on the 18th, with an exclusive boss fight against Mad Mew Mew. The Xbox One version came on the 16th of March 2021 and put a playable slot machine in the Dog Shrine.

  Japan took a path of its own. After the game's release, a small Japanese fan community emerged and put out an unofficial translation patch in early 2016. Fox had always pictured a Japanese version as an eventual goal, so he consulted several companies and chose 8-4, which had previously translated Aquaria and Shovel Knight. All the console ports were developed and published by 8-4 in every region.

  To keep a consistent voice, 8-4 assigned just one primary translator, Keiko Fuchicho, even though that slowed the release. She was supported by a small team of editors and proofreaders, plus a programmer who adapted the game to Japanese writing systems. Before work began in early 2016, Fox handed over development notes and annotated dialogue, and he kept advising the team. Because PC gaming is less prominent in Japan, they decided to release for consoles at the same time.

  The Japanese pronoun chosen for Sans surprised many fans, because it carries a connotation of rural life. The reaction earned its own name, "oira shock". The Japanese PC version followed on the 22nd of August 2017, days after the console release.

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• 8. Acclaim and Aftershocks

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  On Metacritic, Undertale earned "universal acclaim", ranking as the third-highest rated Windows game of 2015 and among the top 50 of all time. For a time after release it was the highest-rated PC game ever on that site. OpenCritic showed 97 percent of critics recommending it. GameSpot's Tyler Hicks called it "one of the most progressive and innovative RPGs to come in a long time", and IGN's Kallie Plagge called it "a masterfully crafted experience". Plagge also praised the option to avoid combat through friendly conversation.

  Reviewers admired the writing. The Escapist's Ben Croshaw named it the best-written game of 2015, saying it is hilarious on one hand and rather heartfelt by the end. Game Informer's Daniel Tack called the combat "incredibly nuanced". The visuals divided opinion. Plagge said the game "isn't always pretty" but felt the music and animation made up for it. Croshaw said the art "wobbles between basic and functional to just plain bad", while PC Gamer's Richard Cobbett praised how well it conveys emotion.

  Scholars read the game as a comment on violence. Essayist Sean Travers, writing in the Journal of Popular Culture, described Undertale as a critique of mainstream role-playing games where players kill enemies for experience points. She noted that the Genocide route punishes players who ignore its warnings through a darkening tone and disturbing imagery. In her reading, the player becomes a "postmodern psychopath".

  Sales climbed quickly. A preliminary Steam Spy report counted 530,343 copies sold on Steam by the end of 2015. By early February 2016, the game had passed one million sales, and by July 2018 an estimated three and a half million people were playing on Steam. In Japan, digital sales on PlayStation 4 and PlayStation Vita passed 100,000 copies by February 2018. Steam Spy now estimates between 5 and 10 million copies sold on Steam.

  Honors piled up as well. IGN gave it Best Story in its Best of 2015, and in 2016 it won the Audience Award at the Independent Games Festival. The SXSW Gaming Awards named it the Most Fulfilling Crowdfunded Game. IGN ranked it 20th on its 2021 list of the top 100 games of all time, and a nationwide TV Asahi poll of over 50,000 players in Japan put it 13th.

  Fox found the attention stressful. About a year after release, he said it would not surprise him if he never made a game as successful again, and that this was fine with him. Reid Young, CEO of Fangamer, called the game "an absolutely dominating force". Sans became a favorite subject of fan works. Wrestler Kenny Omega dressed as Sans for the 30th of October 2019 episode of All Elite Wrestling: Dynamite. In September 2019, Nintendo released a Sans Mii Fighter costume for Super Smash Bros. Ultimate with a new arrangement of "Megalovania", after director Masahiro Sakurai noted how often players asked for him. The fan game Undertale Yellow, after seven years of development, arrived in 2023 to enthusiastic reception.

  The fandom also earned a reputation for conflict. Fans disagreed over the correct way to play, and some live streamers were harassed for killing enemies or attempting the genocide route. YouTuber Markiplier refused to finish his first playthrough, saying he was "not having fun" because of fan demands.

  Mercy found its way to the Vatican, too. In July 2016, during an internet summit there, YouTube personality MatPat gave Pope Francis a copy of the game, linking the gift to the Extraordinary Jubilee of Mercy. In January 2022, a circus troupe performed for the Pope at his weekly audience to the tune of "Megalovania".

  Fox's next project arrived on the 31st of October 2018, when he released the first chapter of Deltarune for free. Fox said it is "not the world of Undertale", though some characters and settings may recall it, and that it is meant for people who have finished Undertale. The name is an anagram of Undertale. Unlike its predecessor, Deltarune is marketed as having a single ending no matter what the player chooses. Chapter 2 came out free on the 17th of September 2021, once Fox had assembled a team to help. Chapters 1 through 4 were released as a paid package on the 4th of June 2025, and all future chapters will arrive as free updates.

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