Undertale is a role-playing video game created by American indie developer Toby Fox. The player controls a child who has fallen into the Underground: a large, secluded region under the surface of the Earth, separated by a Magic barrier. The player meets various monsters during the journey back to the surface. Some monsters might engage the player in a fight. The combat system involves the player navigating through mini-bullet hell attacks by the opponent. They can opt to pacify or subdue monsters in order to spare them instead of killing them. These choices affect the game, with the dialogue, characters, and story changing based on outcomes.

Fox developed the entirety of the game independently, including writing and composing the score.

Additional art was created by other artists, primarily Temmie Chang.

The game took inspiration from several sources.

These include the Mother and Mario & Luigi role-playing series, the bullet hell shooter series Touhou Project, and the British comedy show Mr. Bean. Originally, Undertale was meant to be two hours in length and was set to be released in mid-2014. However, development was delayed over the next three years.

The game was released for Microsoft Windows and OS X in September 2015. It was also ported to Linux in July 2016, PlayStation 4 and PlayStation Vita in August 2017 and the Nintendo Switch in September 2018. The game was acclaimed for its thematic material, intuitive combat system, musical score, originality, story, dialogue, and characters. The game sold over one million copies and was nominated for multiple accolades and awards. Several gaming publications and conventions listed Undertale as Game of the Year. The first chapter of a related game, Deltarune

Undertale is a role-playing game that uses a top-down perspective.^[3] In the game, players control a child and complete objectives in order to progress through the story.^[4] Players explore an underground world filled with towns and caves, and are required to solve numerous puzzles on their journey.^[4][5] The underground world is the home of monsters, many of whom challenge the player in combat;^[5] players decide whether to kill, flee, or befriend them.^[4][6] Choices made by the player radically affect the plot and general progression of the game, with the player's morality acting as the cornerstone for the game's development.

When players encounter enemies in either scripted events or random encounters, they enter a battle mode. During battles, players control a small heart which represents their soul, and must avoid attacks unleashed by the opposing monster similar to a bullet hell shooter.^[4][5] As the game progresses, new elements are introduced, such as colored obstacles, and boss battles which change the way players control the heart.^[7] Players may choose to attack the enemy, which involves timed button presses. Killing enemies will cause the player to earn EXP (in turn increasing their LOVE) and gold.^[8] They can use the ACT option to perform various actions, which vary depending on the enemy.^[4] If the player uses the right actions to respond to the enemy, or attacks them until they have low HP (but still alive) they can choose to spare them and end the fight without killing them.^[9] For some boss encounters to be completed peacefully, the player is required to survive until the character they are facing has finished their dialogue. The game features multiple story branches and endings depending on whether players choose to kill or spare their enemies; and as such, it is possible to clear the game without killing a single enemy.^[10]

Monsters will talk to the player during the battle, and the game will tell the players what the monster's feelings and actions are.^[11] Enemy attacks change based on how players interact with them: should players choose non-violent options, enemy attacks are easy, whereas they become difficult if players choose violent options.^[5][11] The game relies on a number of metafictional elements in both its gameplay and story.^[12] When players participate in a boss battle on a second playthrough, the dialogue will be altered depending on actions in previous playthroughs.^[13]

Undertale takes place in the Underground, a realm where monsters, once equal to humans, were banished to after war broke out between them. The Underground is sealed from the surface world by an imperfect magic barrier, the only point of entry being at Mount Ebott.^[14] A human child falls into the Underground and encounters Flowey, a sentient flower who teaches them the game's mechanics and encourages them to raise their "LV", or "LOVE", by gaining "EXP" through killing monsters.^[1] When Flowey attempts to murder the human to take their soul for himself, the human is rescued by Toriel, a motherly goat-like monster, who teaches the human to solve puzzles and survive conflict in the Underground without killing. She intends to adopt the human, wanting to protect them from Asgore Dreemurr, the king of the Underground.

The human eventually leaves Toriel to search for Asgore's castle, which contains the barrier leading to the surface world.

Along the way, the human encounters several monsters, including: the skeletons Sans and Papyrus, two brothers who act as sentries for the Underground; Undyne, the head of the royal guard; Alphys, the kingdom's royal scientist; and Mettaton, a robotic television host Alphys created. Some of them are fought, with the human having to choose whether to kill them or to show mercy; should the human spare them, they may choose to become friends. During their travels, the human learns the cause of the war between humans and monsters. Asriel, the son of Asgore and Toriel, befriended a human child who fell into the Underground and was adopted by Asgore and Toriel. One day, the child was fatally poisoned by some flowers. When Asriel returned their body to the humans, they attacked and killed him, resulting in Asgore declaring war. Asgore now seeks to break the barrier, which requires him to collect seven human souls, of which he has six.

The game's ending depends on how the player resolved encounters with monsters.^[10][2] If the player killed some but not all monsters, the human arrives at Asgore's castle and learns that they also need a monster's soul to cross the barrier, forcing them to fight Asgore. Sans stops the human before their confrontation, revealing that the human's "LOVE" is an acronym for "level of violence" and "EXP" for "execution points." Sans judges the human based on the combined resolution of the encounters. The human fights Asgore, but Flowey interrupts them, killing Asgore and stealing the human souls. With the aid of the rebelling souls, the human defeats Flowey, falls unconscious, and awakens on the human side of the barrier; they receive a phone call from Sans, explaining the state of the Underground after the human's departure.

If the player instead kills no monsters and has completed a previous playthrough of the game,^[13] Flowey is revealed to be a reincarnation of Asriel, created as part of Alphys's experiments.

Toriel intervenes before the human fights Asgore and is joined by the other monsters the human has befriended.

Flowey ambushes the group, using the souls of all the monsters to take an older Asriel's form to fight the human.

The human connects with their new friends during the fight, eventually triumphing.

Asriel reverts to his child form, destroys the barrier, and expresses his remorse to the others before leaving.

The human falls unconscious and is awoken to see their friends surrounding them, with the knowledge of the human's name – Frisk.

The monsters reintegrate with the humans on the surface, while Frisk has the option of accepting Toriel as their adoptive mother.

Another ending ensues if the player kills all monsters,^[13][13] in which Frisk becomes influenced by Chara, the fallen human child whose body Asriel attempted to return. When Frisk reaches Asgore's castle, Sans attempts to stop them, but Frisk kills him. Flowey kills Asgore in an attempt to get mercy, but Frisk executes Flowey anyway. The fallen human child assumes control and, with or without the player's consent, destroys the universe. To enable further replays of the game, Frisk must first give their soul to the fallen human child in exchange for restoring the universe, which will permanently alter every subsequent Pacifist run.

Undertale was developed by Toby Fox across 32 months.^[18] Development was financed through a crowdfunding campaign on the website Kickstarter. The campaign was launched on June 25, 2013 with a goal of US$5,000; it ended on July 25, 2013, with US$51,124 raised by 2,398 people (1022.48% of the original goal).^[19] Undertale's creation ensued after Fox created a battle system using the game creation system GameMaker: Studio.^[20] He wanted to develop a role-playing game that was different from the traditional design, which he often found "boring to play".^[21] He set out to develop a game with "interesting characters", and that "utilizes the medium as a storytelling device... instead of having the story and gameplay abstractions be completely separate".^[21]

Fox worked on the entire game independently, besides some of the art; he decided to work independently to avoid relying on others.^[18] Fox had little experience with game development; he and his three brothers often used RPG Maker 2000 to make role-playing games, though few were ever completed. Fox also worked on several EarthBound ROM hacks while in high school.^[21] Temmie Chang worked as the main artistic assistant for the game, providing most of the sprites and concept art.^[22][23] Fox has said that the game's art style would likely remain the same if he had access to a larger team of artists. He found that "there's a psychological thread that says audiences become more attached to characters drawn simply rather than in detail", particularly benefiting from the use of visual gags within the art.^[24]

The defensive segment within the battle system was inspired by the Mario & Luigi seriesTouhou Project seriesseries]] ^[25][26]Super Mario RPG Mario & Luigi: Superstar Saga grinding fetch quests^[18] In terms of the game's difficulty, Fox ensured that it was easy and enjoyable. He asked some friends who are inexperienced with bullet hell shooters to test the game, and found that they were able to complete it. He felt that the game's difficulty is optimal, particularly considering the complications involved in adding another difficulty setting.^[27]

The game's dialogue system was inspired by Shin Megami Tensei (1992),^[25] particularly the gameplay mechanic whereby players can talk to monsters to avoid conflict. Fox intended to expand upon this mechanic, as failing to negotiate resulted in a requirement to fight. "I want to create a system that satisfied my urge for talking to monsters," he said.^[5] When he began developing this mechanic, the concept of completing the game without killing any enemies "just evolved naturally".^[28] However, he never considered removing the option to fight throughout development.^[28] When questioned on the difficulty of playing the game without killing, Fox responded that it is "the crux of one of the major themes of this game", asking players to think about it themselves.^[28] Certain parts of the game, such as the "CORE" area, as well as the plot pace and progression of the game and minor references, draw strong parallels with Chrono Trigger

For the game's writing, Fox was partly influenced by the silliness of internet culture, as well as comedy shows like Mr. Bean.^[18] He was also inspired by the unsettling atmosphere of EarthBound.^[18] Fox's desire to "subvert concepts that go unquestioned in many games" further influenced Undertale's development.^[28] Fox found that the writing became easier after establishing a character's voice and mood. He also felt that creating the world was a natural process, as it expressed the stories of those within it.^[24] Fox felt the importance to make the game's monsters "feel like an individual".^[25] He cited the Final Fantasy seriesseries]]posite; "all monsters in RPGs likeasy are the same... there's no meaning to that".^[25]

The character of Toriel, who is one of the first to appear in the game, was created as a parody of tutorial characters.

Fox strongly disliked the use of the companion character Fi in The Legend of Zelda: Skyward Sword, in which the answers to puzzles were often revealed early. Fox also felt that role-playing video games generally lack mother characters; in the Pokémon seriesseries]] as* Mother EarthBoundx felt that the mothers are used as "symbols rather than characters".^[21] In response, Fox intended for Toriel's character to be "a mom that hopefully acts like a mom", and "genuinely cares" about players' actions.^[21]

The game's soundtrack was entirely composed by Fox.

A self-taught musician, he composed most of the tracks with little iteration; the game's main theme, "Undertale", was the only song to undergo multiple iterations in development.

The soundtrack was inspired by music from Super NES role-playing games,^[18] such as EarthBound,^[31] as well as the webcomic Homestuck, for which Fox provided some of the music.^[18] Fox also stated that he tries to be inspired by all music he listens to,^[26] particularly those in video games.^[31] According to Fox, over 90% of the songs were composed specifically for the game.^[20] "Megalovania", the song used during the boss battle with Sans, had previously been used within Homestuck and in one of Fox's EarthBound ROM hacks.^[30][32] For each section of the game, Fox composed the music prior to programming, as it helped "decide how the scene should go".^[20] He initially tried using a music tracker to compose the soundtrack, but found it difficult to use. He ultimately decided to play segments of the music separately, and connect them on a track.^[31] To celebrate the one year anniversary of the game, Fox released five unused musical works on his blog in 2016.^[33] Four of the game's songs were released as official downloadable content for the Steam version of Taito's Groove Coaster.^[32]

Undertale's soundtrack has been well received by critics as part of the success of the game, in particular for its use of various leitmotifs for the various characters used throughout various tracks.^[34][35] In particular, "Hopes and Dreams", the boss theme when fighting Asriel in the run-through where the player avoids killing any monster, brings back most of the main character themes, and is "a perfect way to cap off your journey", according to USgamer's Nadia Oxford.^[30] Oxford notes this track in particular demonstrates Fox's ability at "turning old songs into completely new experiences", used throughout the game's soundtrack.^[30] Tyler Hicks of GameSpot compared the music to "bit-based melodies".^[36]

The game was released on September 15, 2015 for Microsoft Windows and OS X,^[37] and on July 17, 2016 for Linux.^[38] Fox expressed interest in releasing Undertale on other platforms, but was initially unable to port it to Nintendo platforms without reprogramming the game due to the engine's lack of support for these platforms.^[18] A patch was released in January 2016, fixing bugs and altering the appearance of blue attacks to help colorblind players see them better.^[39] Sony Interactive Entertainment announced during E3 2017 that Undertale would get a release for the PlayStation 4 and PlayStation Vita, a Japanese localization, and a retail version published by Fangamer. These versions were released on August 15, 2017.^[40][41][42] A Nintendo Switch version was revealed during a March 2018 Nintendo Direct, though no release date was given at the time;^[43][44] Undertale's release on Switch highlighted a deal made between Nintendo and YoYo Games to allow users of GameMaker Studio 2 to directly export their games to the Switch.^[45] The Switch version was released on September 15, 2018 in Japan,^[46] and on September 18, 2018 worldwide.^[47] All console ports are published courtesy of Japanese localizer 8-4 in all regions.

Other Undertale media and merchandise have been released, including toy figurines and plush toys based on characters from the game.^[48] The game's official soundtrack was released by video game music label Materia Collective in 2015, simultaneously with the game's release.^[49] Additionally, two official Undertale cover albums have been released: the 2015 metal/electronic album Determination by RichaadEB and Ace Waters,^[50][51] and the 2016 jazz album Live at Grillby's by Carlos Eiene, better known as insaneintherainmusic.^[52] Another album of jazz duets based on Undertale's songs, Prescription for Sleep, was performed and released in 2016 by saxophonist Norihiko Hibino and pianist Ayaki Sato.^[53] A 2xLP vinyl edition of the Undertale soundtrack, produced by iam8bit, was also released in the same year.^[54] Two official UNDERTALE Piano Collections sheet music books and digital albums, arranged by David Peacock and performed by Augustine Mayuga Gonzales, were released in 2017 and 2018^[55][56] by Materia Collective. A Mii Fighter costume based on Sans was made available for download in the crossover title Super Smash Bros. Ultimate in September 2019. This costume also adds a new arrangement of "Megalovania" by Fox as a music track.^[57]

After previously teasing something Undertale-related a day earlier, Fox released the first chapter of Deltarune on October 31, 2018 for Windows and macOS for free.^[58] Deltarune is "not the world of Undertale", according to Fox, though characters and settings may bring some of Undertale's world to mind,^[59] and is "intended for people who have completed Undertale";^[60] the name Deltarune is an anagram of Undertale.^[61] Fox stated that this release is the first part of a new project, and considered the release a "survey program" to determine how to take the project further.^[61] Fox clarified that Deltarune will be a larger project than Undertale; Fox stated it took him a few years to create the first chapter of Deltarune, much longer than it took him to complete the Undertale demo. Because of the larger scope, he anticipates getting a team to help develop Deltarune, and has no anticipated timetable when it will be completed. Once the game is ready, Fox will release the game as one whole package.^[59] Fox plans for Deltarune to have only one ending, regardless of what choices the player makes in the game.^[59]

Undertale received critical acclaim, and was quickly considered a cult video game by numerous publications.^[70][71] Review aggregator Metacritic calculated an average score of 92 out of 100, based on 43 reviews.^[62] Metacritic ranks the game the third-highest rated Windows game released in 2015,^[62] and among the top 50 of all time.^[72] Praise was particularly directed at the game's writing, unique characters, and combat system. GameSpot's Tyler Hicks declared it "one of the most progressive and innovative RPGs to come in a long time",^[36] and IGN's Kallie Plagge called it "a masterfully crafted experience".^[13] By the end of 2015, in a preliminary report by Steam Spy, Undertale was one of the best-selling games on Steam, with 530,343 copies sold.^[73] By early February 2016, the game surpassed one million sales,^[74] and by July 2018, the game had an estimated total of three and a half million players on Steam.^[75] Japanese digital PlayStation 4 and PlayStation Vita sales surpassed 100,000 copies sold by February 2018.^[76]

Daniel Tack of Game Informer called the game's combat system "incredibly nuanced", commenting on the uniqueness of each enemy encounter.^[67] Giant Bomb's Austin Walker praised the complexity of the combat, commenting that it is "unconventional, clever, and occasionally really difficult".^[66] Ben "Yahtzee" Croshaw of The Escapist commended the game's ability to blend "turn-based and live combat elements in a way that actually fucking works".^[77] IGN's Plagge praised the ability to avoid combat, opting for friendly conversations instead.^[13] Jesse Singal of The Boston Globe found the game's ability to make the player empathize with the monsters during combat if they opted for non-violent actions was "indicative of the broader, fundamental sweetness at the core" of Undertale.^[78]

Reviewers praised the game's writing and narrative, with IGN's Plagge calling it "excellent".^[13] The Escapist's Croshaw considered Undertale the best-written game of 2015, writing that is "on the one hand hilarious... and is also, by the end, rather heartfelt".^[77] Destructoid's Ben Davis praised the game's characters and use of comedy, and compared its tone, characters and storytelling to Cave Story (2004).^[4] PC Gamer's Richard Cobbett provided similar comments, writing that "even its weaker moments... just about work".^[68]

The game's visuals received mixed reactions.

Giant Bomb's Walker called it "simple, but communicative".^[66] IGN's Plagge wrote that the game "isn't always pretty" and "often ugly", but felt that the music and animations compensate.^[13] The Escapist's Croshaw remarked that "it wobbles between basic and functional to just plain bad".^[77] Other reviewers liked the graphics: Daniel Tack of Game Informer felt that the visuals appropriately match the characters and settings,^[67] while Richard Cobbett of PC Gamer commended the ability of the visuals to convey emotion.^[68]

About a year after release, Fox commented that he was surprised by how popular the game had become and though appreciative of the attention, he became stressed out over it.

Fox said: "It wouldn't surprise me if I never made a game as successful again.

That's fine with me though."^[79]

Undertale has received multiple awards and nominations from several gaming publications. It won Game of the Year from The Jimquisition^[80] and Zero Punctuation,^[81] as well as Game of the Month from Rock, Paper, Shotgun.^[82] The game won the Best Game Ever poll from GameFAQs,^[83] and was awarded Best PC Game from Destructoid^[84] and IGN.^[85] At the Independent Games Festival Awards, it won the Audience Award,^[86] while the SXSW Gaming Awards named it the Most Fulfilling Crowdfunded Game, and awarded it the Matthew Crump Cultural Innovation Award.^[87]