|Platform(s)||Microsoft Windows, macOS|
Deltarune is a role-playing video game created by American indie developer Toby Fox. The player controls a human, Kris, in a world where monsters live on the surface of the Earth. Kris and a classmate named Susie fall from Earth into a place called the “Dark World” where they meet Ralsei, who informs them that they are heroes destined to restore balance to the world. The players meet various beings who call themselves Darkners during a prophesied quest to seal the dark fountain. Mainly through the combat system, the player navigates through different kinds of bullet hell attacks by enemies, which can be resolved peacefully or through violence. The first chapter of the game was released on October 31, 2018 for Microsoft Windows and macOS. The game's graphics are reminiscent of 16-bit Japanese role-playing games such as EarthBound and Chrono Trigger. 
Deltarune is a spin-off of Fox's previous game, Undertale, but its setting is "not the world of Undertale", according to Fox, though characters and settings may bring some of Undertale's world to mind.
Deltarune, like Undertale, is a role-playing game that uses a top-down perspective. The player controls a human named Kris and has to complete objectives in order to beat the game. During some parts of the game, the player is allowed to choose attacks of other characters in the game. Combat is performed similar to most standard turn-based role-playing games, choosing from a set of actions such as "Attack" or "Spare". While the goal of the game is implicitly to avoid fights and spare monsters, this is made difficult in that Susie, who is not initially controlled by the player, would rather attack enemies than spare them, and thus the player must also determine actions to prevent Susie from hurting enemies if they want to show mercy. The game also has TP (Tension Points), which allow team members to use spells such as "Pacify". The game’s first chapter, unlike Undertale, has only two endings. They are exactly the same up to the king, where, in the pacifist run, all monsters overthrow the king. In neutral, this doesn't happen. Fox plans for the whole game to only have one ending.
This article's plot summary may be too long or excessively detailed. (December 2018) (Learn how and when to remove this template message)
Upon booting up the game, the player is invited to construct an avatar. However, upon completion, the avatar is deleted and the game informs the player that "no one can choose who they are in this world".
The player then assumes control of Kris, a human who lives with their adoptive mother, a monster named Toriel, and Toriel's son Asriel, who is currently away at college. Toriel drops Kris off at school, where Kris and Susie, a delinquent monster classmate, are told to get chalk from the supply closet by their teacher, Alphys. In the closet, they are both pulled into the "Dark World," where their appearances change and they are wearing armor. Soon after, they both meet Ralsei, a prince of the dark, who reveals to them that the three of them are heroes destined to close a geyser of dark energy and restore balance to the world. However, the King has seized control of the Dark World and is determined to prevent this and spread darkness to all worlds.
Susie is initially reluctant to go along with the quest, only being interested in returning to her own world. The group then encounters Lancer, the King's son, who attempts to stop them with various poorly thought out plans. Susie decides to join Lancer's side, leaving Kris and Ralsei to complete the quest on their own. As Kris and Ralsei fight their way to the King's castle, Susie befriends Lancer, and they eventually join forces with Kris and Ralsei. However, Lancer arranges for the group to be thrown into the castle dungeon. Susie escapes and confronts Lancer, who admits that he wanted to keep them from confronting the King, since he doesn't want Susie and his father hurting each other. Susie promises Lancer that she won't hurt the King as the group proceeds to the top of the castle.
The group confronts the King, who refuses to back down and attacks, forcing the group to fight him. Eventually, the group overpowers the King and he apologizes, begging for forgiveness and promising to help them close the dark geyser. Ralsei takes pity on the King and heals him, but it is revealed to be a ruse and the King incapacitates the group with a surprise attack. If Kris has attempted to kill some or all of the monsters they encountered, Susie distracts the King and eventually casts the pacify spell on him, resulting in the King falling asleep. If Kris solved all of their battles nonviolently, then Lancer rallies all of the monsters Kris spared and usurps the King, throwing him in prison and becoming the new ruler of the Dark World.
Regardless of the outcome, the group takes the opportunity to close the dark geyser, and Kris and Susie are returned to their own world. (The classroom in which Kris and Susie reappear contains several toys and game pieces reminiscent of characters in the Dark World.) Susie then parts ways with Kris, but expresses interest in returning to the Dark World the next day. Kris then has the opportunity to explore the town before returning home and going to bed. That night, Kris, without input from the player, falls out of their bed, rips their soul out of their body, and throws and locks it in a birdcage. Kris then turns towards the screen, revealing that they are in possession of a knife, and that their mostly hidden facial features have been replaced by glowing red eyes and a smile.
Deltarune was developed by Fox in GameMaker Studio. The game introduces a new battle system influenced by the Final Fantasy franchise, contrasting with the original game's combat system (which was inspired by that of the Mother series). Some of the music in the game remixes much of the soundtrack of Undertale, but most pieces are new. The main game uses sounds sampled from EarthBound, while battle music is similar to Breath of Fire III music, and even Lancer's theme is rarely similar to J.A.K.Q. Dengekitai's opening theme. The game also has many similarities with Undertale in the name of characters, for example, Ralsei (one of the main characters) is an anagram of Asriel (a character from Undertale) and Kris (the main character from Deltarune) is almost an anagram of Frisk (the main character from Undertale). The name of the game, Deltarune is an anagram of Undertale.
After previously teasing something Undertale-related a day earlier, Fox released the first chapter of Deltarune, a game "intended for people who have completed Undertale", on October 31, 2018 for Windows and macOS for free. 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. Fox clarified that Deltarune will be a larger project than Undertale and one he anticipates getting a team to help develop and more, and when it is ready, will release the game as one whole package. Fox plans for Deltarune to have only one ending.
- Alexander, Avery. "Review: Surprise spin-off 'Deltarune' is a delight | The Ithacan". theithacan.org. Retrieved 2018-11-15.
- Fox, Toby (November 2, 2018). "Here are my thoughts on Ch 1 of Deltarune. This should answer some questions". Twitlonger. Retrieved December 9, 2018.
- "Kris - Deltarune Wiki Guide - IGN". IGN. Retrieved 2018-11-15.
- Oxford, Nadia (October 31, 2018). "Delta Rune, Like Undertale, Urges You to Show Mercy to Your Foes—But it Doesn't Make it Easy". USGamer. Retrieved October 31, 2018.
- "Hands-on: Undertale creator releases surprise sequel, Deltarune". Gamecrate. Retrieved 2018-11-15.
- Kent, Emma (November 2, 2018). "Undertale creator suggests it's going to be a while before we see more Deltarune". Eurogamer. Retrieved November 2, 2018.
- Wan, Zhiqing (November 1, 2018). "Deltarune: Story and Ending Explained (Spoilers)". twinfinite.net. Retrieved 2018-11-19.
- Kim, Matt (31 October 2018). "Undertale Creator's New Game Also Has an Uninstalling Bug". USgamer. Archived from the original on 18 November 2018. Retrieved 18 November 2018.
But Fox says that they used Game Maker Studio 2's default uninstaller so the problem could lie somewhere else.
- "Deltarune, anagram of Undertale, was released today. We played 84 minutes". App Trigger. 2018-10-31. Retrieved 2018-11-18.
- Fox, Toby. "DELTARUNE". www.deltarune.com. Retrieved 2018-11-02.
- "Cult RPG Undertale gets a surprise spinoff for Halloween". The Verge. October 31, 2018. Archived from the original on October 31, 2018. Retrieved October 31, 2018.
- Frank, Allegra (October 31, 2018). "Undertale creator's new game is Deltarune, a mysterious surprise". Polygon. Retrieved November 1, 2018.