Undertale is a role-playing video game created by American indie developer Toby Fox. Players control 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 a quest to return to the surface, mainly through the combat system; the player navigates through mini-bullet hell attacks by the opponent, and can opt to pacify or subdue monsters in order to spare them instead of murdering 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, with only additional art created by other artists, primarily Temmie Chang. The game was inspired by the Mother and Mario & Luigi role-playing series, the bullet hell shooter series Touhou Project, and the British comedy show Mr. Bean. Undertale was initially meant to be two hours in length and was set to be released in mid-2014, but development was delayed over the course of the next three years.
The game was released for Microsoft Windows and OS X in September 2015, for Linux in July 2016, for PlayStation 4 and PlayStation Vita in August 2017 and for the Nintendo Switch in September 2018. The game was acclaimed for its writing, thematic material, intuitive combat system, musical score, and originality, with praise directed towards its story, dialogue, and characters. The game sold over one million copies and was nominated for multiple accolades and awards, including Game of the Year from several gaming publications and conventions. The first chapter of a related game, Deltarune, was released in late 2018.