Several gaming publications and conventions listed Undertale as game of the year, and others have since listed it as one of the greatest video games.

The game sold over one million copies and was nominated for multiple accolades and awards.

The game was acclaimed for its thematic material, intuitive combat system, musical score, originality, story, dialogue, and characters. It was also ported to Linux in July 2016, PlayStation 4 and PlayStation Vita in August 2017, the Nintendo Switch in September 2018, and Xbox One in March 2021. The game was released for OS X and Windows in September 2015. However, development was delayed over the next three years. Originally, Undertale was meant to be two hours in length and was set to be released in mid-2014. The game took inspiration from several sources, including the Brandish, Mario & Luigi, and Mother role-playing game series, bullet hell shooter series Touhou Project, role-playing game Moon: Remix RPG Adventure, and British comedy show Mr. Outside of artwork and character designs by Temmie Chang, Fox developed the entirety of the game by himself, including the script and music. These choices affect the game, with the dialogue, characters, and story changing based on outcomes. They can opt to pacify or subdue monsters in order to spare them instead of killing them. The combat system involves the player navigating through mini- bullet hell attacks by the opponent. The player meets various monsters during the journey back to the surface, although some monsters might engage the player in a fight. The player controls a child who has fallen into the Underground: a large, secluded region under the surface of the Earth, separated by a magical barrier. Undertale is a 2015 2D role-playing video game created by American indie developer Toby Fox.

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