Undertale is a Role-Playing Game by Toby Fox, released on September 15th, 2015. Its development was the result of a Kickstarter campaign that raised $51,124note . The game and a demo are available on its main website here, and trailers can be viewed here and here. A port for the PlayStation 4 and Play Station Vita was released on August 14, 2017, while a Nintendo Switch version was released on September 18, 2018 and an Xbox One version was released on March 16, 2021.
Long ago, humans and monsters lived in harmony, but eventually that peace gave way to war between the two species. The humans emerged victorious and sealed the monsters underground Mt. Ebott with a powerful spell, where they reside to this day.
The game tells the story of a young child who investigates a mountainside cavern in Ebott and falls down a deep hole, awakening on a bed of flowers in a dark and mysterious place. Now the child must find a way back home, encountering all manner of creatures along the way, ranging from friendly to hostile. Unfortunately for the child, King Asgore, leader of the monsters, desires their soul to break the monsters free, and has ordered his minions to capture them. And as the child soon learns, there is far, far more to this tale than it seems...
Undertale borrows heavily in atmosphere from the Mother trilogy, and uses combat mechanics similar to Bullet Hell games, where you must dodge enemy projectiles and protect the heart-shaped avatar representing your SOUL. The game's story changes significantly depending on how you deal with the monsters you encounter: you can fight and kill them to earn EXP and increase your LV, or figure out how to befriend them and show them mercy. Notably, Fox has cited the Cult Classic Moon: Remix RPG Adventure as a major inspiration for these elements. Fox has also cited the Shin Megami Tensei games as an inspiration for the game, specifically its demon negotiation.
On October 31, 2018, the first chapter of the "sister game" (as in, not exactly a sequel) game Deltarune was released for free for Windows and macOS. It can be downloaded here.
In September 2019, both the character of Sans (in the form of a Mii Costume) and a remix of the game's Signature Song, "Megalovania", were added as DLC for Nintendo's Super Smash Bros. Ultimate.
Not to be confused with the similarly-named Underrail. Despite both games being set underground, Underrail homages a different sub-genre of Role-Playing Game.
See also LISA, OMORI, Jimmy and the Pulsating Mass, and Annventure, other EarthBound-inspired RPGs with dark atmospheres.
Before reading the tropes section or other sections, please note that by its very nature, Undertale is very difficult to talk about at length without spoiling it. Read with care.
(Seeing all these tropes present in Undertale... it fills you with determination.)