Undertale - No Mercy is a series of three creepypastas created by .mynameischrome., who is the founder and owner of Creation Wiki.
- Undertale - No Mercy is the original version of the creepypasta and the first installment in the series. The creepypasta is not favored by its creator. Undertale - No Mercy is about a person who discovers a beta version of Undertale in which everything seems more morbid and disturbing. This is not canon to the timeline started in the next installment.
- Undertale - No Mercy (Revised) (or Undertale - No Mercy II) is a revised version of the original Undertale - No Mercy. This version differs heavily from the original, but still keeps some core aspects. This creepypasta is about a normal man named Adam who has a gamer and coder friend named Mike. Mike shares with Adam a download link to a secret version of Undertale that he found in the original game's code. Adam plays it on the Pacifist and Neutral routes, and after seeing nearly nothing different, he decides to play the Genocide Route.
- Undertale - No Mercy: My Friend Adam is an upcoming creepypasta, the third installment in the Undertale - No Mercy series and the second installment in the canon timeline of events. In this creepypasta, Mike talks about Adam on an Undertale datamining forum, seeking help. The creepypasta will be released in late 2016.
- Undertale - No Mercy: The Final Mystery is the final installment of the Undertale - No Mercy series. It will be released in late 2016 or sometime 2017.