Genocide Route

"If you keep going the way you are now... You're gonna have a bad time."

- Sans in Snowdin Forest The Genocide Route (sometimes called the No Mercy Route) is a event leads to one of the three main endings of Undertale. It consists of the player to killing every single monsters in the Underground.

Method
The Genocide Route occurs when the protagonist kills every enemy in every region: the Ruins, Snowdin Forest, Waterfall, and Hotland. (The CORE is a sub-region of Hotland.)

Starting in the Ruins, the protagonist intentionally triggers encounters and kills monsters until encounters with monsters no longer occur; this is similar to level-grinding in other RPGs. After killing all monsters in an area, encounters still occur, but monsters do not appear. In a font size smaller than usual, the battle text reads "But nobody came.", which can also occur in a Neutral Route when you kill all monsters in an area.

After the protagonist sees this message, the music for the area changes to a distorted ambient track. This track is a .08x speed version of a part of "Your Best Friend." After exiting the Ruins, all overworld songs are lower pitch, slower versions of their Neutral and True Pacifist Route counterparts.

If the protagonist stops meeting the requirements for a Genocide Route at any point, they revert to a Neutral Route where the unaltered soundtrack plays. NPCs still occur in the region where the protagonist abandoned a Genocide Route.