If certain events are triggered before clearing an area completely of monsters, the protagonist is automatically sent back to the Neutral Route. Kill counters for different areas have different requirements.

Undyne the Undying (triggered by fighting Monster Kid).

Lesser Dog (random but mandatory encounter).

All mini-bosses (excluding Napstablook, Snowdrake, and Lesser Dog and including Shyren) can be encountered even after the kill counter is exhausted, which can be used to obtain extra EXP.

Kill every boss and miniboss (Secret bosses So Sorry and Mad Mew Mew are not accessible, and Glyde is optional).

Once the protagonist satisfies the kill requirement, SAVE Points display the message ' Determination.'.

However, they are both scripted to appear in at least one random encounter unless they are skipped using glitches.

Snowdrake and Lesser Dog are unique in that they must be killed before the kill counter is exhausted and are also part of the kill counter.

New Home: No kills (Sans The protagonist automatically kills Asgore upon encountering him, while Flowey is killed when any of the action buttons are pressed.).

Waterfall: 18 kills ( Undyne the Undying).

The following is a table of the number of random encounters only that the protagonist must kill as stated at SAVE Points in red text, followed by the final boss of the area.

The protagonist can also spare certain monsters so that they can kill monsters that offer more EXP and GOLD, such as Glyde.

Sparing certain monsters allows the protagonist to avoid fighting particular monsters such as the high-defense Jerry.

The protagonist can spare any number of random encounters ( Snowdrake and Lesser Dog are exceptions, as seen below).

Encounters become increasingly harder to find as the protagonist grinds out the kill counter for each area (except New Home, in which they are scripted).

This requirement must be done before approaching the final encounter of that area.

Exhaust the random monster kill counter in every region.

The first SAVE Point in Snowdin Forest displays the kill counter for the first time.

NPCs still occur in the region where the protagonist aborted the Genocide Route. 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. This track is a part of Your Best Friend playing at 1/13th speed (~0.077x or ~92% slower) with added reverb.ДЄfter exiting the Ruins, most overworld songs are lower pitch, slower versions of their Neutral and True Pacifist Route counterparts. In a font size smaller than usual, the battle text reads ' But nobody came.', which can also occur in a Neutral Route after killing all monsters in an area.ДЄfter the protagonist sees this message, the music for the area changes to a distorted ambient track, mus_toomuch.ogg. After killing all monsters in an area, encounters still occur, but monsters do not appear. 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. 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). Battle text after the protagonist exhausts the kill count.

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