The Genocide Route (also known as No Mercy Route or Vengeance Route ) is one of the main routes in Undertale Yellow , alongside the Pacifist Route and Neutral Route . It depicts Clover killing all possible monsters in the areas of Undertale Yellow 's Underground , with their goal being to defeat Asgore and save the five captured human SOULs .
Its story is different from Undertale 's Genocide Route , giving Clover a different and more blatant motive along with changing some areas completely in terms of direction.
Like in Undertale , the player has to kill as many random encounters as possible in an area to complete the Genocide Route. They have to kill at least 20 random encounters before reaching the end of each of the four major areas ( Dark Ruins , Snowdin , Dunes , Steamworks ). Any minibosses and bosses encountered must be killed, though many will not be encountered. After the kill counter is exhausted, no enemies appear. Periodically past this point, an encounter against no enemy will start with flavor text reading " But nobody came. " and mus_toomuch in the background. However, this does not replace the overworld music like Undertale does and only plays in the encounter.
However, unlike Undertale , once Clover exhausts the kill counter of 5 monsters in one room for the Dark Ruins and Snowdin, or 3 monsters in one room in the Dunes or the Steamworks, encounters can no longer start in that room, signified by a red X appearing over their head. Clover must enter a new room to continue getting encounters.
Clover also does not have a counter at SAVE points allowing them to keep track of remaining encounters. While Flowey states once how many monsters are left after 15 kills in the Dark Ruins, the rest of his SAVE point dialogue is only general comments on Clover's violence that updates every 5 kills. When there are only 7 monsters left in an area, the regular encounter music shifts to Enemy Retreating and slows down with each subsequent monster killed. Once the kill counter is exhausted, the overworld music is slowed down. While the overworld music in Snowdin, the Dunes, and the Steamworks are already slowed down when first entered, they are slowed down even further after exhausting the kill counter there. While it is easier to encounter monsters in Undertale Yellow than in Undertale , Clover's stats are balanced so most monsters need to be shot twice to be killed, prolonging battles.
Clover is still allowed to spare or flee from any monsters. This can be used to get desired amount of EXP by only killing specific monsters. They can also grind G this way, though this becomes unnecessary after exhausting the kill counter in Snowdin, as almost all of the vendors will give out items for free.
While the Genocide Route requires any bosses encountered to be attacked, unlike Undertale , most of the bosses can be skipped by default or by exhausting the kill counter.
The only bosses that are required to kill to progress the route are Ceroba , Axis , and Zenith Martlet . Flowey and Asgore are automatically killed near the end of the route.
The player can abort the Genocide Route either by reaching certain points without exhausting the kill counter or by sparing certain bosses. Any time the Genocide Route is aborted, the overworld music speed returns to normal and Clover returns to their normal expression with their eyes visible again to clarify to the player that the route has been aborted. It should also be noted that Clover's expression and the music also reverts to normal when sparing Dalv, despite the route not being aborted that way.