Genocide Route: How to Kill Everyone

How to cleanse the underground of all monsters.

Disclaimer

WARNING: The Genocide route is not for players who are new to Undertale. You are strongly discouraged from doing a Genocide run for your first playthrough. Crucial plot elements and gameplay will be radically altered in ways that won't make sense without the context that a normal run gives.

This guide contains early-game spoilers.

What's the Genocide route all about?

Doing a Genocide run entails killing every possible monster through a specific series of actions. Sparing can NEVER be done on major characters at any point. Using Spare to successfully end a boss fight (or a non-recurring fight, such as Greater Dog) will immediately invalidate a Genocide run. It's recommended that you never Spare period, though.

Going on a genocide crusade will introduce innumerous changes to Undertale's plot and gameplay, providing a morbidly unique experience for anyone determined enough to go forward with it.

This guide will cover how to begin a Genocide run and maintain it to the grisly end. This guide will not cover tactics for enemies, help you "make the right choices", or otherwise dictate your playstyle.

Starting your Genocide Crusade™

1. After waking up in the Ruins, progress with the game as usual until you reach the room with a Save Point in the leaves. This area allows the player to have random encounters with monsters.
   
2. Stay in this room and walk around to grind random encounters. Whenever you trigger a random encounter, kill all monsters. As you continue to grind, the random encounter rate will gradually drop until you're only getting around one encounter every minute.
   
3. Continue grinding encounters in this area until you get the encounter below:

By getting this encounter, you have initiated the Genocide route. You are now free to continue through the Ruins, murder Toriel in cold blood, and continue onto the rest of the underground.

Persevering in Your Murderous Rampage

Although you've probably already noticed quite a few changes, the real fun of Genocide mode begins in Snowdin. Don't let yourself get off track, though; you will need to repeat the grinding process in every major area. That means you need to get the "But nobody came" message in Snowdin, Waterfall, and Hotland. Failing to do this will invalidate a Genocide run.

It's strongly recommended that you grind random encounters ASAP after entering a new area, as your Genocide run will be rendered null if you venture too far ahead without exhausting that area of random encounters.

Extra Tips

• From Snowdin onwards, Save Points will tell you how many more monsters need to be killed in that particular area. When an area has been exterminated, Save Points in that area will say "Determination."
  
• Hotland + CORE count as a single area for the purposes of a genocide run, so you can use the scripted encounters in CORE to your advantage so long as you DON'T fight the boss before exhausting encounters.
  
• Alt+Tabbing out of Undertale while moving makes you run in place while tabbed out, letting you do other stuff while the main character hunts for random encounters.
  
• Explore! Almost everything is different in a Genocide run, both to your benefit and detriment.
  
• Try your best to have a good time.

[Peppermintgirl21]

you can also Frisk Dance to grind monsters easily :DDDDDDD

[I_Teleported_Bread!]

░▄ ▀▄▄▀▄░░░░░░░░░ This is Toby.
░█░░░░░░░░▀▄░░░░░░▄░Toby wants to take over Steam.
█░░▀░░▀░░░░░▀▄▄░░█░█He needs your help.
█░▄░█▀░▄░░░░░░░▀▀░░█Copy/paste Toby to help him.
█░░▀▀▀▀░░░░░░░░░░░░█If not, he will use the Legendary Artifact's power.
█░░░░░░░░░░░░░░░░░░█On you.
█░░░░░░░░░░░░░░░░░░█And you now you just going to D I E
░█░░▄▄░░▄▄▄▄░░▄▄░░█░:tobdog::tobdog::tobdog::tobdog:
░█░▄▀█░▄▀░░█░▄▀█░▄▀░

[Moon Pie (Tropical Fruit Flavor)]

don't kill papyrus off in the thumbnail

[0x]

instead of alt tab, walk up and press both up#down key at the same time. you character will move weirdly upon reaching the top and this will spawn remaining monsters fairly quickly

[damparmpits]

paperos?

[Untrustful]

alt+tab doesnt work for me :(

[Horror]

I did the same thing as @Knuff L

[Eldritch Kitsune]

@Spatula
ik im late but it is true.
Completing a True Pacifist route after selling your soul, the final shot of the ending will be altered. Whenever or not you consider this its own ending though is up to debate.

[Spatula]

@Knuff. apparently when you do genocide it changes all of your pacifist routes slightly, im not sure if its true but i heard it somewhere.

[professeurchoron]

very helpfull