You've seen damned happy. You've seen sad. You've seen things that toe the line between the two emotions. Now it's time to play the maniac.

The Genocide route is pretty much as it sounds: you need to murder everything in sight. This includes normal enemies and every boss you encounter. If you leave a single enemy alive in an area before leaving, you will be shifted to the Neutral Route; if you Spare any bosses, you will likewise be shifted to the Neutral Route. You will gain a ton of EXP in the process, and become an absolute beast. You’ll also face some different bosses from the Neutral route, and the ending will change.

(Also? People won’t like you on subsequent playthroughs. One in particular, anyway. Just saying.)

In this article we’ll explore what you need to do in each area to stick to the Genocide route. It’s faster than the Pacifist route, to be sure, but it’s also a little more tedious since you need to clear out every area before moving on. The random encounters become fewer and far-between with each fight, so eventually you’re going to be wandering aimlessly for long stretches before you get into a battle. (I recommend getting an audio book or something. Seriously, it’s that bad at some point.)

Think twice before embarking upon a Genocide run. It leaves a mark upon your game that is very difficult to erase, and there will be consequences for any subsequent runs, regardless of how nice you might be in another life.

IMPORTANT NOTICE! I keep getting messages and comments and emails and the like from people who fail their Genocide runs because they move on to the next area before completing their current area. You must kill every enemy in each area (Ruins, Snowdin, Waterfall, Hotland) BEFORE moving on to the next. This also means killing all of the enemies before fighting the area bosses (Toriel, Papyrus, Undyne, and Mettaton). If you try to fight one of the bosses before killing everybody you'll be forced onto the Neutral path.

Nothing special here. You just need to clear out the Ruins before you fight Toriel. It takes a while, but it’ll happen eventually, and it’s pretty easy to boot. ‘Kill’ Napstablook for good measure. You’ll know you’ve been successful when you get a fight that says ‘But nobody came…’ and the music changes. Epic. The battle with Toriel is actually rather surprising, and will let you know you’re on the right path.

As with all later sections, it’s wiser to focus your grinding efforts on later sections of The Ruins, where multiple enemies show up. You’re going for a specific monster kill count, and not just a certain number of battles.

Same deal here: murder everything. There’s a twist, though, because now save points will display how many monsters you still need to kill, in prominent red. If this number disappears you have moved off of the Genocide Route! Be careful not to save if this happens, because you’ve apparently done something very wrong! Linger in the middle sections of Snowdin, before you reach the town, and kill everything before moving on too far. (Try not to fight Jerry. He takes too long to kill physically.)

In addition to the random encounters, you’ll want to kill Doggo, both of the Dogi, the Greater Dog, and Papyrus. Do all of that and you’ll continue along this bloody path.

There are a few changes to this section in the Genocide Path:
  • You’ll automatically skip most of the puzzles. Poor Papyrus.
  • Rather than getting one Snowman Piece from the snowman, you’ll steal three. Ouch.
  • Snowdin Town is empty when you arrive. You can steal 758 gold from the item shop, not that you’ll get much use from it in the future, and as many items as you need. Steal a bunch of Cinnamon Buns for future use. All of the other buildings will be devoid of life. (There’s one person left, mainly because he’s necessary for the next area.)
  • It's possible that the save message telling you how many monsters are left will change to 'That comedian...' while you're proceeding through Snowdin. I'm not entirely sure what triggers it - I think it appeared after a fought Glyde, or at least after speaking to Sans near its cave? - but it will prevent you from seeing how many kills are necessary to clear the area. This does not mean your run is over! Just keep going until Snowdin is clear and you get the terribly-depressing Genocide music.

Yep, murder murder death death. Not much to say here; battle your way through. I found the stretch of land just before the light-casting mushroom section to be particularly good for quickly killing enemies. In addition to the random encounters you’ll want to kill the Glad Dummy (he’s so mad he went all the way around again) and the Monster Kid. Or try, in the latter case.

A few notes:
  • The whispering weeds that are normally so talkative lose their voices. Possibly because you murdered everyone, you monster.
  • Most of the NPCs are gone. There are two exceptions, and oddly enough they’re both vendors. The first is the turtle in the second half of Waterfall; he has lots of extra stuff to talk about, and will put you down at every chance. (But he’ll still sell you stuff.) The other is the TEM SHOP vendor in the Temmie Village; the only difference here is that he doesn’t want to go to college anymore, so you can’t get his awesome armour.
  • No more Thundersnail. Sad face.
When you reach the bridge where you would normally part ways with the Monster Kid, you wind up in the boss fight with Undyne. 

Undyne the Undying. She's one of two major challenges
during a Genocide Run of Undertale.
Undyne the Undying

Y’know how all of the bosses up to this point have not been a challenge? The free ride ends here. Undyne the Undying is one of the the most difficult bosses in Undertale, and because you can’t grind to prepare for her the battle is going to be harsh. Undyne utilizes the same types of attacks she used on the other paths, but the intensity of her attacks is taken to a ridiculous level. You need pinpoint reactions to survive this battle, because there is no way to slow her down. It takes practice and sheer memorization of her patterns to survive, as well as lots of healing items. (Hopefully you still have those Snowman Pieces from earlier. All three are essential.)

Perhaps the wisest thing you can do is purchase the Clouded Glasses from the turtle vendor earlier in Waterfall. Both of these items will increase the amount of time you are invincible after taking an attack, which is invaluable for later stages of the fight when Undyne is really hammering you hard. (The Tattered Notebook also does this, but I recommend keeping the Ballerina Shoes, if you picked them up earlier. They hit harder, and the invincibility effect is not extended by having both the Glasses and the Notebook equipped.) Memorize her earlier attacks - they’re always the same when you play - and slog your way through the final bits, hitting her whenever you don’t have to heal. It takes a while, but you’ll eventually bring Undyne down. 

Having trouble? Here are a few more tips:
  • Attack every round. Don’t do anything else, unless you’re healing. Don’t Check Undyne, don’t waste a turn Sparing her, don’t try to Talk. Fight, Fight, Fight.
  • Save your stronger healing items for later rounds, if possible. The last item you use should, ideally, be a Snowman Piece.
  • Make sure you have at least 20 HP whenever you go into an attack round. If you’re at less than that, heal.
  • This probably goes without saying, but try to maximize your damage every time. You want to cut down on the number of rounds fought as much as possible. In particular, you want to cut down on the later rounds as much as possible, because Undyne just gets harder and harder.
  • Dart colours can be deceptive when they’re moving more quickly, but when the darts are coming in at you slooooowly, focus on the red darts first. Aim towards these. They’re always going to be next in line to hit you.
  • Don’t pay too much attention to the yellow darts unless you really have them down pat. They’re confusing when they come in groups, and can mess you up enough that you miss the normal darts.
  • Move to the sides when the spears are circling in towards you in groups, nudging slightly up and down. Don’t change directions until you’re rammed up against the edge of the box, and even then, try and time it so the spears are at their widest point before you turn around.
  • Practice the spear-chucking sections in particular. Eventually Undyne will give up on the darts and focus solely on the spears, and if you can survive this long and know how to avoid the spears, you’re good to finish the fight.
  • Despite what I’ve read online, I don’t recommend using Sea Tea in this fight. It increases your speed, which seems like a good thing, but I find it’s better to stick with a consistent pace. You don’t need to be moving at full throttle to avoid attacks - you just need to know in which direction you should nudge your heart.
Yep. Hard-as-hell fight, and it will probably require a few hours of practice to beat. You get two levels for winning, though, so… that’s pretty sweet, right?

Forty? Great Zeus. You’ll be wandering ‘round these parts for a while, so get used to it. The bridge next to the final door of the Core is probably the best place to grind enemies, as they appear relatively often here and offer the best experience in the region. In addition to the random enemies you’ll have to kill the two Royal Guards and Muffet to continue along the path of Genocide. (You do not have to kill So Sorry. Don't worry about him.)

There are a few changes to Hotland when you wander down the lonely paths of Genocide:
  • You will not see Dr. Alphys. Ever. She's mentioned, but she's effectively removed from the game in these runs.
  • The laser traps have been deactivated, the puzzles are already cleared, and Mettaton will not bother you. All of the elevator destinations are already unlocked, as well, so that’s a time saver - though many of them are blocked by lasers, making the trip to the end substantially shorter.
  • The vendors to the right of the MT Resort are gone. You can steal 5 gold from their till and anything you like from their store.
  • The MT Resort itself is largely empty, but the dude who runs the MTT Burger is still there, and he sells the same stuff. He just has different things to say.
  • You can skip the majority of the Core by using the elevator from the entrance. 
  • Mettaton takes on a new form in the final battle of the Core, that of Mettaton NEO. It looks to be an epic fight… but… yeah. Oh well. Unlike on most runs, you can backtrack to other locations after beating him. You nevertheless get several levels for winning. Don't mess around in the menu during this 'fight', or it's possible Mettaton will decide that you aren't evil enough, and your run will switch to Neutral.
Once you’ve slaughtered your way through Hotland, you’ll find a loooong section of story dialogue with Flowey waiting. And when you reach the hall before the Throne Room…

Sans, the final boss in a Genocide run of Undertale.
He is made of pain and fart jokes.

Sans is not just a boss. He's not even a super boss. He is an unfair boss, an omnipotent boss, a boss-to-end-all-bosses boss. There is no doubt whatsoever that he's the most difficult challenge you'll face when playing Undertale, because he doesn't play by the rules. And you're going to suffer for a long, long time if you decide you absolutely must defeat this guy. He's basically there to stop you from ruining your life.

Sans is similar to his brother Papyrus in that he uses bone-based attacks to do a lot of his damage. The difference between the difficulty of the two is of a ridiculous magnitude, however, and you'll be forced to pull out every trick in the book to beat him. Sans is a horrifying cheater, and he'll use the following feats of bastardry to defeat you:
  • He begins the battle by attacking. Immediately after his monologue he'll launch into a four-part attack that can easily kill you before you get the chance to do a damned thing. Memorizing this pattern is key to getting off on a good foot, and after a few goes you'll probably be able to get past it without taking damage.
  • Sans has a single hit point. That said, he will dodge every one of your attacks until very late in the fight. This is a scripted fight that will last roughly the same amount of time, every time you fight it. You still need to try and hit Sans, though, because he'll start repeating attacks until you exhaust his dialogue options.
  • All of Sans' attacks deal one point of damage. Just one! That said, they deal poison damage, which will slowly drain away a larger percentage of your health, during pauses in the menu, no less. They also ignore invincibility flashing. Assume that every time you get hit, you will not receive a temporary reprieve. You won't.
  • The vast majority of the battle has you contending with gravity as a blue heart. There's a lot of platforming to do. Note here that you can hop through the platforms Sans' summons, which will help you through some of his attacks.
  • There are several sections where Sans will throw you against walls and immediately summon bones to inflict damage. You can use his hand motions to figure out where he's going to throw you, giving you a bit more of an edge than waiting for red damage zone boxes to flash on the screen. Mind that you need to move in the opposite direction of his hand signals.
  • Late in the fight Sans will cut out the screen for brief flashes and then launch attacks. You need to know where these attacks are going to appear before they do, or you're going to take damage. These are somewhat random, mainly in what order he uses them, though the nature of the attacks is always the same.
  • At one point Sans will offer Mercy. When this happens you can take the opportunity to heal yourself and not have to worry about another attack immediately after. Don't opt for Spare, though, because he'll murder you. (Though it's pretty funny to watch him do this at least once.)
  • Also late in the fight, Sans will become the cheapest bastard ever and deploy attacks while you're in the goddamned menu. Bones will wander along the bottom of the screen, and another will be ready to hit you if you enter a menu. Spend as little time as possible meandering about the menu when this happens. (If you can get this far in you hopefully don't need healing items anymore anyway.)
You need to memorize Sans' pattern to stand a chance. Just having good reflexes is not enough. Having lots of healing items is wise, as well, though only if you can consistently avoid taking damage more than once or twice per round. I highly suggest watching this YouTube video of the fight if you need to figure out what to do during a given round, though this can't really substitute for practice. You'll probably fight Sans a hundred times or more before you get a really good bead on everything he can do. Good luck.

(Also, if it's not obvious, you need to drag the box over to Fight once Sans falls asleep in order to finish him off. It will take quite a while once Sans stops attacking for this to happen, so, be patient.)


I won't spoil what happens once you've beaten Sans and moved on, but the rest of the Genocide route is pretty straightforward - at least until the very end. You'll be treated to a blank screen whenever you reload the game, and you'll seemingly be stuck there for eternity. This is not the case, however, as you'll eventually be given an offer to restore your game. This is the only way, short of messing with your file settings, to return Undertale to working order... though you'll also permanently change the ending of the Pacifist route. It's, ah, slightly less happy. Still, you asked for it...