A Step-by-step Guide to the Genocide/No Mercy Route

To start, one must first understand the basic premise of the No Mercy route:
The objective is to kill as many monsters as possible, exhausting the 'Kill Count' of each area, and leveling up.

Importantly, fighting the boss will lock you out of encountering any more monsters in the area, meaning you must kill everyone before fighting the boss of the area.

Now, let's cover a few misconceptions, as with Undertale (and the No Mercy route in particular), there are quite a few.
Here are the big ones:

• Getting a certain amount of EXP and LV is not required; depending on your actions, you can accrue varying amounts of either and still finish the No Mercy route. All that matters is killing everything.
• The name 'Chara' is not required for the No Mercy route.
• Sparing most regular enemies is perfectly acceptable. There are certain enemies you have to kill upon encountering, but those are the exceptions, rather than the rule.

Now, 'killing everyone' in an RPG with random encounters may seem strange: how can you kill 'everything' if there isn't a limit on the monsters you can encounter?

Well, simple.
There is.

Each area has a 'Kill Count':

The Ruins has a Kill Count of 20, Snowdin has a Count of 16, Waterfall has 18, while Hotland and the CORE share a Kill Count of 40.
Each monster Certain monsters, namely bosses, mini-bosses, and special characters, do not contribute to any Kill Count; these exceptions will be covered when they come up. you kill contributes to the Kill Count.

Once you've exhausted the Kill Count, further encounters will be replaced Notably, it's possible to kill more monsters than the Kill Count implies; for example, by encountering two monsters at once while the Kill Count is at 1 left, you'll be able to kill one more monster than usual (this doesn't do anything, mind you). by an empty screen; seeing this screen is a good way to double-check whether you've successfully killed everything.

Obviously, exhausting the Kill Count requires a fair amount of grinding, which can be pretty tedious if you don't know what you're doing.

A key concept to understand is that, after getting an encounter in a room, the next encounter takes significantly longer to appear.

By leaving and re-entering the room, you reset the 'Step Count' to the next encounter, which saves an immeasurable amount of time over the course of the game.

Additionally, by holding Up and Down at the same time (really only possible on a keyboard), you can preform a glitch (exploit?) which causes Frisk to repeatedly walk up and down against an upper wall.

This counts as movement, and progresses the Step Count to the next encounter. A misconception among many fans is that this speeds up getting encounters. It doesn't; it only makes it easier to keep moving.

Now, on to the route itself.

The Ruins, with a Kill Count of 20, start off the route with less of a bang and more of a honk of despair, introducing The Player to the tedium of grinding for kills.

The first Froggit encountered in the Spike Maze room does not contribute to the Kill Count, nor is it required to kill to continue, but it's best to kill it regardless: it gives 10 EXP and 20 GOLD, much more than the average Froggit.
Picking on Loox can also net you some more EXP, if you need it.

Napstablook also doesn't count towards the Kill Count, and can even be SPARE-d. Do note that when Napstablook is defeated via violence and awards '-1 Experience Point', it doesn't actually affect your EXP.

If you've already exhausted the Kill Count before encountering Napstablook, they'll simply dissappear upon approach; if you don't feel like fighting them, exhaust the Kill Count beforehand.

Toriel is the boss of the Ruins, and so you'll stop encountering monsters upon defeating her, either by killing her or SPARE-ing her.
This means you'll have to exhaust the Kill Count before progressing.

To be clear, you can enter her home, get the pie, and even encounter her, Most interestingly, because Toriel contributes to the Ruins Kill Count, it's possible to exhaust it by killing her, which still allows you to continue the route!
I was surprised too, but it's the truth!

Notably, because you haven't yet exhausted the Kill Count when you fight her this way, you're also not yet on the No Mercy route, so she doesn't die in one hit, nor does she do her unique dialogue. Again, this still allows you to continue the route, despite what common sense may imply. before going back to grinding and proceeding with the No Mercy route.

Anyway, it's probably best to grind in the Perspective Puzzle's last room: it's the last room with encounters, it's right next to where you get the Toy Knife, and the SAVE Point in front of Toriel's house is right next-door.

Once you've exhausted the Ruins Kill Count, head to Toriel's house, grab the Pie by sleeping in the bed, and tell that G.O.A.T. to G.T.F.O.!

Oh, and before you leave, you might want to stock up on Spider Cider after killing Toriel; of all of the infinitely obtainable consumables, Spider Cider heals the most HP until you can get Legendary Heroes from the MTT Resort.

Moving into Snowdin, you'll finally be shown the Kill Count in-game (ex; '16 left.') whenever you SAVE.
Upon exhausting the Kill Count, it'll say 'Determination.', Contrary to popular belief, this line is not highlighted in red. which can be used as a benchmark to know you're finished grinding.

Snowdin has a Kill Count of 16, but numerous monsters do not contribute to the Kill Count, and/or have special conditions:

Unlike other random encounters, Lesser Dog must be killed; do not SPARE or FLEE from Lesser Dog, nor the rest of the Canine Unit. Lesser Dog does contribute to the Kill Count, however.

Doggo, Dogamy, Dogaressa, and Greater Dog all must be killed, although they don't contribute to the Kill Count.

Jerry is a near unmissable encounter, and does contribute to the Kill Count, but killing it may be annoying; Jerry takes 10 hits to kill.
It's best to SPARE Jerry unless it's your last kill, especially given it's low EXP rewards.

Glyde also contributes to the Kill Count, but unlike Jerry, they're worth quite a lot of EXP, meaning they might be worth the kill despite the effort required to encounter Glyde can be encountered in the Mysterious Place, but the room has a very high Step Count, meaning it takes several minutes on end to encounter them.

Importantly, unlike all other encounter functions in the game, the post-battle Step Count of the Glyde Encounterer [sic] is lower than its pre-battle step count, meaning it's actually faster to stay in the room after encoutering them.

This is likely because of how the code is copied from the Gyftrot Encounterer and Snowdin Encounterer.
As an aside, the encounter functions are actually very interesting; I might make a write-up on that sometime in the future. them.

Now on to the 'point of no return' here:

Defeating Papyrus Notably, unlike Toriel, Papyrus does not contribute to the Snowdin Kill Count, so killing him with '1 Left' does not allow you to progress through the No Mercy route. is what prevents Snowdin encounters, so he's the point of no return.

Do note that encountering him is fine.
When you die to Papyrus, you are simply thrown into his shed, without getting a proper Game Over.
Once you exit the shed, you can resume grinding at your leisure.

The point of no return is defeating him, either by SPARE-ing him or killing him.

To be clear, it's perfectly fine to enter Snowdin Town, SAVE, buy from the shop, chat with the locals, and lose to Papyrus, even if you haven't exhausted the Kill Count.
In fact, entering Snowdin Town and then going back to grind in the Gauntlet of Deadly Terror is actually the preferred way to grind in Snowdin, as it has a relatively low Step Count and is right next to the SAVE Point.

You have to leave and re-enter the Gauntlet of Deadly Terror at least once for encounters to resume after the cutscene, anyway.

Once you've killed Papyrus, head into Waterfall, but not before getting a few Cinnamon Bunnies (stolen from the Snowdin General Store), in addition to your collection of Spider Cider. In the box, you should have about 7 of them combined.

Also make absolutely sure to get the Snowman Pieces from the Snowman partly through Snowdin; the Snowman doesn't contribute to the Kill Count or anything, but the healing will be useful for later.

Waterfall has a Kill Count of 18, and has numerous scripted encounters.
Despite this, there's little to nothing to keep in mind; just kill everything you come across, as there's no enemies worth saving for later.

Do remember to pick up the Dusty Tutu and Ballet Shoes, as they have good STATs for your purposes.

It's best to grind in the Echo Flowers Hallway between Gerson's shop and the Mushroom Maze, as it has the lowest Step Count of any of the rooms this far into Waterfall. Don't worry about the point of no return here; the game outright tells you when you shouldn't proceed.

With that, you should be golden until Hotland.

If (and only if!) you need any more help for the remainder of Waterfall, click here.
Don't worry, you'll know it when you need some help.

Unlike other areas, the CORE is considered a sub-area of Hotland, and therefore shares its Kill Count of 40 with the rest of the area.

This time, the point of no return is the cutscene where Mettaton confronts you right after entering the door at the end of the CORE Bridge. By taking the elevator at the entrance of the CORE, you'll end up right next to the doorway.
Although you can technically enter the room without triggering the cutscene, it's very easy to do so accidently, so you shouldn't head in until you've exhausted the Kill Count.

In Hotland, RG 01, RG 02, and Muffet are the three encounters to keep note of. Like the Canine Unit, you must kill them to proceed with the No Mercy route, and they don't contribute to the Kill Count.

You might also want to pick up the Instant Noodles from Alphys's fridge - in certain situations, it can heal for up to 90 HP.

Aside from that, don't worry about anything else in Hotland Proper; the CORE is where the route really continues.

The best place to grind is at the right side of the CORE Bridge, right outside of the SAVE room before Mettaton's Stage.
Once you've hit 7 left, head to the Warrior's Path to get into the scripted encounters there; this will save some time by not having you grind for more encounters at such a low Kill Count.

Once you've exhausted the Kill Count, try your hand at fighting Mettaton.
If you fail, here's a guide: Geno Boss Guide 2.

With Mettaton out of the way, all that stands between you and the ending you've worked so hard for is the Castle.

Take the elevator out of the CORE, traverse the Castle, and proceed through to the Judgement Hall. Technically, it's called the Last Corridor; 'Judgement Hall' is a fanon name.

You likely already know what's next.
Let's get to the point.

Here's the guide.
Geno Boss Guide 3

Well, THAT happened! XP

Now that you've finished the game and destroyed the world, there is yet more to discuss regarding the No Mercy route, even barring lore, gameplay opinions, and thematic importance.

In particular, the whole 'destroyed the world' thing wasn't a joke.
It's well and truly gone, and even redownloading the game won't do a thing.

All you're left with is a black wind, and all you can do is wait... ...for ten minutes.

(You have to wait on this screen for 10 minutes)

'Give it to me.'
'And I will bring this world back.'

'Yes'

'Then it is agreed.'
'You will give me your SOUL.'

'Yes'

Agreeing to their proposition will bring the world back, but at a cost.
Obviously, that cost is your SOUL; the very culmination of your being!

From now on, all future playthroughs of either the True Pacifist route or the No Mercy route will have their endings altered, with no way to change them back.

Finally, we get to the technical details.
If you're a purely casual player, feel free to stop reading; there's nothing here for you anymore.

So, what about your SAVE File?

Upon destroying the world (and before bringing it back), your SAVE File is deleted, and in its place is system_information_962.
When you launch the game with this file in the SAVE directory, you get the black screen forcing you to wait ten minutes.

Upon bringing the world back, system_information_962 is deleted, and system_information_963 is created in its place.
This is the file that allows the game to remember if you've done the route before - no matter how many times you complete it or what you do to your SAVE File, this file is never removed That is, until you do another No Mercy route, which temporarily replaces it with system_information_962 again. by the game itself.

To restore your SAVE File, go to Undertale's SAVE directory
(C:\\users\USERNAME\AppData\local\UNDERTALE\), and delete system_information_962 or system_information_963, whichever is present.

If you don't know how to get there, hold WIN and press R, type %localAppData%\UNDERTALE in the search bar, and click Okay.

Oh, and by the way, the contents of the files are irrelevant - only their presence matters.
All they say is 'a' for system_information_962 and 'b' for system_information_963. The files have no extensions though, so you'll have to manually open them with a text editor to see this.

Murder Level

Progress through the No Mercy route is tracked by a variable called the 'Murder Level'.
It's an entirely under-the-hood statistic that increases to a given value if all previous criteria For example, let's say Murder Level 1 requires condition 1, Level 2 requires condition 2, etc.

If you've fulfilled conditions 1-3, you'll be at Murder Level 3.

From here, if you fulfill condition 5, but don't fulfill condition 4, you'll still be at Murder Level 3.

If you then complete condition 4, you'll immediately jump to Murder Level 5. have been fulfilled.

The conditions for each Murder Level are as follows:

• Murder Level 1: The Ruins Kill Count is at least 20 Specifically, global.flag[202] >= 20
• Murder Level 2: Toriel is dead Specifically, global.flag[45] = 4
• Murder Level 3: Doggo is dead Specifically, global.flag[52] = 1
• Murder Level 4: Dogamy is dead Specifically, global.flag[53] = 1
• Murder Level 5: Greater Dog is dead Specifically, global.flag[54] = 1
• Murder Level 6: Snowdrake is dead Specifically, global.flag[57] = 2
• Murder Level 7: The Snowdin Kill Count is at least 16 Specifically, global.flag[203] >= 16
• Murder Level 8: Papyrus is dead Specifically, global.flag[67] = 1
• Murder Level 9: Shyren is dead Specifically, global.flag[81] = 1
• Murder Level 10: Glad Dummy is dead Specifically, global.flag[252] = 1
• Murder Level 11: The Waterfall Kill Count is at least 18 Specifically, global.flag[204] >= 18
• Murder Level 12: Undyne is dead Specifically, global.flag[251] = 1
  &&
  global.flag[350] = 1
• Murder Level 13: The Royal Guards are dead Specifically, global.flag[402] = 1
• Murder Level 14: Muffet is Dead Specifically, global.flag[397] = 1
• Murder Level 15: The Hotland Kill Count is at least 40 Specifically, global.flag[205] >= 40
• Murder Level 16: Mettaton is dead Specifically, global.flag[425] = 1
  and the 'Redemption Flag' hasn't been set Specifically, global.flag[27] = 0

The 'Redemption Flag' is a flag Specifically, global.flag[27] in the code that is set to 1 when certain monsters are spared.
The Redemption Flag is checked at various points throughout the game, like before Undyne the Undying and Mettaton NEO.
If the Redemption Flag has been set to 1, it'll prevent you from progressing through the route, making it necessary to kill the monsters that set it, even aside from the direct requirements of the Murder Level.

The following monsters, when spared, trigger the Redemption Flag:

• Toriel
• Doggo
• Lesser Dog
• Dogamy
• Greater Dog
• Papyrus
• Shyren
• Glad Dummy
• Monster Kid
• RG 01
• RG 02
• Muffet

You may note several oddities here:

Toriel, Doggo, Dogamy, Greater Dog, Papyrus, Shyren, Glad Dummy, RG 01, RG 02, and Muffet all trip the Redemption Flag, despite already being required to progress the Murder Level.
Monster Kid also trips the Redemption Flag, even though SPARE-ing them means you can't fight and kill Undyne the Undying, which is already required for Murder Level 12.

SPARE-ing Dogaressa does not trip the Redemption Flag, similar to how Murder Level 4 only tracks if Dogamy is killed.
To be fair though, as Dogamy and Dogaressa can't be killed or spared without the other, it does make sense to only pay attention to one of their states.

On the other hand, the Royal Guards, despite always being spared together, each set the Redemption Flag independently.
To make things even more weirdly redundant, RG 01 and 02 do share a kill state, that being global.flag[402].

With all of that in mind, the Redemption Flag is actually more of a super late check to see if you've killed Lesser Dog, seeing as how every other monster to set it doesn't actually need to in order for the No Mercy route to function correctly.

The Redemption Flag isn't completely useless though, as it does affect things like dialogue and NPCs disappearing (which we won't get into here because it's way too much work to document).

Now that we understand the Murder Level and how it's set to various values, what does it actually do?

Well, again, I won't get into all of the minute differences here, but I will mention some notable interactions that are dependent on the Murder Level and/or Redemption Flag:

Murder Level 1 is what sets Toriel's DEF to -9999, allowing you to kill her instantly.

Murder Level 2 is what allows you to take three Snowman Pieces from the Snowman, and see the Kill Count at SAVE Points.
It also forces an encounter against Lesser Dog for the third random Snowdin encounter, meaning it isn't possible to simply miss Lesser Dog.

Murder Level 3 causes the Nice Cream Guy to disappear for the rest of the game, provided the Redemption Flag isn't set.
Exhausting the Snowdin Kill Count also does this, even when the Redemption Flag is set.
The same conditions also cause the Snowdecahedron to have different dialogue, and, interestingly, cause the game to check the state of the No Mercy route.

Murder Level 3 (along with Murder Level 4 for the XO Switch Puzzles) is also what tells the game to pre-solve the puzzles throughout Snowdin, provided the Redemption Flag isn't set.

If the Murder Level is exactly 5 when the Snowdin SAVE Point dialogue appears, then the text will read: "*That comedian...", provided the Kill Count hasn't been exhausted.
This is to remind you to kill Snowdrake, as he's required to be killed to progress the No Mercy route.

Murder Level 6 does...
...basically nothing - its only purpose is to track if Snowdrake has been killed.

Murder Level 7 is what causes all the Snowdin Town NPCs to disappear (aside from Monster Kid).
This includes the Ice Wolf, who no longer throws ice into the river.
The dissappearance of Snowdin Town NPCs is unnaffected by the Redemption Flag.

Murder Level 7, like Murder Level 1, is what allows you to one-shot Papyrus. At this point, if you SPARE Papyrus, Sans'll have different dialogue at his station in Waterfall.
This still prevents you from going out to Grillby's with him, though.

Murder Level 8 changes the exclamation point icon to a smiley face icon upon encountering an enemy, and pre-solves most puzzles in Waterfall.

Murder Level 12 is what changes Hotland and the CORE, slowing their music, and allowing you to one-shot Muffet and the Royal Guards.
Additionally, getting a Neutral ending with a Murder Level equal or higher than 12 is what gives you the Alphys ending, so killing Undyne the Undying guarantees that ending provided you don't finish out the No Mercy route.

• Murder Level 15 is the final relevant check for the No Mercy route; it's what allows Mettaton NEO's dialogue to progress normally and finish out the route.
  Killing Mettaton NEO at Murder Level 15 sets the protagonist's EXP to 50,000, gives different dialogue, At Murder Level 15, he says:
  'GH...'
  'GUESS YOU DON'T WANT TO JOIN MY FAN CLUB...?'
  
  At Murder Level 14, he says:
  'G... GUESS SHE SHOULD HAVE WORKED MORE ON THE DEFENSES...'
  '...'
  'YOU MAY HAVE DEFEATED ME... BUT...'
  'I KNOW. I CAN TELL FROM THAT STRIKE, DARLING.'
  'YOU WERE HOLDING BACK.'
  'YES, ASGORE WILL FALL EASILY TO YOU...'
  'BUT YOU WON'T HARM HUMANITY, WILL YOU?'
  'YOU AREN'T ABSOLUTELY EVIL.'
  'IF YOU WERE TRYING TO BE, THEN YOU MESSED UP.'
  'AND SO LATE INTO THE SHOW, TOO.'
  'HA... HA. AT LEAST NOW, I CAN REST EASY.'
  'KNOWING ALPHYS AND THE HUMANS WILL LIVE ON...!' and deals more damage At Murder Level 15, the damage dealt is set to a random number from 900,000 to 999,999, whereas at Murder Level 14, the damage is set to a number from 34,000 to 37,289. than when he's killed at Murder Level 14.