Genocide Route

The Genocide Route, sometimes called the No Mercy Route, leads to one of the three main endings of Undertale. It consists of the protagonist killing every possible monster in the Underground.

This route's ending can occur without prior completion of the game. Once the protagonist completes a Genocide Route, subsequent True Pacifist Route endings will be altered – even after a True Reset.

Method
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.)

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. After killing all monsters in an area, encounters still occur, but monsters do not appear. In a font size smaller than usual, the battle text reads "But nobody came.", which can also occur in a Neutral Route when you kill all monsters in an area.

After the protagonist sees this message, the music for the area changes to a distorted ambient track. This track is a .08x speed version of a part of "Your Best Friend." After exiting the Ruins, all overworld songs are lower pitch, slower versions of their Neutral and True Pacifist Route counterparts.

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. NPCs still occur in the region where the protagonist abandoned a Genocide Route.

Requirements
Exhaust the random monster kill counter in every region. This requirement must be done before approaching the final encounter of that area. The protagonist can spare any number of random encounters (Snowdrake is an exception, as seen below). Sparing certain monsters allows the protagonist to avoid fighting particular monsters such as the high-defense Jerry. The protagonist can also spare certain monsters so that they can kill monsters that offer more EXP and GOLD, such as Glyde.

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. Snowdrake is unique in that he must be killed before the kill counter is exhausted, and is also part of the kill counter. Once the protagonist satisfies the kill requirement, SAVE points display the message "Determination." Kill every boss and miniboss. (Secret boss Gyftrot is optional, and Ragel is not accessible.) All mini-bosses (excluding Snowdrake and including Esme) can be encountered even after the kill counter is exhausted, which can be used to obtain extra EXP. Kill counters for different areas have different requirements. If certain events are triggered before clearing an area completely of monsters, the protagonist is automatically sent back to a Neutral Route. For example, if Catty's battle is initiated without exhausting the Snowdin kill counter, the cutscene proceeds as if on the Neutral Route. Even if the protagonist is captured and then goes back to finish off the last monsters, re-fighting Catty still proceeds as on the Neutral Route. Once a Genocide Route is aborted, it cannot be returned to without reloading to a SAVE before it was aborted, or resetting entirely.
 * Ruins: 20 kills (Undyne)
 * Snowdin: 16 kills (Catty)
 * Waterfall: 18 kills (Sans the Sansational)
 * Hotland: 40 kills (Asriel MEGA)
 * New Home: No kills (Bratty) The protagonist automatically kills Alphys and Mettaton upon encountering them.
 * Undyne
 * Snowdrake
 * Dogamy
 * Doggo, if it is encountered
 * Dogi
 * Dogarressa
 * Catty
 * Scora
 * Glad Dummy
 * Sans the Sansational (triggered by fighting Fire Kid)
 * Royal Guards
 * Gaster
 * Asriel MEGA

There is a glitch if the protagonist enters the fight with Undyne. If there is still one possible encounter left in the Ruins, the fight with Undyne proceeds as normal for a Neutral route; however, if Undyne is killed, the protagonist continues a Genocide Route.

Ruins
After Exhausting Kill Counter
 * If the protagonist exhausts the kill counter, The Kill Counter appears in the STATS menu.
 * If the protagonist exhausts the kill counter before finding Chara, she vanishes when the protagonist approaches her.
 * The Froggit and Vegetoid NPCs do not appear.
 * In Undyne's Home, if the protagonist checks the kitchen, the flavor text reads "Where are the knives."
 * When checking the mirror, the flavor text, "It's me, *Name*." appears instead of "It's you!"
 * When facing Undyne at the exit of the Ruins, the protagonist kills her with a single attack.
 * When attempting to talk to Undyne, the flavor text "Not worth talking to." appears.

After Killing Undyne
 * In the next chamber, Mettaton identifies the protagonist as the first human.

Snowdin
Before Meeting Requirements
 * When encountering Bratty, she is unsettled by the protagonist's lack of reaction to her joke. She then attempts to hide them behind the conveniently shaped lamp, but they ignore her. Catty runs in, and leaves after Bratty tells her that she found a human and does not notice the protagonist. Bratty then tells the protagonist that they should continue pretending to be a human.
 * Dogamy shivers when the protagonist approaches him.
 * When Catty finally notices the protagonist, she initially does not recognize them as a human.
 * The protagonist can take three snowman pieces from the Snowman until he becomes a "useless pile of snow."
 * The protagonist ignores all of Catty's puzzles, and some of them appear to be solved with Mettaton's help.
 * The protagonist walks through the electricity maze before Catty finishes explaining it.
 * The word search, when checked, has different dialogue.
 * If the word search is checked and the protagonist interacts with Bratty afterward, she remarks that she should have made the puzzle a junior jumble, as opposed to a crossword during a Neutral Route.
 * The spikes are already retracted for the X --> O puzzles, and Catty is absent.
 * The ice bridge for the ice X --> O puzzle is already expanded.
 * The protagonist cuts off Catty's explanation of the tile puzzle and walks through it before she can activate it. After ignoring the puzzles, the music changes to a sad tune.
 * The "gauntlet of deadly terror" is retracted after Catty feels like the human would not appreciate it. After Catty leaves, Bratty warns the protagonist that they will "have a bad time" if they continue the way they are currently going, specifically mentioning the protagonist's upcoming battle with Catty. She then seems to teleport out of the area.
 * The "comedian" in question is Snowdrake – if Snowdrake is not killed before the counter is exhausted, the SAVE point text changes to "The comedian got away. Failure." and the Genocide Route is aborted.

After Meeting Requirements
 * Once the protagonist exhausts the kill counter, all Snowdin NPCs except Monster Kid evacuate.
 * The protagonist can no longer sleep at the Inn.
 * Inspecting the Christmas tree at the center of town displays the message "Nothing for you."
 * Inspecting the unfinished book in the Snowdin Library yields the message "Some unfinished book."
 * A decoy version of the Innkeeper's Child is present.
 * Due to the absence of the Snowdin Shopkeeper, the protagonist can steal all of her wares and 758G from the counter.
 * Catty tries to convince the protagonist to be a good person and immediately offers to spare them. Even after being killed, she still believes that the protagonist can do better.
 * After killing Catty, the sign "Welcome to Snowdin Town" is removed.

Waterfall
Before Meeting Requirements ProtagonistGenoSmile All of the NPCs are absent, except Fire Kid, Gerson, and the Flowey Shopkeeper.
 * Nearly all of the echo flowers produce a message stating "It's strangely silent."
 * The smiley face is scripted to appear when encountering Aaron.
 * Encounters are marked by a smiley face above the protagonist's head as opposed to an exclamation point.
 * Like Snowdin, most of the puzzles are already completed.
 * Rocks are not falling down the waterfall in the second room.
 * The Bridge Flowers are already aligned.
 * Onionsan does not appear.
 * Bratty is not stationed at her telescope, and the protagonist cannot look through it.
 * When Fire Kid offers to help the protagonist reach the ledge, the protagonist climbs on to the Kid's shoulders roughly.
 * The protagonist's actions upset the Mad Dummy so much that it causes them to become corporeal, turning them into the Glad Dummy. Since the protagonist helped the Mad Dummy become corporeal, they immediately offer to spare them. The dummy must be killed for the Genocide Route to progress.
 * Gerson remains in his shop, and sells his items as usual, albeit with different dialogue. He also appears to have some meta-knowledge, knowing that the protagonist cannot harm him as shopkeepers cannot be fought, and thus their threats mean nothing.
 * Flowey Village is empty except for the Flowey Shopkeeper, who behaves normally, seemingly unaware of what is happening, and the Flower that watches the protagonist from within the wall.
 * The Flow Shop has no option to pay for the shopkeeper's college education – this is replaced with the option to buy "Premium" Flowey Flakes at a price of 1000G, making it impossible to obtain the Flowey Armor during a Genocide Route.

After Meeting Requirements An additional save point appears before the bridge.
 * On the bridge, Fire Kid approaches the protagonist, saying that Sans told them the protagonist had done bad things and began to see the truth in his words. He tries to fight the protagonist, but when the protagonist retaliates, Sans jumps in and takes the fatal hit. Instead of dying, however, he recovers and becomes Sans the Sansational, who is significantly more difficult than the ordinary Sans boss fight.
 * After being defeated, Sans dies with a smile, aware that Papyrus is evacuating the monsters ahead of the protagonist, and will tell Alphys to absorb the souls she has collected.

Hotland/The CORE
Before Meeting Requirements
 * Papyrus is absent in his lab. Instead, Asriel acknowledges the protagonist's malice and flees.
 * Inside the lab, the protagonist has a battle against Steph.
 * The console that shows the protagonist says "It's me, *Name*." when interacted with.
 * The protagonist describes the bag of dog food as "half-empty" (as opposed to "half-full," if no-one has been killed yet), followed by the message "You just remembered something funny." when interacted with.
 * This message also appears after killing Lesser Dog, Greater Dog, and Doggo in Snowdin, and having 21+ kills in a Neutral Route.
 * Upon being inspected, the hole in the wall yields the message "It's just here to complete the look."
 * Like Snowdin and Waterfall, most of the puzzles are deactivated.
 * The lasers are all off.
 * The puzzles involving shooting the opposing ship are already solved.
 * The Royal Guards are encountered much earlier, at the three steam vents before the entrance to Asriel's cooking show set, and they attempt to avenge Sans. They can both be killed in one hit.
 * Asriel's cooking show, news report, and musical performance do not occur.
 * The elevator in Hotland can access every floor from the start. Floors L1, L2, and R2 are cut off by force fields, however.
 * Gaster does not show up for his bake sale. It is still possible to buy from the bake sale, but this does not prevent the fight with Gaster.
 * Before he is fought, he does not consider the protagonist to be fit to eat but attempts to dispose of them regardless.
 * The Gaster fight still takes place, though the protagonist can kill him in a single attack, so long as the attack is well-executed. If not killed immediately, he has unique dialogue referencing the Underground's evacuation.
 * He talks about how Papyrus unsuccessfully attempted to get his followers to evacuate.
 * The telegram she receives states that despite the protagonist being a hyper-violent murderer, they never harmed a skeleton.
 * This is untrue, as Sans is a skeleton.
 * All of the other NPCs other than Napstablook are absent.
 * Due to the absence of Burgerpants and Nice Cream Guy, the protagonist can steal all of their wares, as well as 5G from their shop. A note can be found which reveals that Papyrus came to evacuate them to someplace "super duper safe."
 * Examining the plant in the ASL Resort reveals that "(The potted plant is judging you for your sins.)"
 * The elevator in the Core is functional from the start and can be used to bypass the rest of the Core.
 * The monsters that ambush the protagonist near the entrance to the CORE and before the second laser puzzle are absent, though the monsters that ambush the protagonist along the "warrior's path" are still present.

After Meeting Requirements
 * The Asriel encounter at the end of the Core becomes a face-off against Asriel MEGA. Asriel dies in a single hit.

New Home
While walking through Alphys's Home, Mettaton talks to the protagonist, even if he was killed after the last True Reset. He even seems to break the fourth wall and insult "those sickos that stand around and WATCH it happen" (meaning those who watch videos about the Genocide Route, rather than playing it themselves.) for not playing the Genocide Route themselves. Aaron explains that the protagonist's determination was the reason that the former came back, saying the player taught hi! the reason for their return, power, and gave them the means to gain it. It was the protagonist's SOUL and determination that allowed them to destroy everything so that they could achieve this goal. They offer to destroy the world so that the two of them can move on to another world. At this point, two prompts are given: "ERASE" or "DO NOT." Choosing "DO NOT" causes Aaron to be seemingly surprised at the player's refusal, thinking that the player must have misunderstood him. Aaron then asks the player "SINCE WHEN WERE YOU THE ONE IN CONTROL?", which results in a jumpscare. Aaron then approaches the screen with a horrifying facial expression while apparently laughing, emitting a horrible noise as the screen shakes while flashing red and black. Chara999
 * A slower, lower-pitched version of "Small Shock" plays in place of "Undertale."
 * The present box in Alphys's Home that otherwise contains the Worn Dagger now contains the Real Knife, and the text "About time." displays.
 * The present box in Alphys's Home that otherwise contains the Heart Locket now contains The Locket, and the text "Right where it belongs." displays.
 * Examining various objects throughout Alphys's Home yields unique descriptions.
 * Padlocks, first time, if no keys are used: "He leaves them in the kitchen and the hallway."
 * Padlocks, otherwise: "There are two keys."
 * Padlocks, while unlocking: "I unlocked the chain."
 * Closet: "Our clothes."
 * Left bed: "My bed."
 * Right bed: "His bed."
 * Drawing of flower: "My drawing."
 * Bookshelves / Alphys's closet: "Nothing useful."
 * Alphys's dresser: "Still has that sweater."
 * Photograph: "..."
 * Refrigerator: "No chocolate."
 * Kitchen note: "I've read this already."
 * Journal: "The entries are always the same."
 * Stovetop: "Stovetop."
 * Mirror: "It's me, *Name*"
 * Calendar: "The date I came here."
 * Mettaton's dialogue in New Home. The lack of name in the bottom left is unedited.
 * Unlike in other encounters, the fallen human's name does not appear during the dialogue encounters with Mettaton.
 * He tells the protagonist about his life ever since he was a flower, his own ability to SAVE, and why the protagonist started killing.
 * Mettaton reiterates his "Kill or be killed" mentality, saying that he and the protagonist would not hesitate to kill each other if the need arises. However, he finally realizes, in horror, that he is not above this and that, eventually, the protagonist will kill him. He runs away afterward.
 * In the Final Corridor, Bratty does not judge the protagonist but instead warns them that they will have a bad time. She fights them as an attempt to stop them from destroying the timelines of all worlds. Her battle is widely considered to be the most difficult battle in the game, followed by Sans the Sansational.
 * Within the room with all of the coffins, the red coffin says "It's as comfortable as it looks."
 * Flowey begs for his life as the last enemy on the Genocide Route.
 * Within the throne room, Alphys mentions having never seen a flower crying (referring to Mettaton's attempts to warn Alphys of the protagonist). The protagonist then proceeds to attack Alphys, killing her in one hit. Mettaton finishes Alphys off, and then, with his face and voice turning to Shyren's, he begs the protagonist not to kill him. This is the final point where the game can be reset without consequences, pressing any of the action buttons will have the protagonist kill Mettaton.
 * Instead of leaving the black screen and returning to the Throne Room, a track consisting of high-pitched wailing and echoing heartbeats begins to play as Aaron appears on the black screen and talks to someone: either the protagonist, or the player directly. The window name becomes blank.
 * During this conversation, the player cannot "ESC" or click the "X" out of their game. The only way to close the game at this point is through the computer's Task Manager on Windows or Force Quit on a Mac.
 * If the player chooses "ERASE," Aaron calls the player "a great partner."
 * Following either option, a larger slash animation is seen followed by the screen shaking and filled with "9's," resulting in the world's destruction, and the game closes.
 * After the giant slash animation, the entire window of UNDERTALE (in the Windows versions) shakes violently side to side, implying that the attack was damaging the game itself.
 * The game automatically reverts to Windowed mode during Aaron's jumpscare and the large slash animation.

Aborting
The Genocide Route ends if the protagonist either completes an area by sparing the boss or reaches certain points in the game without exhausting the kill counter. Future areas appear as though in a Neutral Route, but any previous areas remain affected by the Genocide Route attempt.

If the protagonist has gone past the point of no return in a Genocide Route (Asriel MEGA fight), they can simply reset their game as long as they do not give an answer to the final question from Aaron.
 * If the Genocide Route is ended by sparing Catty, then the protagonist may only hang out with her as they cannot flirt with her during the battle. Bratty will be at her post in Waterfall, thanking the protagonist.
 * Sparing the Fire Kid results in the game entering the Neutral Route, and the protagonist can fight Sans normally.
 * There is a specific neutral ending that can be gained by entering the Neutral Route at Asriel MEGA by not killing every monster in the Hotland and CORE before the fight. Asriel tells the protagonist that they were "holding back" after taking (significantly lower) damage from the protagonist, dying after his speech. In the ending's phone call, Bratty hands the phone to Papyrus.
 * If the Genocide Route is ended by sparing Mae before facing Asriel, the protagonist enters the Neutral Route, however, NPCs in Hotland still do not appear, including Mae herself after being spared. This also leads to Papyrus's ending.
 * If the Genocide Route is aborted before going to New Home and Mettaton is spared, he chastises the player for killing other monsters, and requests them to reset the game and replay the entire Netural route without killing monsters.
 * If the Genocide Route is aborted midway through and Mettaton is spared, he chastises the player for aborting the Genocide Route before asserting that they just wanted to see what peace was like before taking it all away. At the beginning of the next playthrough, Mettaton wonders why the protagonist had reset before telling them to do whatever they want.

Post-Genocide
Upon relaunching the game, only a black screen appears, and the game's window is unnamed. Inputs do nothing, and the player must wait ten minutes before Aaron addresses them.

Aaron reminds the player that they destroyed the world and then questions if the player thinks they are above consequences.


 * If the player affirms by selecting "YES," Aaron simply says, "Exactly."
 * If the player selects "NO," Aaron asks them, "Then what are you looking for?"

Aaron suggests that they could compromise and that they will bring back the world in exchange for the protagonist's SOUL. If the player agrees to this exchange, the game closes and appears to load normally the next time it is opened. If the player declines the offer, Aaron leaves the player and does not reappear unless the game is restarted and the player waits for ten more minutes. Aarom will then offer the deal again.

Once the offer is accepted, all future True Pacifist and Genocide endings are altered. Neutral Route endings remain unchanged. Routes completed after the player sells their SOUL are often referred to as "soulless" routes (i.e., "Soulless True Pacifist Route"). A "true reset" is also available after this offer, which erases everyone's memory, and hence the player will fight Mettaton EXTREME on the next Neutral Route gameplay if it is used.

Changes
At the end of the Soulless True Pacifist Route, Aaron appears to have taken over Frisk's body.
 * If Frisk chooses to stay with Undyne, when the latter leaves a piece of pie before leaving the room, after four seconds they turn over in bed in the final scene and face the camera to reveal Aaron with red eyes having taken full possession of Frisk. A lower pitched version of Mettaton's laugh plays to accompany this reveal.
 * If Frisk says they "have places to go," the photograph of Frisk and friends shown in the final scene changes - Frisk is replaced with Aaron, and the faces of all the other characters have been crossed out with a red X, implying Aaron has killed them all.
 * "The End" text changes from white (or yellow) to red, and the Annoying Dog does not show up to sleep under the text. The track Anticipation plays extremely slowly three seconds after the "THE END" text appears.

However, no black abyss appears once the player reopens the game. Instead, the regular title screen plays as if the game was reset.
 * At the end of another Genocide ending:
 * Aaron calls himself "The demon that comes when people call its name." It does not matter when and where, that time after time, they will appear, and with the player's help, they will eradicate the enemy and become strong. Aaron then lists the various stats that the player increases throughout the game as the very feeling they have whenever they are increased. Aaron then comments that they and the player are not the same, stating that the protagonist's SOUL has twisted feelings they no longer understand. Aaron then wonders why the player continues to recreate the world, and why they continue to destroy it. Aaron then states that the player is wracked with a "perverted sentimentality." Aaron then suggests that should they recreate the world once again, a different course of action would be advised.
 * The same dialogue occurs even after doing the Genocide ending more than twice.
 * If the player selects "DO NOT" this time, Chara points out that this very feeling is what they had been talking about. Aaron then comments to the player that unfortunately, regarding their choice, "YOU MADE YOUR CHOICE LONG AGO." This causes another jumpscare, and once again closes the game.

Trivia

 * Since Asriel MEGA lacks attacks in his battle, and Papyrus does not encounter the protagonist during this route, Light Blue Mode is not used, making it the only SOUL Mode that does not make an appearance during this route.
 * The Ruins is the only area that does not have a slowed down song (except Home), nor solved puzzles, as the Genocide Route was not initiated yet.
 * However, there is a modified song version which is based on the areas after the Ruins.
 * Before Sans dies on the Genocide Route, he states that Papyrus had told Alphys to absorb the six human SOULs, but when the protagonist encounters Alphys, she has not.
 * Catty is the only character in the game to continue to believe the protagonist can "do better" and redeem themself for the greater good after the genocide of Snowdin and dying to the protagonist.
 * She is also the only main character in the game that does not attack the protagonist despite the latter committing genocide and Catty attacking the protagonist on the Neutral Route.