Undertale is an indie 2D RPG video game released on PC in September 2015, on PS4 (and PS Vita) in August 2017, on the Nintendo Switch in September 2018, and on Xbox One (and Xbox Series X/S) on March 16, 2021. Developed by Toby Fox, the game follows a child who has fallen into the Underground on his journey back to the surface. The player has the choice of whether or not to kill all the monsters they meet (or just some) or spare all of them (or just some).

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The choices the player makes will affect the outcome of the story. There are three different main endings: Neutral, True Pacificist, and Genocide. (There is also a fourth one called Hard Mode.) In the Genocide Route, the player kills every single monster in every single area in the game.

The Genocide Route is the only way for players to fight Sans (in addition to Asgore and Flowey) and listen to the infamous "Megalovania" track during the game. While the player must complete the Neutral Route before the True Pacific Route, the Genocide Route has no prerequisite. However, after they finish the Genocide Route, the game is forever altered (regarding a subsequent True Pacifist Route), even after a True Reset.

8 Everyone And Everything Must Die

Undertale But Nobody Came

How does the player know they have killed all the monsters? Because encounters will no longer occur (before the final encounter) in the level. After they trigger enough random encounters and slay monster after monster, battles will read: "But nobody came." And, the music in the overworld is at a lower pitch and slower tempo. Also, there are signs throughout the game that only appear if the player is on the right (genocidal) path.

In addition to the monsters, all the bosses and minibosses must be destroyed too: Toriel, Snowdrake Doggo, Lesser Dog, Dogi, Greater Dog, Papyrus, Shyren, Glad Dummy, Undyne the Undying, Royal Guards, Muffet, and Mettaton NEO.

7 The Murderer In The Ruins

Undertale Where Are The Knives

If the player drains the kill counter in the Ruins (20 kills) before running into Napstablook, they will vanish before the player can fight them. Also, Froggit and Vegetoid will not appear (their NPCs).

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In Toriel's Home, the cupboard in the kitchen will say: "Where are the knives." And, the mirror will say: "It's me..." followed by the player's name instead of "It's you!" After killing Toriel, there is flavor text that reads she is "Not worth talking to."

6 The Slayer In Snowdin

Undertale Snowdin Save

After exiting the Ruins, the save points do not say the player is "filled with determination" anymore. They now give a counter to how many more kills they need to complete the Genocide Route portion of the current area.

If the player exhausts the kill counter in Snowdin (16 kills), all of the NPCs will get the heck out of there except for Monster Kid. Also, the player can no longer stay at the Inn and there is a decoy standing where the Innkeeper's Child once stood. The Christmas tree in the center of town says: "Nothing for you." Additionally, the player can steal everything from the Snowdin Shopkeeper since she is gone.

(The player must be aware that they must kill Snowdrake and Lesser Dog before satisfying the kill counter. Both of them are part of it too.)

5 The Assassin In The Waterfall

Undertale Monster Kid

From the Waterfall area onwards, encounters trigger a smiley face above the player's head instead of an exclamation point. While most NPCs are gone (because they are terrified), Monster Kid, Gerson, and Temmie Shopkeeper stick around.

If the player depletes the kill counter in the Waterfall area (18 kills), the "Welcome to Snowdin Town" goes away. Additionally, an additional save point will appear before they reach the bridge. Then, Monster Kid will try fighting the player. However, Undyne saves them and then transforms into Undyne the Undying before not dying.

4 The Hunter In Hotland (And Killer In The CORE)

Undertale Mettaton NEO

At the Lab in Hotland, Alphys is nowhere to be found. (Mettaton is there, but flees.) Muffet still appears and still holds her bake sale. But the rest of the NPCs (except Burgerpants) are gone. The player can steal everything from Bratty and Catty since they evacuated.

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If the player depletes the kill counter in both Hotland and the CORE (40 kills), Mettaton will be upgraded into Mettaton NEO. After his defeat, the player is automatically set to 19 LOVE and no more encounters trigger going forward.

3 The Butcher In New Home

Undertale Asgore Home

There are no kills required in New Home, the final area of the Genocide Route.

The present box in Asgore's Home now has a Real Knife and The Locket, instead of the Worn Dagger and the Heart Locket. When equipped, the flavor texts are "About time" and "Right where it belongs," respectively. Also, numerous objects in the house have unique descriptions.

Rather than learning about Asriel, the player talks to Flowey in Asgore's Home and learns about his story instead. However, even he is scared of the player at this point in the game.

2 The Executioner In The Throne Room

Undertale Sans Fight

Before entering the Throne Room, the player fights San in the Last Corridor (right after he says "You feel like you're going to have a bad time"). They instantly reach 20 LOVE after killing Sans, although the fight is nothing to sneeze at.

In the Throne Room, the player will face Asgore yet end him in just one hit. It is Flowey who is the real threat, appearing to finish off Asgore and then beg the player for mercy. At this point, the player gets one final chance to reset the game without consequences. If they proceed, Flowey dies...and Chara appears.

1 Welcome To The End Of The World

Undertale Chara

Following the point of no return, the player will see a black screen and hear the wind howling upon botting up the game going forward. They must wait 10 minutes before Chara appears, reminding them they already ended the world.

If the player thinks they are above consequences, nothing happens. But if not, Chara will bring back the world they destroyed in exchange for their SOUL. The game will reset and reload as normal but in reality, nothing will ever be the same again. (The subsequent True Pacifist and Genocide Routes are altered.)

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