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).
The choices the player makes will affect the outcome of the story. There are three different main endings: True Pacificist, Genocide, and Neutral. (There is also a fourth one called Hard Mode.) In the Neutral Route, the player kills some monsters yet spares others; therefore, they do not meet the requirements of either the True Pacifist Route or the Genocide Route.
While there are dozens of different versions when it comes to the ending of the Neutral Route, they all revolve around Sans calling the player and leaving a message on their Cell Phone. The message will differ depending on the choices they made. Also, Asgore always dies, Flowey is always defeated, the six human SOULs are always lost, and all the monsters stay behind because the barrier closes following the player's escape from the Underground.
8 Sparing Toriel's Life
Toriel is a sweet old lady who the player encounters in the Ruins pretty soon into their journey. She saves them from Flowey at the start of the game and then guides them through the Ruins.
In the last part of the Ruins, the player must fight Toriel to prove they are tough enough to survive the Underground. If the player spares her, Toriel will leave the cozy home in the Ruins and go back to her throne to rule over the Underground again. She puts forth a new policy: monsters are not allowed to harm humans that fall into the Underground anymore.
There are three variants of this ending too (following Asgore's demise). If the player befriends Papyrus and Undyne and kills no monsters, Toriel tells everyone not to give up. If the player kills less than 10 monsters or Mettaton, Undyne winds up hating the protagonist since they killed someone. If the player kills more than 10 monsters, Papyrus, or Undyne, a rebellion is formed to overthrow Toriel following backlash since people still died despite her peace policy.
7 Killing Toriel But Sparing Undyne
Undyne is a passionate, fishy monster that the player encounters during the Waterfall level. She follows them and attacks often but the player is saved by their own dexterity or Monster Kid.
At the end of the Waterfall level, the player fights Undyne once and for all. If her life is spared, she becomes the ruler of the Underground. This only happens if Toriel is killed beforehand. Undyne enforces a new policy: kill all humans who enter the Underground. She also militarizes the monsters, vows to destroy the barrier and wage war on the humans, and plans to hunt down and murder the player by her own sword.
6 Killing Toriel And Undyne But Sparing Mettaton
Mettaton is a robot with a SOUL, both literally and figuratively, that the player encounters throughout the Lab. He forces the player to be a guest on his quiz show and his cooking show, as well as perform in his musical.
At the finale in the Lab, the player winds up battling Mettaton. If he is not killed, Mettaton becomes the ruler of the Underground. This will only occur if both Toriel and Undyne die prior. He winds up brainwashing all the monsters in the Underground with his TV show. However, there is an upside: Mettaton also establishes a policy throughout the Underground that allows humans to join his fan club, free of charge.
5 Killing Toriel And Undyne And Mettaton But Sparing Papyrus
Papyrus is the brother of Sans but most importantly the most flamboyant skeleton in the history of video game characters. The player meets him in Snowdin Forest, where he has them go through several puzzles until eventually fighting them at the end of the level.
If the player decides not to kill Papyrus, he naturally becomes the ruler of the Underground (with help from Sans). This will only become reality if Toriel, Undyne, and Mettaton are dead. Papyrus institutes a policy that dictates humans are not entirely bad, nor good, and cannot be judged either way. However, they must always do puzzles. With Papyrus leading the way, the Underground becomes better than ever and he cooks spaghetti for all the monsters.
4 Killing Toriel And Undyne And Mettaton And Papyrus But Sparing All The Other Monsters
If the player kills Toriel, Undyne, Mettaton, and Papyrus, yet spares all the other monsters, then a dog becomes the ultimate ruler of the Underground.
This small, white, happy, annoying dog will simply sleep on the throne and do nothing at all when it comes to leading the Underground. Still, according to Sans at least, this outcome is okay. In fact, all the monsters continue living their lives under the dog's regime and life is...good.
3 Killing Toriel And Undyne And Mettaton And Papyrus And Every Other Monster
If the player kills Toriel, Undyne, Mettaton, Papyrus, and all the other monsters in the Underground, then anarchy is enabled. This ending is still achieved if at least one non-boss monster is killed.
Without any leadership at all, the Underground becomes a depressing place to live. The monsters feel doomed, destined to live in the dark, trapped in the Underground for eternity until they die a sad death. Sans is still around but he refuses to become the ruler because he likes chilling too much.
2 Killing Absolutely Everyone But Then Quitting Cold Turkey
If the player kills all the monsters along the way from the Ruins and throughout the Waterfall level but then suddenly spares everyone during the Hotland level, they will not encounter Alphys. She is a reptilian monster as well as a doctor and a scientist who the player typically meets in the Lab.
In fact, Alphys is elsewhere; she is the new ruler of the Underground. After finding out Undyne was no longer living, Alphys evacuated the remaining monsters to a safe location.
1 Sparing Flowey's Life
Flowey is the first and last character the player encounters. He is basically the main villain, infamous for his mantra: "KILL OR BE KILLED."
If the player spares Flowey's life during the final boss fight of the game, he talks to them. If the player killed some monsters, Flowey suggests restarting and not killing anyone for a "happy ending." If the player killed no monsters at all, Flowey tells them to restart and befriend Papyrus, Undyne, and/or Alphys. If the player kills all the monsters except for Flowey, he tells them to restart because they were so close and that Flowey will be "waiting" for them.