History NightmareFuel / Undertale

* There's something deeply disturbing about the cutscene after defeating Sans. [[WildMassGuessing What appears to be]] ''blood'' comes out of him, something no other monster is ever shown with due to monsters being explicitly stated to be made of dust. On top of that, besides [[IWarnedYou a brief-yet-ominous warning of what's to come]], he seems utterly detached from reality in his final moments; instead of commenting on his death or you being well over the MoralEventHorizon at this point, [[FamousLastWords he just casually says he's going to Grillby's]], even though the place -- along with most of the underground -- is empty at this point. And then he asks his brother if he wants to come along for food, even though you killed Papyrus some hours ago.

** Also, as Flowey begins growing terrified of the Fallen, the somewhat sad, ambient music is replaced with the slowed-down version of 'Anticipation' mentioned above. It fits the moment of him realizing that even ''he'' isn't safe from being killed and slowly growing scared perfectly.

* Any phrase that comes from the Fallen Child can be quite disturbing. Especially when they talk in entirely red sentences like the "where are the knives" example above. Notably, SAVE points change to them telling you how many monsters are left to kill in each area. After the work is done, what would be a fluffy comment about feeling inspired by something in the room becomes a blunt "Determination".

* During the walk through Asgore's home, Flowey talks to the Fallen Child in place of the usual monsters, and talks about how they're the only one who understands them even after all the time that's passed since he knew them as Asriel. However, after pointing out how guys like them wouldn't hesitate to kill each other if they got in each other's way, Flowey comes to a horrifying realization: ''he'' can be a target for you. He begins shaking in fear and starts pleading with them to back out of the plan despite being on board with it for most of the run. That's right — you're so twisted that even ''Flowey'' is terrified of you despite being his only 'friend.'

*** One of the Memoryheads will sometimes say "Lorem ipsum docet." While on the surface is seems like a random reference to the [[http://en.wikipedia.org/wiki/Lorem_ipsum lorem ipsum placeholder text]], the full phrase could be roughly translated as "Pain teaches."

* The official [[https://www.youtube.com/watch?v=srZdDAJbHfc 5th Anniversary Concert]] is a SugarWiki/CrowningMomentOfAwesome through and through, but the prelude to the Genocide Mode music is ''terrifying''. After playing the upbeat Pacifist Mode credits music, the orchestra plays the game's cheery menu theme, but in the middle of it the music [[MoodWhiplash suddenly turns]] ominous and discordant. The live chat replay even shows viewers wondering if it's over, only to react with shock and horror when the music takes a turn for the dark. As if to symbolize Frisk/Chara's path of bloodshed up to Undyne, the orchestra also plays dreary DarkReprise's of Heartache and Bonetrousle, presumably symbolizing the deaths of Toriel and Papyrus. And after playing Megalovania, the concert doesn't immediately wrap up; the stage turns dark and most musicians leave their seats as a droning static plays, presumably symbolizing the state of the universe after Chara destroys it. Only a few remaining musicians playing a mild reprise of the Menu theme (and Toby's piano playing [[TheStinger after the credits]]) saves the concert from ending on a very dark note.

** The simple fact that Flowey is ''[[RidiculouslyCuteCritter Asriel]]'' adds more eeriness to his character. As we're shown in the Pacifist Route of the game, Asriel is nothing more but a sweet, well spoken, if very shy monster who was dragged into a situation beyond his control by the Fallen. Learning that he went from that to [[StrawNihilist a violent monster]] all in a desperate attempt to reunite with the Fallen/Chara makes it more horrifying and saddening, especially when you remember that, as stated above, Asriel is ''eight years old''. All of that trauma arguably [[DrivenToMadness took a toll on him]], making him [[MaddenIntoMisanthropy see the Underground as simple pieces that became repetitive]], and [[StartOfDarkness involving the simple mantra he stuck by]] until Frisk showed up: Killed or Be Killed.

* It's hard to die to Toriel, as when your health drops too low, she'll start to actively avoid attacking your SOUL. But if you do die, you'll witness an [[http://imgur.com/WWC20wC blink-and-you'll-miss-it expression]] of ''absolute horror'' on her face, right as [[MyGodWhatHaveIDone she realizes that — a moment too late — she's accidentally killed you]]. You don't know what happens next, since you don't see what happens [[TheNothingAfterDeath when everything goes to black]], but it isn't much of a stretch of the imagination that she would be literally [[DeathWail screaming her head off]].

* The [[SurpriseCreepy dancing mushroom guy in Temmie Village]] is a minor example.
** Similarly, there's an NPC in Grillby's bar whose face is nothing but a giant fanged mouth. They're friendly, like most monsters in the game, but they may make a few players jump when first seeing them.

* The Neutral endings are bittersweet at best and heartbreaking at worst. If Undyne doesn't work with Alphys or if she doesn't rescue remaining monsters from the walking apocalypse you are, it is heavily implied [[DrivenToSuicide she committed suicide in the True Lab]], three of them take the cake:

** Some of the [=NPCs=] themselves are pretty creepy. One looks like a grey Monster Kid, but with no pupils. Another is a talking head (possibly Gaster's head itself) being held by a weird humanoid (actually a recoloring of an existent NPC, but with fewer features). The worst of them all, however, is probably Follower 3, which looks like a giant, bizarre, disembodied head that's sticking out from the ground (although the appearance of its normal, recolored counterpart in ''VideoGame/{{Deltarune}}'' reveals that it's actually just a weirdly-shaped [[BirdPeople humanoid bird]]).

->"Welcome to my special hell."

-->--'''Lemon Bread'''

* The towns are [[GhostTown completely empty]] on the No Mercy route, with notes from shopkeepers expressing fear over their life. The few people that the protagonist ''can'' talk to are either completely hostile (and rightfully so) or blissfully ignorant (such as Monster Kid, who the protagonist later attempts to murder, with the Check text saying "Looks like free EXP").

* If you check the coffins, Chara says (in red text), "It's as comfortable as it looks." ''[[BackFromTheDead Brr]]''...

---> "WARNING! WARNING! ELEVATOR LOSING POWER! EM TETHER STABILITY LOST! ALTITUDE DROPPING!" ''(screen [[FadeToWhite fades to white]]) '''(CRASH!)'''''

---->"Long ago, two races ruled over the Earth: HUMANS and MONSTERS. One day, '''they all disappeared without a trace.'''"

--->[[YourApprovalFillsMeWithShame "'''I knew you had it in you!'''"]]<

("It's empty")

** When threatening you, Sans' pupils usually vanish. This actually manages to make him go from looking goofy to just plain scary thanks to BlackEyesOfEvil.

---> '''Sans:''' heh. well, that's your viewpoint. i won't judge you for it. ... '''[[YouBastard YOU DIRTY BROTHER KILLER.]]'''

---> '''Gaster:''' ENTRY NUMBER SEVENTEEN\\

[[WhamLine WHAT DO YOU TWO THINK?]]

--->"But please don't despair! Because the time that you will meet her...\\

* While checking out Toriel's kitchen, you may come across a cupboard full of gingerbread cookie cutters; but if you're particularly ruthless, this description is replaced with a startlingly red "Where are the knives." The fact that no other descriptions are changed makes this even creepier.

--> "Hahaha... You're not really human, are you? No. You're empty inside. Just like me."

-->'''Sans:''' Well, I'll be straight-forward with you. My brother'd really like to see a human... so y'know, it'd really help me out... [[AmbiguouslyHuman if you kept pretending to be one]].

--> '''Sans:''' it's a beautiful day outside. birds are singing. flowers are blooming. on days like these, kids like you...

--> '''Sans:''' so... guess that's it, huh? just... don't say I didn't warn you. (''stands up'') welp. i'm going to grillby's. (''[[TheDyingWalk slowly shambles off the screen]]'') papyrus... you want anything? (''dies offscreen'')

-->'''Asgore:''' Now, now, there's no need to fight. Why not settle this...[[SpotOfTea over a nice cup of tea?]] [''slash, as he collapses to his knees and his eyes erupt with pain''] Why...you... [''Flowey's unavoidable pellet attack surrounds him as he looks on in terror, before it kills him'']

--> '''Entry Number 15:''' Seems like this research was a dead end... But at least we got a happy ending out of it...? I sent the souls and the vessels back to Asgore. And [[TemptingFate I called all the families and told them everyone's alive. I'll send everyone back tomorrow.]] :)
--> '''[[YankTheDogsChain Entry Number 16]]:''' [[RapidFireNo no No NO NO NO NO NO]]

---> monsters' physical forms can't handle "determination" like humans' can. with too much determination, [[BodyHorror our bodies begin to break down]]. [[EldritchAbomination everyone's melted together...]]

-->''No head is connected\\
No body is connected\\
No arms are connected\\
No legs are connected\\

No ears are connected\\

----> "Long ago, two races ruled over the Earth: HUMANS and MONSTERS. One day, '''they all disappeared without a trace.'''"

----> Buuum buuum buuum buuum, buum buuum buuuum - [[HellIsThatNoise d-d-d-d-d-d-d-d-d-d-d-d-d-d-d-d-d-d-d-d-d-d-d-d-d-d-d-d-d-d-d-d-]]

--> [[TranquilFury "I really should have killed you when I had the chance."]]

* If you backtrack a bit after certain points, you can catch Flowey quickly retreating underground. He's been stalking you the whole game. And following you all the way up to the end of the game. On a run where you spare Toriel, find him in the last Waterfall Echo Flower field then talk to the Echo Flower he was just next to. You hear what sounds like Toriel looking for you...but in reality, it's Flowey imitating her voice, then taunting you about how she'll just forget about you the moment she finds another human child. Finding out who Flowey really is adds another layer to this. It's Asriel projecting his own fears and bitterness at the loss of his parents to mock you. If you decide to kill Toriel instead, then Flowey will instead imitate Toriel sounding horrified, wondering where she is, followed by him saying "Hee hee hee... [[ArcWords But nobody came.]]"

--> "It's me, ''[[HelloInsertNameHere (name)]]''."

** Even if you don't pursue the No Mercy ending and incur Sans' wrath, the one time he lets his facade down around you is creepy as hell. If it wasn't for his promise, you'd be dead where you stand. He's not kidding, as you ''will'' learn in No Mercy. Doesn't help that his VoiceGrunting [[NothingIsScarier disappears for that moment]].

* During the walk through Asgore's home, Flowey talks to the Fallen Child in place of the usual monsters, and talks about how they're the only one who understands them even after all the time that's passed since he knew them as Asriel — however, after pointing out how guys like them wouldn't hesitate to kill each other if they got in each other's way, he begins shaking in fear and starts pleading with them to back out of the plan despite being on board with it for most of the run. That's right — you're so twisted that even ''Flowey'' is terrified of you despite being his only 'friend.'

-->-- '''Lemon Bread'''

--> That was fun. Let's finish the job.

--> No one will use this anymore...

-->'''Flowey:''' Clever. Verrrryyy clever. You think you're really smart, don't you. In this world, it's kill or be killed. So you were able to play by your own rules. You spared the life of a single person. Froggit, Whimsun. Vegetoid, Loox. Migosp, Moldsmal. Think about those names. Do you think any of those monsters have families? Do you think any of them have friends? Each one of them could have been someone else's Toriel. [[YouBastard Selfish brat]]. [[WhatTheHellPlayer Someone is dead because of you]].

** The "king Mettaton" ending is CrapsaccharineWorld at its worst: Mettaton is an incompetent and narcissistic ruler who abuses his status to brainwash people and wastes public money to glitter gold everywhere and build monuments to his own glory. If Papyrus is still alive, he mentions things don't go well for those who don't worship the new king. [[FridgeHorror What happens to them exactly?]]
** The creepiest may be the ruler less ending: you practically killed every monster but did not commit Genocide, [[NothingIsScarier you only hear a blowing wind]] behind Sans' voice, and his dialogue implying the Underground has fallen into despair.

** The "aborted Genocide ending, where Alphys is forced to take command after you kill nearly everybody: everyone is worried for their lives and [[TheApocalypseBringsTheBestInPeople Alphys makes her best to calm the situation]]. However, during the call, she cracks a bit. It is disturbing to hear her of all people threaten you so coldly.

** The Mettaton ending is CrapsaccharineWorld at its worst: Mettaton is an incompetent and narcissistic ruler who abuses his status to brainwash people and wastes public money to glitter gold everywhere and build monuments to his own glory. If Papyrus is still alive, he mentions things don't go well for those who don't worship the new king. [[FridgeHorror What happens to them exactly?]].
** The creepiest may be the ruler less ending, [[NothingIsScarier when you only hear a blowing wind]] behind Sans' voice, and his dialogue implying the Underground has fallen into despair.

* EXP and LOVE. In the judgement hall, Sans reveals what these acronyms stand for. '''Ex'''ecution '''P'''oints are a method of quantifying the pain inflicted on others, while '''L'''evel '''o'''f '''V'''iolenc'''e''' is someone's capacity to hurt others and how easy it is for them to distance themselves so they will hurt less. In the underground, they have actual mathematical methods of ''measuring how much pain someone can deal out and how much of a sadist or sociopath they are.'' It makes sense seeing as how monsters are physically affected by things like [[KillingIntent murderous intent]], but it does make one wonder how they discovered these things and evaluated them enough to put numbers and a ranking system on them. What exactly does one execution point represent as a unit of measurement, anyway?
** Well, they did fight a war that pushed them to the edge of extinction. Then again, that's a whole different kind of Nightmare Fuel. Seriously, in this universe, the average human kid could wipe out a horde of monsters by themselves. Trained soldiers probably hit LV 20 in a matter of a couple battles if they didn't go down by DeathByAThousandCuts.

*** This is also how the music is ordered in the official OST, with the prelude to Undyne’s Genocide battle theme coming immediately after the Pacifist Special Thanks music. The exception is the final track Good Night, which doesn’t play in game.

** If you have a fun value of 66, a hallway will appear in Waterfall between the room with Sans’ telescope and the room with the cheese. There’s also a 1/10 chance for a gray door to appear in the hallway, which leads to another room, making the chance of getting it 1/1000. It can also be accessed by changing the fun value in the game's code. The room in question is completely silent and contains only a smiling, deformed skeleton entity with a striking resemblance to [[VideoGame/YumeNikki Uboa]]. Interacting with it will cause it to startle and fade away in thin air. This freaky entity is speculated to be the aforementioned W.D. Gaster, or at least what remains of him.

** There's also a hidden room that can only be accessed by changing a specific value in the game's code. The room in question is completely silent and contains only a smiling, deformed skeleton entity with a striking resemblance to [[VideoGame/YumeNikki Uboa]]. Interacting with it will cause it to startle and fade away in thin air. This freaky entity is speculated to be the aforementioned W.D. Gaster, or at least what remains of him.

* Of all things, [[BewareTheSillyOnes Temmie]] is a potential source of nightmare fuel. You can sell things to their shopkeeper, some of which the shopkeeper says that she really wants. If you then repeatedly refuse to sell the her to them, Temmie says "You will regret this." without any of her usual speaking noises or silly capitalisations and misspellings.

* Of all things, [[BewareTheSillyOnes Temmie]] is a potential source of nightmare fuel. You can sell things to their shopkeeper, some of which the shopkeeper says that they really want. If you then repeatedly refuse to sell the item to them, Temmie says "You will regret this." without any of their usual speaking noises or silly capitalisations and misspellings.

** Once you return to the game, there will still be nothing left. After a while, the Fallen Child offers to bring everything back in exchange for your SOUL. The only thing you can do other than deleting your save files is to accept, which permanently taints your next playthroughs. What was once a heartwarming Pacifist ending turns into the worst possible outcome, as either the Fallen is shown possessing Frisk (accompanied with red eyes and a more terrifying version of Flowey's laugh) after Toriel brings them pie while they’re sleeping or gives you a picture of themselves alongside the other characters... who have their faces crossed off.