History NightmareFuel / UndertaleYellow

** Another version of the hidden Snowdin room will instead have a unicorn-like monster named Wanda . She claims to have ran into the woods to spite her (possibly imaginary) boyfriend, and will spout off a whole lot of other ManicPixieDreamGirl things that seem to reflect very poorly on her mental state, and it's unclear whether she was like this before she ran away or whether the [[EldritchLocation forest]] is ''actively making her go insane''. Like with Jane, the only option the player has is to leave her and be unable to return, so you probably condemned a mentally unwell monster to be lost forever.

*** The third entry, titled "The Phantom SOUL", however, is outright nightmare-inducing, as it goes into detail describing what happens to any human child that falls into the Underground, simply stating that they are "collected". But the real horror comes later, when it goes on to tell the story of a human child that was suddenly spotted in Snowdin, only for them to flee to Waterfall, and this being the last time they were seen... before their SOUL was mysteriously found in the deeper parts of Waterfall. This entry is so disturbing to Clover, they immediately put the book back, and if they later do a Pacifist Route, and make their way around Ceroba's mansion...

*** The music is also worth mentioning. specimen: patchworked sounds [[SoundtrackDissonance joyous and happy, unfitting for the situation]], specimen: organic has the sound of a heart rate machine (which seemingly flatlines at the end) accompanied by a horrid whirring noise that alternates between left and right speakers, specimen: paper sounds like something reminiscent of the [[Videogame/SonicCD Sonic CD US boss theme]], specimen: polygonal sounds like CreepyCircusMusic, and last but not least, specimen: mechanical sounds good at the start, until halfway in, where the electric guitars sound like '''[[HellIsThatNoise ungodly screaming.]]'''

*** The music is also worth mentioning. specimen: patchworked sounds [[SoundtrackDissonance joyous and happy, unfitting for the situation]], specimen: organic has the sound of a heart rate machine (which seemingly flatlines at the end) accompanied by a horrid whirring noise that alternates between left and right speakers, specimen: paper sounds like something reminiscent of the [[Videogame/SonicCD Sonic CD US boss theme]], specimen: polygonal sounds like CreepyCircusMusic, and last but not least, specimen: mechanical sounds good at the start, until halfway in, where the electric guitars sound like [[HellIsThatNoise '''ungodly screaming'''.]]

*** The music is also worth mentioning. specimen: patchworked sounds [[SoundtrackDissonance joyous and happy, unfitting for the situation]], specimen: organic has the sound of a heart rate machine (which seemingly flatlines at the end) accompanied by a horrid whirring noise that alternates between left and right speakers, specimen: paper sounds like something reminiscent of the [[Videogame/SonicCD Sonic CD US boss theme]], specimen: polygonal sounds like CreepyCircusMusic, and last but not least, specimen: mechanical sounds good at the start, until halfway in, where the electric guitars sound like [[HellIsThatNoise ungodly screaming.]]

*** The music is also worth mentioning. specimen: patchworked sounds [[SoundtrackDissonance joyous and happy, unfitting for the situation]], specimen: organic has the sound of a heart rate machine (which seemingly flatlines at the end) accompanied by a horrid whirring noise that alternates between left and right speakers, specimen: paper sounds like something reminiscent of the [[Videogame/SonicCD Sonic CD US boss theme]], specimen: polygonal sounds like CreepyCircusMusic, and last but not least, specimen: mechanical sounds good at the start, until halfway in, where the electric guitars sound like [[HellIsThatNoise *ungodly screaming.*

*** The music is also worth mentioning. specimen: patchworked sounds [[SoundtrackDissonance joyous and happy, unfitting for the situation]], specimen: organic has the sound of a heart rate machine (which seemingly flatlines at the end) accompanied by a horrid whirring noise that alternates between left and right speakers, specimen: paper sounds like something reminiscent of the [[Videogame/SonicCD Sonic CD US boss theme]], specimen: polygonal sounds like CreepyCarnivalMusic, and last but not least, specimen: mechanical sounds good at the start, until halfway in, where the electric guitars sound like [[HellIsThatNoise *ungodly screaming.*

* Axis' death in the Genocide Route. After a fight that mostly consists of you futilely shooting his garbage lid shield, he explains everything, including how he was the one to kill a human who came before Clover. Clover [[RageBreakingPoint fucking loses it]], and gains several LV while Axis watches in stunned horror. Then, you shoot a Big Shot at his shield, knocking it out of his hands before preparing a longer and far, far more brutal one to finish him off with. All the while Axis helplessly begs that [[ForcedIntoEvil he didn't want to do it]] and tries to convince you to spare him to no avail. [[NoKillLikeOverkill You demolish him with a massive laser from your SOUL]], and all that's left are a pair of bisected robotic halves just barely connected at the bottom to the wheel. It also splits open further as it falls. YouBastard

* If you discover the secret room in the Steamworks, you'll find an inhabitant how who hid themselves away to continue their experiments in secret, out of protest against the decision to fire those that worked there, and to keep themselves safe from the roaming robots. The room itself has nothing of note except a book titled "Mysterious Of The Underground".
** The first entry is pretty light, simply talking about the out of order arcade cabinet in the Oasis Valley Cafe, and its "unpleasant" contents… though it becomes less lighthearted when you realize it's a ShoutOut to ''Myth/{{Polybius}}''.
** The second entry, which is a bit more chilling, tells of a father whose child ventured into an area beyond the fences, and before finding them, described themselves in a daze, and seeing… nothing.
** The third entry, titled "The Phantom SOUL", however, is outright nightmare-inducing, as it goes into detail describing what happens to any human child that falls into the Underground, simply stating that they are "collected". But the real horror comes later, when it goes on to tell the story of a human child that was suddenly spotted in Snowdin, only for them to flee to Waterfall, and this being the last time they were seen… before their SOUL was mysteriously found in the deeper parts of Waterfall. This entry is so disturbing to Clover, they immediately put the book back, and if they later do a Pacifist Route, and make their way around Ceroba's mansion…
* While nothing scary pops up, if you decide to check the grave of Chujin,[[note]]the back side to be more specific[[/note]] you'll find a hidden tape with no label on it. If you decide to view it in the hidden basement, you'll see Chujin narrating again, only this tape's contents contains things you wish you never found… because it's ripe with [[FridgeHorror him sharing the hidden details surrounding the "The Phantom Soul" book entry, revealing that Axis had killed that human even though Chujin wanted to apprehend them (who is all but said to be the one with the Integrity SOUL)]]. This becomes even more disturbing when you realize that Axis was being built [[FridgeHorror before the attack, indicating that Chujin was]] [[FantasticRacism planning on dealing with humanity using them from the start]]. While Chujin was absolutely disturbed at the sight he saw, and even briefly considered stopping what he was doing, the attack simply gave him more motivation to go on with it, now having proof that Axis was indeed capable of what he originally intended. Also, with what Axis says on the Genocide Ending, it might have been possible that its programming thought that apprehension simply meant killing the human… [[SarcasmMode how thoughtful]].
** With specific Fun values, some of the Dark Ruins pillars can have drawings depicting Axis, the Integrity human, and a human SOUL surrounded by some sort of splatter. Notably, the pillar with the human drawing is damaged where their face would be, raising the possibility that Axis ''blew the kid's head off''.

* If you have the right FUN value, then when going through Snowdin, you'll end up in a mystery room with a monster named Jane, who talks about how monsters have been randomly going missing. Talk to her a second time, and she remarks that someone has to be responsible. And the moment you leave the room, you can't come back.

** The first entry is pretty light, simply talking about the out of order arcade cabinet in the Oasis Valley Cafe, and its "unpleasant" contents… though it becomes less lighthearted when you realize it's a ShoutOut to ''VideoGame/{{Polybius}}''.