1 - 20 of 98 Works in True Lab (Undertale)
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This is about Alphys and the True Lab, except instead of entries, she writes in a diary. And with added guilt! All of this is based on lore, so please read if you already know the lore of undertale. (i know this is a terrible summary throw stuff at me all you want)
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What was life like for the underground before undertale? Where did the skeleton brothers even show up from?
And why are Sans and Alphys good friends? That is what this fic aims to answer.
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A Former Royal Scientist’s Research of the Space Time Continuum by stitchthelilo
Fandoms: Undertale (Video Game)
26 Jan 2026
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A little bit of rest during her research could definitely hurt, yet her eyes began to shut anyway. The consequences to this were much more dire than Queen Alphys could’ve ever expected, and after an abnormal earthquake she finds herself stuck within the endless Multiverse.
And for some reason Sans is.. everywhere??
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Takes place right after the Alphys Neutral Ending, where a freak accident sends Queen Alphys - better yet, just Queen - out on a travel through the Multiverse.
Series
- Part 2 of Longfics
- Part 1 of A Former Royal Scientist’s Research of the Space Time Continuum
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Heartrot /noun
any of several rots involving the central part of a plant or plant organ: such as disintegration of the heartwood of a tree
Are they keeping each other's secrets as a duty to a friend? Or are they keeping them because they are implicated in each other's lies?
Either way, neither Alphys nor Mettaton can deny that what remained of their friendship lies dead and rotting between them.
When tensions and emotions run high and they face their resentment together, will a desperate fight for intimacy bring them closer? Or will it be the nail in the coffin of this twisted friendship?aka my beloved Alphys-Mettaton hatefucking fic
Series
- Part 26 of Kink/Whumptober 2025
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Know any good chemistry jokes? NaBrO. by PapyrusFanatic95
Fandoms: Undertale (Video Game)
18 Dec 2025
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The power goes out in the lab and Alphys is reminded of some not-so-good memories. Sans comes in to hang out and comfort her.
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Desert Sanctuary Guidebook by KarmaSpidr
Fandoms: Undertale (Video Game), Undertale Yellow (Video Game)
26 Nov 2025
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Clover doesn't give up his soul because justice still needs to be delivered.
The Wild East, and later practically the entire Dunes, declares independence. They declare that any human within their borders is under their protection.
Civil War looms over the Underground.
Would you like to see what happens?
Note: This is NOT a story. This is an archive containing information about my AU, Desert Sanctuary. I might write a proper story in the future, but for now, this is where you can read about the narrative, the characters and how this massive change affects Frisk's journey.
Fanart and other fan works based on Desert Sanctuary are welcome and encouraged
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A FINE LINE BETWEEN ORANGE AND YELLOW - Hiatus/Rewriting by MairwynCSulien1990
Fandoms: Undertale (Video Game), Original Work
07 Nov 2025
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While Aneira didn't necessarily believe monsters existed, she did find the fact that everyone and their dog still did might mean something. Her childhood town of Beddgelert believed in monsters trapped under the mountains near their home that would need a seventh soul now to break out and destroy lands.
Putting this on hiatus because not only do I feel I can characterise Aneira better (writing characters in character is not easy for me), the general plot can do with reworking and yk foreshadowing. Might just reupload chapters once I've completed the story, which may actually get me to update something in a reasonable time frame.
Do not expect anything to be done soon because I am going to be very busy very soon and won't have the time until the Christmas holidays.
Sorry, not sorry, I want something I write not to weigh on my mind how badly written it was, less so than usual - this note is mainly for the singular friend that follows me and may actually read this.Series
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Encounter Unjust by Thaxonyn
Fandoms: Undertale (Video Game), Undertale Yellow (Master Sword)
28 Oct 2025
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When one Human does something unjust, another Human decides to try to take care of it. (See notes in Chapter 1)
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Sakura Don't Usually Come in Indigo by CouldntThinkOfUser, Rivetsagoner (CouldntThinkOfUser)
Fandoms: Undertale Yellow (Master Sword Video Game), Undertale (Video Game)
02 Oct 2025
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Kanako Ketsukane - Age 10 - Admitted into Royal Scientist Alphys' care on the Thirtieth of September, 2008.
Has not seen home for about a year, does not like how her body is all melty and gooey and dull and blue around her like twigs and she's all long. And absolutely does not like how That Human's voice is in her head.
Adrian Valentine 'Indigo' Harris - Age 11 - Killed on the Third of May, 2001
Feels numb, but feels everything. Knows he screwed up, even if they started it for the most part. Wants to make amends with Kanako, but this fox he indirectly traumatized keeps curling up into herself. And why is she so tall?
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Undertale: What Honesty Feels Like by Virtue_Of_Dragons_Dreamer
Fandoms: Undertale (Video Game), Undertale Yellow (Master Sword Video Game), Deltarune (Video Game)
16 Sep 2025
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This story is set in an Alternate Timeline that branches off before the events of Undertale. Sitting in the True Lab, Alphys gets an unexpected phone call from Undyne. When confronted by the captain about her secrets, Alphys chooses to be brave and tell Undyne everything. But honesty doesn’t mean the road ahead will be easy. Can she hold onto that Bravery when her attempts to fix her mistakes unleash something horrible?
Series
- Part 1 of Virtue’s Underverse Stories
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GOOPY KITTY // AMALGAMATE MAD MEW MEW AU INFO by silverstormsxx
Fandoms: Undertale (Video Game)
18 Aug 2025
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what it says on the tin.
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W. D. Gaster: the Heart, the Brain and the SOUL by WittyWind
Fandoms: Undertale (Video Game)
13 Aug 2025
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“The weight of the head of a genius is equal to its value.”
W. D. Gaster didn’t want to admit it, but he could feel it, deep inside him.
His brilliance gave a future to the Underground, a machine that could convert the heat of the Earth into energy: the CORE. The other monsters would, then, use it as electricity, and bring life to their houses and their TVs and their cars and their cell phones.
But Gaster knew more. Knew better. The CORE had so much potential, so much to offer. That kind of magic had never been used before. Gaster didn't know if he could call it “magic”, even.
He was so valuable to the Underground, but… what if that made him dangerous? What would happen if he had discovered something that shouldn’t be touched, not even by monsters or humans?
W. D. Gaster didn’t want to think about it, but he could feel it, deep inside him.
What is the value of a genius, if he’s so terrified of the weight of his own head to ever use it?
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This is my first fic! I'm so excited! I'm open to any criticism, tips, and please tell me if you see any typos. I'm very scatterbrained so things might not make sense plot wise, there's probably things I'll forget to add, but i hope anyone reading enjoys it!
2S3-A, or rather, Bunker, expected to die when Gaster dropped him off in the middle of an active Battlezone and... well, the details get fuzzy after that, but he's sure Gaster activated some sort of kill-code. Bunker just... he's so tired. things cant possibly get worse. can they?
Frisk had been tracking the movement of 2S3-A since the very moment the monsters emerged from the underground three years ago. something about him was unsettling, his whole existence wasn't right. but she never could put her finger on it. until now.
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Chara and Frisk come across the VHS room of the True Lab, and Chara prepares for the worst.
There's only one problem. Or a temporary distraction, depending on how you look at it.
Frisk doesn't know what a fucking VHS tape is.
(loosely inspired by Spirit of the Underground by GreenieGirliePop!)
Series
- Part 3 of charisk oneshots :]
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You fell chasing your little sister. Now, disguised as a monster, your gambling everything to get Frisk out alive—including trusting a lazy skeleton who sees through her lies. With Asgore’s knights closing in and the king needing one last human soul, survival demands shortcuts through glowing caves and MTT Resort glitter. But Sans’s bone-dry wit and hidden power blur the line between using him… and losing your heart underground.
Neutral Route | Slowburn Sans/Reader | Found Family | Protective Siblings | 2016 Undertale fic vibes
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Frisk enters the True Lab, and well… they certainly don’t like what they find.
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After everything went to black, Clover asked themselfs if this was how death was. If they had anyone to wonder.
It was too dark to see, too silent to hear, too empty to even think about it. A little more and they could feel the cold, hard glass of the container they're inside, trapped for who knows how long. It could be hours, it could be days, or it could be centuries.
It feels like centuries, until it doesn't.
And a dark, misterious ceiling with a light too bright welcomes them. It's not a warm welcome.
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What if everything you knew and loved crumbled around you, and all you could do was sit and watch? What would you do if your friends all died, and the most you could do was watch on a big screen?
These memories were no blessing, not at all. Even if she could warn them, she had to die over and over and over and over and-
It just.. wasn’t worth it, it never would be, not to Alphys.
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Alphys begins to remember resets, and she wished she didn’t. Oh how she wished she didn’t.
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As the Royal Scientist of the Underground, Doctor Gaster was used to being given various tasks by the king of the monsters, Asgore. The first of them since they had all been sealed underground after the war was to help monsters settle down into their new home. And the second of them had been to establish a more consistent power source for monster-kind. Of course, the Steamworks had originally been developed to do the same thing, but the power it provided wasn’t nearly enough to cover all of it.
Over the course of several years, the Royal Scientist had designed the CORE and had it built, a much larger version of the Steamworks that managed to successfully run power through the entire underground. And it wasn’t even like his position had only been granted to him after being sealed underground, he’d been working for the king and queen for what must’ve been at least a century. Pros of being a monster who’s yet to have children, he supposed.
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A short story about W.D. Gaster prior to falling into his creation.
Series
- Part 1 of Undertale/Deltarune Fanfics