#papyrus is gaster theory

[dsco-kjs]

He found you.

Don't mind him, he's just testing his new flashing light without using hands!

@forgettable-au

[agere-infection-au]

Character reference sheets!

Part 4. One missing, one infected

Lust : *Very fast and indecipherable babble-explained MLP lore*

Epic : Can I have another glass of chocolate milk? It'll be last one, I promise! (It was, in fact, not last one)

Papster : You sure you have taken an account of all knowledge of infection so far?

Previous | First | Next

[thetiredlazybones]

Since you are aware of Aus, what do you think of the ones that follow the premise “Papyrus was/is Gaster”? I’ve seen some and I gotta say they are pretty interesting! But I would like to hear your thought on this

[luna--dragon]

Collected a bunch of evidence for... whatever this theory is called? Saw a bunch of people talking about it online and got bored, so I made these.

[zarla-s]

A Patreon request for a Gaster version of that old shot of Papyrus in a duplication machine. Brothers are very confused!

[index] [comicfury]

[forgettable-au]

I just realized I never mentioned I was taking a break from the comic to focus on the new deltarune chapters oops

But that's over now and I think I'm gonna come back to working on this soon <3

Sooo, expect me answering a LOT of asks soon!!!

And then I'll continue working on pages

[maxladcomics]

Undertale: 17

(Directly related to the Undertale: 3 post)

This Amalgamate is made of 17 monsters

Entry Seventeen (17)

17 Monsters in Snowdin (Papyrus is the 17th)

When you're at 3 HP or less, the Bad Memory heals you. So it'll heal you if you're -17 HP.

The only monster with 17 in its stats

-17

On Papyrus's 17th attack (this line) his attacks will be random (His is the only battle that does this, I checked them all. Asgore's battle becomes random after 20 turns)

[caliburnabsolute]

One for the road.

Let's cherish this last day of pre-Chapters 3&4 speculation while we can, alright? Deltarune is waiting.

[sabrepanther]

Ok, so I've been thinking about the egg & tree rooms in Deltarune. Each are located in "in between" spaces where we find a "forgettable" man. The game seems to make a big deal about "in between" states of being, where lost things fall between the cracks and are forgotten.

Guess WHO else in hometown talks about "in-between" states of being?

THIS MOTHER-BEFRIENDER

AND he just happens to have a brother who is described as "forgettable" in UT's no-mercy run flavor text. During Papyrus's date, an egg shows up on the "dating" hud. Now I'm not saying that Papyrus is 100% the forgettable man, BUT something is going on here with the skelebros.

Thoughts guys?

[hopefulleafva]

Papyrus Wrote the UTDR Mystery Valentine

Okay so with a 2025 release for Deltarune chapters 3&4 confirmed I want to get this off my chest and document it for future me to either feel vindicated by or have a good laugh at how wrong it was. This has been eating me alive since the Valentine’s newsletter and I never said anything but I want this out there before anything new comes out.

Disclaimer: I have no idea if this is a theory other people have already made posts on or not because all I ever see is “it’s Gaster!” or “It’s not Gaster, it’s Dess/Egg Man/[Insert mysterious character here!]”. If someone has posted this theory before I missed it entirely. Not looking to steal anyone’s theory thunder here.

I’ve convinced myself this is Papyrus and just want to get my thoughts down here.

So. I see a lot of people talk about how the flippant and humorous way it’s written makes them think this isn’t Gaster. To get the Gaster stuff out of the way, my stance is that everyone has their own preferred idea of how they think Gaster acts and whether or not he could have a sense of humor, but we really have yet to learn a lot about him in canon. I don’t love us trying to make rules about what is and isn’t “in character” for him when we really haven’t met properly and have very little dialogue to go off of. I get a lot of people are basing their ideas of him being serious off Entry 17 and the popular assumption that the intro voice is Gaster. I think that’s fair and very understandable, but even still it’s only an extremely limited peek at what the guy is like. Point is, maybe he does have a silly sense of humor and maybe he doesn’t. I don’t want to entirely dismiss the idea that Gaster wrote this based on “it’s too silly, Gaster is serious!”. But I also think that the idea that because the speaker is a mysterious voice with meta knowledge of Deltarune that it MUST be Gaster is also a bit shaky.

Anyway.

Is it just me or does the bizarre roundabout way of phrasing things in the letter perfectly fall in line with how Papyrus speaks?

One of my favorite notes in the Undertale Legends of Localization book (HIGHLY recommend by the way, a really fascinating read) was this:

While yes, it’s important to bear in mind that this was the quote of a localizer and not Toby directly, I think it still rings very true for Papyrus’s character. Don’t really think I need a laundry list of examples for this point, right? Papyrus’s fun and unique way of speaking is such a memorable part of his character that you encounter in all routes.

Which is why it’s so interesting to me that this mystery writer seems to have a highly similar way of phrasing things in a unique and playful way.

The first one that really sticks out to me is the “I never forget someone I don’t remember.”

Really reminded me of the little bit you get after a post neutral run reset.

While not something I originally weighed in to my theory, it is worth noting that this bit between Papyrus and Sans occurs immediately after Papyrus has recognized Frisk after seeing them for this “first” time. This makes the mystery valentine writer’s preceding comment that they will know the forgotten person they are looking for immediately upon seeing them extra interesting.

This bit also stood out to me:

Because it also felt like very familiar phrasing. It took me a while to realize what it was making me think of.

Down to the quotations around a common phrase like it’s an alleged thing not a very common thing??? Like MAN.

While these were the only two parts I felt directly and strongly paralleled specific phrasing Papyrus has used before in canon, there were a few other things that caught my eye.

A faith in the power of love, and the power of belief.

(Yes, I realize the “even if you don’t think so” appears to negate the idea of Frisk’s beliefs being an important part of their ability to change, but I’d say Papyrus is still emphasizing that his beliefs are significant in this.)

Very strange that the writer doesn’t dismiss the idea that the person they have forgotten they wanted to help could be themself. How could you forget yourself? But then again…

And while not really the same degree of strength in a parallel, I just want to bring up that the letter writer remarks that the reader is odd yet reliable for responding out loud to a piece of written communication.

It is strange that the author seems to have still heard the reader’s out-loud reply to the letter. A weird instance where a mode of communication that has limits on what SHOULD be able to be perceived by the other person somehow has those limits broken and allows that person to comment on something they shouldn’t be able to perceive.

Kind of like if you were having a phone call with someone far away from you but they still seemed to somehow be able to know exactly what you were looking at and where you were. Where have we heard that before…?

Also come on. You can’t tell me “PUT ON YOUR COAT AND WASH YOUR FACE! OR, PUT ON YOUR FACE AND WASH YOUR COAT. NOT NECESSARILY IN THAT ORDER. OR, IN ANY ORDER AT ALL.” doesn’t sound like a Papyrus-ism.

I know some people may point out that Papyrus already has Valentines that are very explicitly from him in the newsletter, so it would be weird to have three that are and one that wasn’t. But I don’t think that necessarily should refute this idea. It could be possible the “signed” valentines are from Undertale’s Papyrus, and this one is from Deltarune’s Papyrus. Even if you subscribe to the idea that UT Papyrus IS DR Papyrus, this could simply be a letter sent from a different point in time.

Anyway, this has been eating me alive since February so I wanted to get it off my chest. Maybe this is completely off base, but interesting to think about.

[dissasembled-ink]

Honest thoughts and theories of Deltarune characters so far.

I won't make any fancy intros, I'll get right to it:

Roaring Knight -

I think Roaring Knight is pretty much in a way confirmed to be Dess Holiday, Knight is left handed, Dess is left handed, those are fairly specific odds especially since Dess is not yet present in the game, Carol gets very angry when someone aside Kris touches Dess's stuff.

If Knight is Dess then: may be a mutated, corrupted dark form that can be powerful enough to kidnap Undyne and then speak on the phone about a sacrifice. Of course, being fully conscious and aware of the actions they do.

Kris -

I think Kris is not only in on it, but somehow, being a puppet of The Roaring Knight. Why do I think that? Well, Kris and the soul are very much the same person no matter what we do, Kris seem to not mind unless it's the secret of the shelter. Kris actually formed a bond with Susie, Ralsei, Noelle willingly, we as a player didn't forced them into it, proof is, if you wait in the wardrobe with Susie and Noelle talking, yellow text does trigger Kris's reaction and not usually in a bad way, occasionally blushing to some reactions, not immediately out of embarrassment, but maybe out of flattery as when you speak of Kris being good at flirting, which undoubtedly is our, the Player's cause, Kris seem to not be angry of it, but talking about their skills also triggers the same reaction AND if we wait long enough, Kris enters a state I would describe as trying to catch a breath as without the soul they are very much dying. In the library we find out that the Soul and Human are connected, but Kris and the Soul had to somehow disconnect from one another forming us, the Soul and separate cold and distanced Kris. (A darker theory is that Kris died and we are the soul of someone else giving Kris life for the price of taking control of their body occasionally, but that I find to not make much sense.) However Kris does act on their own, seeing in Chapter 4 where they simply took a breath, without the need of pulling out the Soul they played the piano the way they can do as, let's be real, next to Kris we suck at piano, but both are actually completing one another in things, we socialize Kris more and give them friends and they well...do anything Kris can do best, be spooky, distanced and play very well on Piano (Okay I know Kris is good at a lot of things, I just thought it'd be funny if I said this XD)

Ralsei -

Ralsei is definitely hiding something, theory has it that Ralsei is the horned headband we still probably carry around or is an embodiment of memory on Asriel who will arrive at the city fairly soon, maybe sooner than we thought!

Prophecy seems to indicate someone's sacrifice, what I think this implies is however that all Dark Worlds need to be sealed and only then the Light World is completely safe from The Roaring.

Noelle/Susie -

Somewhere was apparently an indication of the second protagonist next to Kris to be Noelle, however the evidence is fairly weak, but I shall include it here nonetheless, in a year we will return to this and laugh maybe!

Asgore -

I know Asgore seems fairly innocent, but as I replayed Deltarune I kept noticing that- there's something off about Asgore. Why would Toriel leave him over a FLOWER business?! That makes little to no sense. So I think and most likely some of you too that Asgore has a deeper secret and because he couldn't share it with Toriel, Toriel felt betrayed, like he didn't trust his own wife enough, however I think he again, does bad, but means no harm, has actually pure intentions and is just misunderstood. Poor Asgore in this case is getting again cucked by a funny skeleton. (XD)

Gaster -

Although not appearing as of yet, let's go over the evidence. Dark Darker Yet Darker used to play around The Shelter, "Garbage noise" is the Entry Number 17 and nowadays people point out that a little alignment here and there and The Titan looks eerily like Gaster's face.

My theory of Gaster however: Gaster might be but a Darkner in one of the Chapters, maybe a secret boss with a lot of questions of his own, who knows? People anticipate Gaster so much, I think the game would probably get scorched by the toxic side of the community that wants to see the funny goofy man who speaks in hands.

Importance of previous main bosses of Undertale -

There might be little to no importance of characters like Sans, Papyrus, etc. as the story doesn't include them aside puns and Toby giving in on the Toriel x Sans shtick, however again, I believe this will not become a thing as Toby has a history of this type of humor and it is funny so far, ngl. Again we need to realize that Sans, Papyrus, Alphys, Undyne...their story is already written elsewhere, their personalities, etc. and it makes you feel more for the characters, despite them being less than a background noise which I find genius from Toby's side, however there's still 3 more chapters so...the reality can still be completely flipped, expect the unexpected in this case.

Importance of secret bosses of Deltarune -

Well we seem to have an interaction between Tenna and Spamton, seems that their importance is only going to increase as talks about them...aside probably the Knight as he is not really a secret, but one of if not the MAIN antagonist of the game.

Jevil - Mentioned by Spade King, Seam and many more in the respective chapter Jevil's included and it's getting more frequent as time goes by.

Spamton - Honestly? He was already a big talking point in the Cyber World, he was like Gaster, but debunked, only others didn't saw him often if at all, aside us and then Susie and Ralsei.

Gerson Boom - Thanks to this boss fight we also learned something, plus it gave us a clue. Dark World can, even if temporarily, resurrect the dead. Gerson is but dust in Alvin's office and yet because it's in the church we are able to communicate with him and he seems to be...himself. Which may be a very own plot device for the antagonists to work with, we'll have to find out.

The ritual -

Something is off about this one. Kris studying occultism, Knight spoke of sacrifice and ritual, Undyne kidnapped for it, Asgore's 7 magical looking flowers, Kris's divided soul between now us and Kris themselves instead of JUST Kris. I think they want something else than to bring The Roaring. Why would Carol, Asgore, Undyne, Dess and Kris want to destroy the world? Even if we divide them character by character, Carol has Noelle, Rudy and maybe still Dess somewhere she most likely cares about. Asgore? WELL LOOK AT THE GUY! He's a lovable dude who would probably put his life at risk for his family. Undyne? Why would Undyne want to destroy the world? She's a natural born hero! Dess and Kris? Even in a gothic phase you would chicken out of something like destroying the world over something stupid. Plus they're not little anymore to not have rational thoughts...unless we take in consideration Kris is broken and Dess probably corrupted, but HEY! You don't have that from me!

Are we the villain all along ?

Honestly, possible, I given it a thought, no matter what side we're on, what route we take, we're still most likely controlling someone against their will on many occasions. Weird route? Yeah that one- is weird, but all the more strange to think that the reason Kris was spooking Noelle in the past might be because of the Soul? Hmmm, maybe, maybe not.

What I think with Kris is that there's like- 75% chance Kris is a good person, has noble intentions as even if Noelle's and Kris's friendship was forced, Kris seems to always care about 2 people in his life so far, at least most discussed. Asriel and Dess. The world and Deltarune practically revolves around them and we're like that nervous cousin, getting ready to meet and greet them.

It's possible what's going on is still way too large for us to assume and we'll have to really wait until 2026 for the next Chapter 5 to give us answers so we would get to the bottom of this in Chapter 6 and 7. I don't want Chapter 5 to be some kind of filler, ending on a cliff-hanger, just because it's only a year away, I really hope Chapter 5 will explain a lot if not the most so we could focus on HOW to get a desirable ending than "What comes next after a year or two?" At least some answers would fit as Chapter 3 and 4 explained little and opened MANY more questions than it answered.

What we know so far (?) -

Dark Fountains can be opened if you have a strong will to do so, not anyone can do it, you really need to try is the way Chapter 4 interpreted it.

Spamton's secrets of Mike are more or less fully explained and serve little to no importance. HOWEVER. It brought a theory (not Mike, but Spamton and Tenna). Spamton is unrecognizable to Tenna, it's not just Tenna ignoring him as he wished to see Spamton, but when Spamton shown, he got "frozen" by Tenna who didn't knew him. The phone call that changed Spamton's life for worse is still on the table as it was not with Tenna, Mike or anyone we yet know. Maybe Gaster? Maybe Kris without Soul? Maybe Roaring Knight? Maybe secret boss of one of the upcoming chapters? Time will have to tell.

Seam for a reason he doesn't wish to share betrayed Jevil and sealed him over The Roaring Knight dispute as Seam seems to be a magician, said by the Spade King. Will Seam betray us? Or is he just going to make us that strong weapon?

Shadow Crystals are a part of The Roaring Knight maybe as yes, we got the shard from the chipped sword, however, we also got a shadow crystal. WHAT does it imply? Maybe I'm overthinking this one though.

Dark Fountains are able to bring back memories of OR the dead themselves back to life. I am not implying Ralsei is dead Asriel, but might be a said memory of Asriel the way Kris remembers. Until Asriel comes back from College we know barely anything of that being true or false.

Kris and The Roaring Knight know each other, they secretly communicate, upon no-hit running The Roaring Knight, Kris gestures that they should speed the fight up, seems like in that sense Kris is showing awareness that the Knight is taking it lightly on us as he recognizes Kris. Either a co-operation or something more. Maybe who knows? Grand twist of the said knight being Asriel or Asgore. Reality can be anywhere again as Toby has the cards and we're just waiting for his play here XD

Gaster is not yet HERE FFS, we're in the middle of Deltarune and we still don't have the funni goop man nor Papyrus, but we have one more Dog sequence where we own him at climbing and he fucking dies XDDD

If I left something out and you would remind me of it, I will include it after EDIT title below all this text lol.

[not-ishmael]

A Revised (not so) Brief Study Into The Nature Of Deltarune

Disclaimer: This is a revised version of a theory I came up with back in 2022, having played just the first two chapters. Now I'll take into account chapters 1 to 4.

TL;DR:

For some time I've been quite intrigued by the appearance of some very particular leitmotifs that Undertale's and Deltarune's OSTs have in common. This took me down a rabbit hole that brought me to the realization that it's quite possible that DR Sans and UT Sans are one in the same, and the Reset Theory on Deltarune is probably right.

This forces me to believe that Deltarune is a prequel from the perspective of the characters, and a spiritual sequel from the perspective of the Soul/Player.

The Pre-Sequel Theory

First and foremost, pardon my English. It's not my first language and sometimes I mess up.

Secondly, this is a LONG post. There's a lot –a LOT– of text and no images at all to ease the reading. I advice jumping into it only if you don't have anything better to do for a bit. The PDF I first wrote this on is 6 and a half pages long.

Index:

Motivations.

Clues in Undertale.

Clues in Deltarune.

The Delta Rune.

Blood.

Conclusions.

Problems with the theory.

1 Motivations:

I've always been fascinated by soundtracks and ever since Undertale came up, its soundtrack wasn't an exception.

More recently I've been a bit more focused on the leitmotifs that Toby Fox uses in both Undertale and Deltarune. As many people noticed, they share a lot of common themes. For many of them it's easy to understand why (for instance, for common character's themes, like Sans', or the theme for Justice) but for some others it's not that simple.

Assuming that this commonality in themes was proof of a direct relationship between the games, I tried to study its nature and what elements outside the soundtrack can be used as evidence of this connection. This brought me to Sans ,because of course it did.

Trying to validate these assumptions took me down the rabbit hole that theory crafting around Sans has always been, and the musical side of my reasoning ended up being but as small part of the whole proofing. Regardless, I'm quite happy with the result, albeit it's not free of problems that I'll address and discuss at the end of the post.

With that out of the way, let's begin by talking about small details that Undertale gives us, and how it hints us that its past is somehow connected to Deltarune:

2 Clues in Undertale:

There’s a lot of non-music related hints that point towards a possible connection between both games in Undertale. Here's a summary of all the hints found within this game:

To begin with, there's what we know about Sans' backstory:

Both him and Papyrus appeared one day in Snowdin, seemenly out of nowhere.

In Sans’ lab there’s a broken machine and a poorly drawn picture of 3 people we don’t recognize, with the words ”don’t forget” written on it.

Sans insists a lot about about how he gave up trying to go back (somewhere, sometime, or both).

On the other hand, there’s the famous Gaster’s Entry 17, that could imply some knowledge of the Dark Fountains by the former Royal Scientist. Another Gaster related piece of evidence is goner Clam Girl. Soon before the release of Deltarune Chapter 1, in the Switch version of the game, Clam Girl would turn into a goner and say that the time to meet this Suzy ”... is fast approaching”, before disappearing with the sound Mystery Man makes when disappearing himself. Although Suzy is not written the same way as Susie, there’s no reason to believe that Clam Girl is not talking about Deltarune’s Susie. This not only hints to Undertale and Deltarune being connected, but to Gaster being behind the whole connection, since she turns into a goner sprite and disappears the same way Mystery Man does. I know Mystery Man is not confirmed to be Gaster, but it’s definitely related to him in someway.

There must be something going on with Papyrus as well, since he’s Sans’ brother and comes to Snowdin with him, but in Undertale he doesn’t seem to be as knowledgable as Sans. Since Papyrus doesn't bleed, as does Sans, maybe they're different in some way, and don't share as big a past as previously thought.

2.1 Sans’ lines during combat:

During the fight against Sans, nearing the end of the Genocide Route, we get some snippets of his backstory within his lines of dialogue. He begins, after the Player’s first attack, by saying:

our reports showed a massive anomaly in the timespace continuum. timelines jumping left and right, stopping and starting...until suddenly, everything ends. heh heh heh... that's your fault, isn't it?

We don’t know who is he working with, but it seems they know very well about the power to control the timeline, since they were monitoring it.

Sans continues with:

knowing that one day, without any warning... it's all going to be reset.

look. i gave up trying to go back a long time ago. and getting to the surface doesn't really appeal anymore, either. cause even if we do...we'll just end up right back here, without any memory of it, right?

to be blunt...it makes it kind of hard to give it my all.

In these lines we get a bit more information. Sans is –understandably– depressed about the whole reset situation, but mentions ”going back” to somewhere. We know it’s not somewhen because he doesn’t remember earlier timelines –besides the occasional déjà vu– and it’s not the Surface, since he mentions it right after that line. So, where else would Sans be trying to go back to? It can’t be anywhere in Undertale's universe, since he can move freely through the Underground –even through teleportation– and he specifically states that it’s not the Surface. Thus, it can only mean somewhere outside this universe.

A bit after that he continues with:

all i know is... seeing what comes next... i can't afford not to care anymore.

What does he mean by ”seeing what comes next”? He doesn’t know the future, nor what the Player did in other timelines. So, what is he talking about? Back in 2022 I had no clue what he could be referring to. Now I'm inclined to think of the Roaring, or the End of the Prophecy.

2.2 Sans’ secret lab:

After Sans gives the Silver Key –which happens to be a reference to a book about timetravel by H.P. Lovecraft– to the Player we can access his Secret Lab, hidden underneath his house. Inside of it we find:

A covered up broken machine.

Blueprints for a machine written in un- readable symbols.

A badge.

A photo album with:

A picture of Sans, happy, with other people the Player doesn’t recognize.

If the Player already fought Asriel: A second picture appears, showing Sans, Frisk and their friends.

After the v1.001 patch of the game, if the Player has talked to Clam Girl and knows of Suzy, from the back of the photo album sticks out a poorly drawn picture of three smiling people with the words ”Don’t Forget” written on it.

The first three items, although interesting, don’t give us much to work with. The machine is covered up and the blueprints are unreadable. The badge could become another huge hint in the future, if during Deltarune’s festival Sans happens to win a badge for winning at something. But this is purely speculation so I won’t be taking it into account –for now–.

The pictures and the drawing, on the contrary, give us much more information. Let's discuss them a bit more in depth:

2.2.1 The photo album:

By the time the Player gets the Silver Key, possibly after the battle with Asriel, they (and Frisk) have met every main character in Undertale’s story. Thus, the people in the first picture, who neither the Player nor Frisk recognize, can’t be anyone we know. They could be random people from other places in the Underground Frisk hasn’t met –although, from a storytelling perspective, this doesn’t make much sense– or they could be from Deltarune's universe -which makes a lot more sense storywise-.

Furthermore, there’s the poorly drawn picture. Since this picture only appears after talking to goner Clam Girl, a character heavily tied to Deltarune -specifically, to one Deltarune Character-, and it has the words ”Don’t forget” –words that don't mean anything special in Undertale, but are extremely important an present in Deltarune from the very beginning– written on it, it’s safe to assume that the three poorly drawn characters are a trio from Deltarune. Due to Frisk not recognizing them, they have to be characters that only appear on Deltarune. What trio of characters do we know from Deltarune that fit these characteristics? I’m fairly sure Kris and Susie are two of the three, but the third is a bit more complicated. My first suspect was that it was Ralsei but, since he’s a darkner and he can't go into the lightworld, it can't be him. My other candidate are either Noelle or Dess, since Berdly dies in the Snowgrave route of Chapter 2 –and Toby Fox likes to keep all possible endings as canon– and we don’t know of any other important lightners that don't appear in Undertale as well.

2.3 Darker, yet darker:

Gaster's Entry 17 states:

ENTRY NUMBER 17, DARK, DARKER, YET DARKER, THE DARKNESS KEEPS GROWING, THE SHADOWS CUTTING DEEPER, PHOTON READINGS… NEGATIVE THIS NEXT EXPERIMENT, SEEMS VERY, VERY INTERESTING… WHAT DO YOU TWO THINK?

At the beginning of Chapter 3, Ralsei explains to Susie that the Dark World is what happens to reality in the total abstence of light. When it's darker than dark. Darker, yet darker. So dark you could take away the light that wasn't there: photon readings... negative.

It's now that we can say, with absolute certainty, that Entry 17 talks about opening a Dark Fountain within Undertale's Universe. And Gaster, to whom we talk to outside the Deltarune chapters, is responsible for it.

I don't really like to get into Gaster while theory crafting. Sans is enough of a controversial rabbit hole for me. But after Ralsei's exposition in Chapter 3, I can't look the other way.

The connections between WD Gaster and Sans run deep. Not only are they 2 out of the 3 characters whose speech is characterised by the font that names them, but UT Sans' infamous attack is called "Gaster Blaster". Furthermore, it's known that Sans and Alphys shared a past, and Gaster could be this missing link between the two of them. Could it be that Gaster is referring to them at the end of Entry 17? Hard to say, and we can only speculate. But it would make sense that Sans, if he had come from Deltarune's Universe, would try to study Dark Fountains with the Royal Scientist and his pupil, as well as the passage of time, as evidenced by his comments during the fight against him at the end of Undertale's Genocide Route. It would also explain what he meant by "i gave up trying to go back a long time ago". He gave up researching the Dark Fountains after Gaster was consumed by the experiment and scattered through time and space.

3 Clues in Deltarune:

Back in 2022 I had only played Chapters 1 and 2, a quarter of the game. Even though this wasn't much content to work with, the leitmotifs Toby Fox used gave us a lot of information.

3.1 A brief introduction to leitmotifs:

*This part is skippable if you know what a leitmotif is*

For those who don’t know, a leitmotif is a small piece of melody that appears many times in a composition, and is associated to a character, a place, or an idea. Examples of this are the main themes of characters: a simple, recognizable melody that is associated to a specific character. For instance, the main melody in Nyeh Heh Heh!, which would be Papyrus’ leitmotif, or the common themes in Spear of Justice and Hammer of Justice, which would be Justice's leitmotif.

Soundtracks are rigged with leitmotifs, and neither Undertale’s nor Deltarune’s soundtracks are an exception. Since each one is associated to a specific character, place or idea, the use of the same ones in both games is something to keep in mind.

3.2 Leitmotifs that appear in both games:

The first song that plays inside Deltarune's , in Chapter 1, is Beginning, which has 2 leitmotifs in it: Once upon a time –from Undertale–, and Don’t Forget, –from Deltarune–. This second leitmotif appears in several other songs in all chapters.

The song that plays in the menu after you finish Chapter 1 is called Before the Story, which has the exact same melody as in Once upon a time. This leitmotif is one of the most –if not he most– used in Undertale’s soundtrack. For me, it’s kind of the ”Undertale theme”, for how much it appears in the game –same as Don't Forget would be Deltarune's theme–.

There are some other Undertale leitmotifs in Deltarune’s OST that I won’t be taking into consideration. These are the character’s leitmotifs, like Sans’, and other that represent important emotions like Determination, Justice, Despair and Hope –These leitmotifs are a bit difficult to recognize if you’re not deep into the music side of the games. Determination can be heard, among others, in Undertale’s Determination and Deltarune’s Rude Buster; Despair corresponds to the melody in Undertale’s Burn in Despair, and appears in Your Best Nightmare, Vs. Susie, at Queen’s basement, right before the Spamton NEO fight, and again in Chapter 3's Bit Roots; Justice is heard in Undertale's Spear of Justice and in Deltarune's Hammer of Justice, and Hope is sometimes called ”Snowdin’s theme”, which is used in Undertale’s Snowdin Town and Hopes and Dreams (thus why I prefer to call it Hope’s leitmotif) and in Deltarune’s A Town Called Hometown–. These leitmotifs being in both games is to be expected, since they either represent common characters or common emotions to both games, and Toby likes to reuse leitmotifs from old projects, so they're not really relevant to the theory.

Going back to the theory, the use of the words ”Don’t Forget” as a title for the most present leitmotif in Deltarune is a bit on the nose, taking into account the poorly drawn picture in Sans’ Secret Lab. The soundtrack acts as a constant reminder to not forget –pun intended– that drawing. But this isn’t the only insinuation Toby left in the game’s music. There’s another, much obscurer, clue: the name of the song Before the Story. Since it plays at the menu only after you play Chapter 1, it can’t be referring to ”before the story” of Deltarune, since that story has already begun. So, what if the Story is Undertale’s? If so, since it uses the most important leitmotif of Undertale in a song called ”Before the Story”, this would imply that Deltarune’s story happens before Undertale's.

Back in 2022 this was enough proof for me to be convinced of this theory. And yet, in 2025, it rained.

3.2.1 It's Raining Somewhere Else.

What is there to say about this. What is there to add. In 2015 Toby told us that It was Raining Somewhere Else. Ten years later he showed us where.

In Undertale this song is directly related to UT Sans' relationship with UT Toriel, and how this friendship is the reason he helps us throught the Underworld. In Deltarune, however, this songs plays after we leave the Church at the end of Chapter 4, on the way home. Nevertheless, it's back home that we learn of the friendship DR and DR Toriel have.

Not only the titles, not only the melodies –althought in Deltarune it sounds distant, almost like an old memory brought back by the smell of the rain–, but the context of these two songs connects them between games. Moreover, a slowed down version of the song can be heard at UT Sans' Secret Lab, as if the "Don't Forget" message inside it wasn't enough of a giveaway.

3.3 Non-musical clues:

How the Player interacts with the world seems to also imply a connection between games. Specially those lines that point to the Player knowing characters –or things about characters– that Kris doesn't know yet. For example, the first time we meet DT Sans there's the option to tell him that we're happy to see him again, something that makes sense for a Player that has already played Undertale, but doesn't for two characters who just met, as Sans points out.

This in and of itself is not enough to prove that the games are both a direct sequel and prequel of each other but, in combination with everything else, it heavily add to that idea.

Besides these interactions, which could be taken just as silly easter eggs, like the annoying dog appearances, there's another non-musical clue which brings us back to UT Sans: the Warp Doors, which look just like UT Sans' bedroom door, fire animation and all. What's more, Mystery Man's door in Undertale uses the same sprite as well.

I'm certain that Undertale's Underworld is not a Dark World, since there are no Dark Fountain to be found, nor darkners, the style of the menu is the same as in Deltarune's Light World, and to break The Barrier you need 7 souls, not just one. This complicates things, for the Warp Doors only appear inside Dark Worlds in Deltarune. But then again, in Deltarune, monsters seem to only possess magic powers inside Dark Worlds, while in Undertale all of them have this gift.

4 The Delta Rune:

Both the appearance of the Delta Rune in the two games and its name are big indicators of the connection between games. Even though in Undertale it’s not well known what its original meaning was, there’s a prophecy that sounds remarkably alike to that of the Delta Rune Legend from Deltarune. In Undertale there are two interpretations: either the Angel will murder all monsters, or free them all from the Underground. Additionally, in Deltarune, the Legend Ralsei tells us says that the Angel is to be defeated by three heroes: two lightners -a human and a monster- and a darkner.

Since the Delta Rune is older than written history in Undertale and it’s original meaning was lost to time, that one of the 2 interpretations for this symbol is so close to the Legend Ralsei gives us, with an evil Angel instead of a benevolent one, could mean that, originally, both Runes had the same meaning behind.

5 Blood & Magic:

Back in 2022 this part of the post began with:

TL;DR: As always, blood seems to be the biggest issue around Sans’ theories. To summarize, unless we get undeniable proof that DR monsters do bleed in some way before turning into dust, UT Sans bleeding could be a huge weak point for this theory.

Welp. We got it. Susie bled.

It’s fair to say that UT Sans does bleed in Undertale's Genocide Route, before turning into dust outside the screen. And he’s the only Undertale monster that does. We know he bleeds because he does it from the mouth, as well as the ribs, far from where the Player cuts him, which would only happen with regular bleeding around a digestive system rather than with ketchup stored within his rib cage.

Three years ago this was a huge nuisance, but now, knowing that a Deltarune monster can and does bleed, it' becomes another huge piece of evidence for this theory.

However, there's an issue. At the end of Chapter 1 a monster –not The Monster Kid– asks Kris if it hurts to be made out of blood, implying that other monsters don't bleed. This looks to be in direct contradiction to what we see Susie say (i.e. "Everybody bleeds") and do. As of now, I've no idea how to explain this line of dialogue.

5.1 Magic:

Deltarune monsters having magic powers is a highly debated topic. Nevertheless, Sans does teleport in Chapter 4, appearing both at his shop and at the Cattenheimer's home. Furthermore, it's implied that Catti holds some magical powers, which makes it all the more interesting that Sans teleports to her front yard.

6 Conclusions:

With all this in mind, I’m quite sure that, at the end of Deltarune, Sans will end up being stuck in the Undertale universe, possibly using the machine he keeps covered up in his lab. Since Papyrus doesn’t seem to be much different to any other monster in the Underground I don’t think he comes from Deltarune’s universe, so I fear a tragic end for that Papyrus, specially after his dissappearance after Chapter 3.

This ending would make sense of the whole ”Your choices don’t matter” thing. The Weird Route seemed to contradict this statement but, if just Sans is going to Undertale, whatever you do on Deltarune’s Universe won’t matter to Sans’ end. Undertale’s story is already written and the end we got will remain untouched, as Toby said. It also implies that our actions don't matter to Deltarune's end either.

We now know that the End of the Prophecy is a tragic one, as evidenced by Ralsei being terrified of what's to come, and Susie being enraged and in denial. A tragic end would also align with Sans' depression in Undertale, and him being the only one to come from Deltarnue's universe.

But, if Deltarune is a prequel, how is it that the Player recognizes the characters that both games have in common, and it’s advised that the game is played after Undertale? I believe that Deltarune is a prequel from Sans’ perspective, and a spiritual sequel from the Player’s. The Player, being the meta-being that it is in both games, doesn’t need to abide by the same temporal rules the characters are forced to follow. Thus, there's no contradiction in Deltarune being a prequel to Undertale. A Pre-Sequel.

7 Problems with this theory:

UT Papyrus seems to not know anything about his brother’s possible past in another universe, and acts as if they had been together since forever. They both appeared one day in Snowdin and his past seems as mysterious as Sans’, but they can’t be directly related since Papyrus doesn’t bleed.

There's a contradiction between Susie bleeding and the monster kid asking Krist if it hurts to be made out of blood.

I don’t know how will Sans get to Undertale’s world (my guess is Gaster, but he’s a bit of an easy-way-out in theory crafting).

Grillby’s. Sans’ convenience store, ’Sans, appears to have the same façade as Grillby’s in Undertale, with the name of Grillby rubbed off. This small detail is a possible proof against the sequel thesis, albeit it could just mean that Hometown had a Grillby’s before Sans’ convenience store and it closed down for some unknown reason.

Although some problems still remain, the list of issues with this theory has been greatly reduced after playing chapters 3 and 4. Furthermore, we now have great new pieces of evidence that point directly towards a connection between games.

[mystii-gur0]

Guys it took ten years but I think I finally figured out who Gaster is

So I was talking to my friend in DMs yesterday about Undertale and I was telling him about how we basically know nothing about Gaster besides that he was the Royal Scientist before Alphys, potentially made Sans's blaster, and was shattered across time in space after falling into his own creation, which we assume was probably the Core. And also how we suspect he's a skeleton because his name is W.D. Gaster (being likely a combination of the fonts Wing Dings and Aster) and the so far the only characters that are named after fonts and speak with a font/typing quirk are obviously Sans and Papyrus, who are obviously skeletons.

So then I was like "haha, what if Sans is Gaster cause they're both sciency and skeletons" as like a joke. And then I started to think about it.

My initial theory was that Sans is just straight up Gaster and the "falling into his own creation and being shattered across time and space" thing was just a metaphor for Sans loosing his shit over figuring out the whole other time lines thing, but that theory had well- a lot of holes, to be nice to myself. For one thing, Sans and Alphys are friends. And if Sans was just straight up Gaster, one would think Alphys would recognize him and be like- "Dude didn't you use to be my boss?" Or smth. And not just Alphys, if Sans was Gaster I would think more people would recognize him. And that doesn't solve and of the weird stuff about Papyrus either. Given that he and Sans BOTH just kinda showed up one day, according to the shop keeper in Snowdin.

But I liked this theory, so I kept thinking, and came to what can only be described as an epiphany or my very own eurika moment.

Sans and Papyrus are BOTH Gaster.

CAUSE THINK ABOUT OK

IT ANSWERS EVERYTHING

Gaster was shattered across time and space after falling into what we assume is the Core. Key word, SHATTERED, as in split into peices. Sans and Papyrus randomly show up one day with little to no explanation of who they are or where they came from? ANSWERED BY THEM BEING WHAT'S PHYSICALLY LEFT OF GASTER IN THEIR REALITY. THEY DID NOT EXIST UNTIL GASTER FELL INTO THE CORE. Sans (and probably Papyrus) using Gaster blasters? ANSWERED BY THEM BEING GASTER. OF COURSE THEY WOULD USE GASTER'S ATTACKS IF THEY WERE GASTER. Sans being significantly physically weaker and smaller than Papyrus, all though he's better with people and scientific concepts? ANSWERED BY THEM BEING UNEVENLY SPLIT. Sans and Papyrus having drastically different personalities, typing styles, and character designs that could almost be described as exact complementary opposites? ANSWERED BY THEM BEING PARTS OF A WHOLE PERSON. Sans only having one glowing eye that's conveniently the same eye that what we assume is the Gaster overworld sprite has open? ANSWERED BY HIM BEING A PEICE OF GASTER.

"Oh but Sans and Papyrus are brothers!" What other word would they have to describe what they are? They're like brothers by mitosis or smth 😭

I'm loosing my marbles i need a cork board with string

Edit: actually now that I'm thinking about it, their codepency makes a lot of sense if you look at them this way. They just want to be whole again @_@

[kitteninatux]

Something I really think people fail to consider for Post-Game Undertale is how the value of gold fluctuates

Since using G (gold) to make transactions is traditional for the economy of the underground. How would the humans react to the sudden influx of such an expensive and precious metal- what would happen to at the very least- the local economy? It’s already a given that Monsters would be able to adapt and improve the work on certain careers (ex: Grillby being a fire elemental monster can give him an advantage with cooking- due to his first hand knowledge of it.)

But what would that all entail for the humans in the area surrounding Mt. Ebott? There would certainly be a struggle on pricing the new value of gold after they all found out there was an entire underground supply of it. In my personal opinion, I think the most canon bet to it (assuming from the end credits) would be that Monsters are all conveniently rich and treated with confidentiality.

Kind of like

“Hey! If you give us all that gold you gathered and used in the underground, then we’ll trade ya some property and housing arrangements!”

Because Toby fox would absolutely pull some fourth wall breaking jokes with that. And Temmie would somehow make us cry over how majestic it was.

With that logic it’s also funny to imagine a scenario where either Genocide Frisk or Asgore slaying Frisk comes up to the surface ridiculously rich.

Just a random eight year old in a striped shirt waltzing down from a certain death distance and proudly displaying all the weirdly dusty pure gold trophies they got

[simonsoys]

Do you think papyrus is a good liar or that he can keep a secret? I remember him using reverse psychology on undyne once but his lie to impress undyne was a bit obvious

(such a hard character to fit into a theory - because he doesn’t know what the sun is + remembers green grass before snowdin, but I’m still trying to figure out that mysterious skeleton!)

Well 100% he's a liar. See below:

It seems to me he's a great liar in most conditions. He definitely knows what the sun is, and he even references it when he's talking to you privately. It's only at the end when he's standing next to Sans and the other characters that he pretends not to know what the sun is. In the King Papryus ending he literally waits until Sans has left to break down and complain about the job.

He lies about how clueless he is in front of Sans A LOT. Like A LOT A LOT.

In the grease example, I think he's doing a worse job because he's quickly back-tracking. IIRC he says he hates grease, Undyne says she likes Grillby's, and now he doesn't want Undyne to think he's uncool so he fibs and changes his mind.

There must be something very important about lying to Sans, because he does it so flawlessly compared to things like fibbing to Undyne.

[forgettable-au]

What was your inspiration for the story? Where did you learn about the theory to begin with?

I'VE TALKED ABOUT THIS BEFORE, BUT SOME OF YOU MIGHT NOT KNOW

BUT JUST SO YOU ALL KNOW

IT ALL STARTED HERE:

I don't like taking credit for the Papyrus is Gaster concept because

I DID NOT COME UP WITH IT, I FOUND OUT ABOUT THIS THEORY BECAUSE OF THIS COMIC

WHICH I STILL LOVE VERY MUCH

It changed my brain chemistry I think

I was just watching Undertale comic dubs as normal and I stumbled upon this one

I was a little confused because... why does Gaster look so much like Papyrus?? AND THEN I REALIZED

AND FOR SOME REASON I GOT OBSESSED WITH THE IDEA

Only to find out the comic was abandoned...It was rough...

So, I started to develop my own AU using that concept!

I am going in a VERY different direction with my comic but it is still pretty clear that I took inspiration from this comic

The IKTIKN comic belongs to linssins! If it wasn't for that comic I wouldn't have found out about this theory, so I will never stop mentioning it