Gaster Undertale Guide

Gaster Undertale Guide

Of all the mysteries in Undertale, the most prevalent one with minor information is that of W. D. Gaster. Everyone who took part in the discussion around Undertale in 2016 probably has a vague idea of him, but not everything in concrete detail. The issue is that there isn’t too much factual information around him.

Undertale has a few events that speak about him, his legacy, and his existence, and Deltarune has a few examples of who he is now and what he might be doing. Still, we really can only speculate after connecting all the dots. So in this Gaster Undertale guide, I’ll provide our info, combine it into the story we know of Gaster, and speculate just a little.

gaster undertale
Image from Undertale Fandom Wiki

Bottom Line Up-Front

Gaster is a secret character with information about him only found incredibly randomly throughout Undertale. He was the royal scientist before Alphys and most likely the person who created the world of Deltarune. There are tons of hints that he could end up being fully elaborated on in Deltarune due to a large number of suggestions towards him in that game.

Undertale: Shape Your Destiny Beneath the Surface | GOG

Embark on an unforgettable journey through the underground world of Undertale, where every choice you make shapes the fate of monsters and humans alike. With its charming retro graphics and innovative gameplay mechanics, immerse yourself in a tale of friendship, determination, and the power of mercy.

Check Price Buy at GOG
We earn a commission if you make a purchase, at no additional cost to you.

Who Was W. D. Gaster?

Well, for a start, W. D. Gaster likely stands for Wing Dings and Aster, both being fonts. The fonts Gaster uses during certain logs or events are always the font Wing Dings. Aster is derived from the name Gaster and the theme of naming characters after fonts. We can imply from this nature that he is a skeleton, like Sans and Papyrus.

Gaster’s Followers

When you have a specific “fun” value randomly picked between 1 and 100 every reset, you can find specific events that almost always relate directly to Gaster. For example, the most direct lore drops happen around fun values 61-63, where a random follower of the scientist appears in Hotland.

These events are improbable, so much so that I couldn’t replicate them through save file editing. So instead, their dialogue is a cryptic backstory on Gaster’s story, and how he ended up in the state he’s in. The first followers’ dialogue is as so:

“It makes sense why ASGORE took so long to hire a new Royal Scientist. After all, the old one… Doctor Gaster. What an act to follow! They say he created the CORE. However, his life… was cut short. One day, he fell into his creation, and…Will Alphys end up the same way?”

From this, we can tell that Gaster was the original Royal Scientist; there was a large gap between him and Alphys. He made the core and fell into “his creation,” which likely means the CORE, but because of the way the dialogue is worded, we can’t say for sure. The second follower’s dialogue is framed like a riddle, like so:

Image from Undertale Fandom Wiki

“Alphys might work faster. But the old Royal Scientist, Doctor W.D. Gaster? One day, he vanished without a trace. They say he shattered across time and space. Ha Ha… how can I say so without fear? I’m holding a piece of him right here.”

This implies Gaster was a particular and slow-moving scientist, working on more intricate and massive projects than Alphys. He was shattered and split across time and space, and a piece of him ended up in this follower’s hands. If we believe the CORE is what he fell into, then the large amounts of magic and geothermal energy stored within might have been the cause for his shattering. The third follower’s dialogue goes like this:

“I understand why ASGORE waited so long to hire a new royal scientist. The previous one… Dr. Gaster. His brilliance was irreplaceable. However, his life… was cut short. One day, his experiments went wrong, and… Well, I needn’t gossip. After all, it’s rude to talk about someone who’s listening.”

Once again, confirming the genius and irreplaceable mind that was W. D. Gaster, we also learn that his falling into his creation resulted from a failed experiment. However, we also understand that he’s listening to this conversation somehow as if he’s some omnipresent force constantly around.

Other “Fun” Events

Each event correlating to the “Fun” value has some relation or thread with it and Gaster, either by directly hinting at him or having some correlation to the events of Deltarune, which I’ll get to a little bit later in this guide.

Mystery Man

undertale door

If your fun value is exactly 66 and you enter the room between the cheese with the save point, and sans’ telescope in Waterfall, you may come across this door. Unfortunately, it only has a 10% chance to appear, so you may have to edit your save file and reload a lot to see it.

undertale mystery man

You’ll see this figure by entering the door, which is only ever referred to in the files as “mystery_man.” Interacting with him will make him get scared and disappear, with no dialogue or anything. Likewise, if you leave this hallway, it disappears forever.

This is the look you’ll often see people portraying Gaster with, and while I think it’s the most likely candidate for his appearance, there is absolutely nothing confirming this. He does look like a skeleton that’s been warped or shattered somehow, though, so the connection is clear.

Goner Kid

goner kid undertale

Goner Kid shares a resemblance to both the Gaster followers and Monster Kid. However, he will only appear at the end of the dock where Undyne threw spears at you if your fun value is 90 or higher. And he has this to say:

“Have you ever thought about a world where everything is exactly the same… Except you don’t exist? Everything functions perfectly without you… Ha, ha… The thought terrifies me…”

If you’re holding an umbrella, it’s this:

“An umbrella…? But it’s not raining. Ha, ha… You know, that does make me feel a little better about this. Thank you. Please forget about me.”

These sound like the doubts and regrets of one W. D. Gaster. He can see the world still running just fine after he got fractured across time and space. However, he no longer exists, at least not wholly, and wants to share these thoughts with the protagonist through this surrogate.

Sound Test

Another one I had a large amount of trouble getting to trigger in-game is the Sound Test. It only plays when heading up from the box room in Snowdin after defeating Papyrus with a fun value of 65. Even though I had all these, the game never wanted to let me in.

You can scroll over to the one called “Gaster’s Theme,” It will prevent you from doing anything other than listening to the entire thing. After you’re done listening, you get some text saying, “Thanks for your feedback! Be seeing you soon!” and get booted out to the fishing room.

You can find it here if you want to listen to Gaster’s theme. It’s an incredibly short melody, which some might claim has leitmotifs throughout Undertale and Deltarune. However, it is just a super simple melody, so they may just be hearing things where there isn’t anything.

Phone Calls

wrong number song
Image from Undertale Fandom Wiki

Now we’re getting into things that are less directly related to Gaster but all part of fun value events, so they’re likely at least meant to be interpreted as some relation or pointer to being about him.

In Snowdin, once again at the box room, going up when your fun value is 2-39 (which means you might have gotten this one usually with no save file editing), you’ll get someone calling the wrong number, asking for a “G…” Obviously, this could be Gaster, or it could be Grillby, Gerson, or some other character who’s name starts with a G, you never really know.

If your fun value is between 40 and 45, you might get a call from Sans in Snowdin, and if it is between 46 and 50, you might get a call from Alphys in Snowdin. These are both jokes, with Sans prank calling you and Alphys trying to order a pizza, but these two characters are especially relevant to Gaster. Alphys for being the royal scientist, and Sans for many reasons I’ll go over later in this guide.

monster kids word search
Image from Undertale Fandom Wiki

Possibly the hardest one to relate to Gaster, if you get a fun value from 56-57, you’ll have an additional character on the word search Papyrus gives you; this one is “Nightmare.”

Nothing about this is explicitly related to the old royal scientist. Still, Ice-E’s character became far more prevalent in Deltarune, as well as the word skeletons appearing on the word search.

Clam Girl

clam girl
Image from Undertale Fandom Wiki

If you have a fun value between 80-89 and are on a pacifist or neutral route, you may come across this Clam Girl character in Waterfall. This one is especially curious since she usually doesn’t appear at all. Her dialogue goes like this:

“I’m visiting Waterfall from the city. Synchronicity…? My neighbor’s daughter looks about your age. Her name is “Suzy.” I feel like you two should be friends. You have… A neighbor’s blessing!!! Not knowing where I live is no issue. Fate finds a way. In life’s grand scheme, she might be why you came here in the first place…”

If you kill Undyne and then meet the Clam Girl, you get this dialogue:

“I sense a disturbance in the nearby aura… I think you should leave that girl alone.”

After beating the game, you get this dialogue:

“So you never met my neighbor’s daughter. Don’t despair. This world has infinite opportunities. But there’s a limit to the things you can do today. Accepting this is healthy. Take my neighbor’s blessing! And consider this blessing for anything you like!”

If you beat the game and then talk to her after walking by her in the first place, you get this dialogue:

“I wanted to tell you about my neighbor’s daughter. But you walked right by me before I could tell you. Fate has decided that I should not tell you.”

Suppose you specifically beat the game on the Nintendo Switch and talk to her. She will say the most exciting dialogue after turning to a greyscale color scheme, like the goner and Gaster followers.

“So you never met my neighbor’s daughter. But please don’t despair. Because the time that you will meet her… … is fast approaching.”

After this, she disappears, with the same sound effect used when the Mystery Man disappears. The most striking part about this is that chapter 1 of Deltarune was released shortly after the Switch release of Undertale.

This heavily implies the Suzy she was talking about was referring to the Susie we see in Deltarune. Given we know Toby Fox has been working on Deltarune long before Undertale, it isn’t a stretch to say he planned this connection from the start.

Given her grayscale appearance, her sound when disappearing, and the immense foresight leading into a game that loves connecting itself to Gaster, we can assume she was given some piece of Gaster and given the foresight to know about his next project.

Unused Files

There are many unused things left in the files that all contribute to the mystery of Gaster. Please take all of these with a grain of salt; none of them can show up in any version of Undertale and may or may not be foreshadowing or information to take seriously. For all we know, this was discarded on purpose and is never to be brought up again.

Entry Number 17

room 264
Image from Undertale Fandom Wiki

The only one I cannot see being confirmed as non-canon, Entry Number 17, would be accessed in the same place all the other log entries are, in the True Lab underneath Alphys’ house.

This one is written entirely in uppercase wingdings, giving us a feel for how Gaster writes. The entry goes like this when translated:


This same style of writing comes back at the start of Deltarune and a few other times to indicate that it is Gaster speaking. The “Dark, Darker, Yet Darker” part of it, specifically, has become a catchphrase of his.

The “You Two” at the end of the message can refer to various characters. Still, the part about growing darkness and negative photon readings is almost certainly related to Deltarune and the dark fountains in that game.

Room 272

room 272 location
Image from Undertale Fandom Wiki

One of the strangest cut rooms in Undertale contains a mysterious figure referred to in the files as “redacted.” As you walk up to him, he starts fading out; interacting with him gives you the message “REDACTED” in wingdings.

The wingdings do seem to indicate this is Gaster. Still, I think the super unpolished and unfinished look of this room and the simplicity of the message means this might be a scrapped version of the mystery man’s room and not much else.

Leaving this room takes you to the sound test room, where you can again listen to Gaster’s theme.

Room 123

room 123 location
Image from Undertale Fandom Wiki

In another room that looks super unfinished, there’s an NPC you can talk to in the middle that will say there’s a man with a creepy smile behind you, and if you turn around, he disappears.

No sprites were implemented in this, so we can only assume that it might be Gaster, but it could also be Flowey or Sans—nothing concrete here, but maybe another Gaster reference.

References to Gaster in the Normal Game

Regardless of fun values, cut content, or what have you, some references to the past Royal Scientist are blatantly within Undertale; no save file editing or room warping is required.

The Man Who Speaks in Hands

Image from Undertale Fandom Wiki

Sometimes when using the fast travel boat in Undertale, the River Person will say, “Beware of the man who speaks in hands.” Due to Gaster’s nature of only ever talking in Wingdings, it is assumed that is who he refers to.

He can also say, “Beware of the man who came from the other world.” This one is less clear since we have no clue if Gaster originated in the world of Undertale or if he came from a different universe or reality altogether.

The River Person is generally cryptic, but this does give us a strong warning. If we ever met Gaster, at least if he were entirely pieced together in this reality, he would be a force to be reckoned with.


papyrus and sans's house location

Sans has a few connections to Gaster outside of just being a skeleton. The workshop behind his house has a strange machine under a curtain, blueprints in handwriting that are entirely indecipherable, a badge, and a poorly drawn picture of 3 people with “don’t forget” written on it.

These can all be interpreted as references to Gaster, the machine might be Sans working on something to bring him back, the handwriting could be in wingdings, the badge might be a badge from working at the lab, and the photo is an apparent reference to Deltarune. The trio of protagonists and “don’t forget” is the game’s central theme.

Also, during the fight with Sans, the weapons he uses are called “Gaster Blaster” in the files, implying he inherited or acquired them from Gaster. Plus, while this isn’t in the game itself, on the official Undertale Tumblr, Sans gives an in-character post that says, “besides, it’s rude to talk about people that are listening, right?” Just like the Gaster follower before.


The final thing to consider is that naming the character Gaster in either Undertale or Deltarune will reset the game to the start. This means that there is definitely something up with Gaster’s omniscient, god-like behavior if he can reset the game similarly to Flowey.

That said, there’s still more info to gain from checking out Deltarune’s information on the man who speaks in hands. While Undertale and Deltarune aren’t necessarily related, Deltarune takes many events, ideas, and especially characters from Undertale, and things in one game can affect the other.

Deltarune Gaster References

Luckily, dealing with Gaster in Deltarune is much easier since none of the references to him have anything to do with fun values, cut rooms, or the like. Nevertheless, Gaster is connected to Deltarune in some way; even the way Deltarune was first introduced makes this clear.


deltarune gaster twitter

In October 2018, a Twitter takeover occurred on the official Undertale Twitter account. The name changed to 6 black boxes (with Gaster being six letters), and many cryptic tweets with odd spacing and in all caps were sent out. After these tweets, a link to was sent, and chapter 1 of Deltarune was released.

Potentially the strangest reveal of a video game ever (but it’s Toby Fox, so what did you expect). This event set the entire community on fire because we are all almost entirely sure this was Gaster himself speaking in the same style as entry number 17. Almost definitely confirming the entry as complete canon, too.

Gaster acknowledges the community’s active hunt to track him down and any traces of him and wants to show us something very, very interesting. He wants answers for an incomplete survey, and he’ll contact us again soon. When we got our hands on Deltarune, it opened with a survey, and an omniscient presence speaking in all caps, with weird spacing.

gaster tweets

gaster tweets 2

On the release of Deltarune Chapter 2, on the 17th, no less, another set of cryptic tweets got sent out. I especially appreciate the 2nd and 3rd tweets acknowledging the “difficult times” of the three years between releases. But, unfortunately, even being shattered across time and space can’t free you from covid.

Most of this is just more cryptic messaging with little sense or meaning in the style of Gaster, but the second connection does reference the second dark portal getting opened. I wish there were more lore drops for this, but we can only speculate what this second batch means.

Survey Program

survey deltarune

At the very opening of Deltarune, you’ll get an incredibly strange first experience, with text remarkably reminiscent of entry number 17 when translated from wingdings. This character creator establishes a connection with you and lets you create a character.

Once you’ve picked your head, torso, and legs, it says you have created a wonderful form and gives you a survey. All this is done over a clear rendition of Gaster’s theme as heard in Undertale, just missing a note. The voice always says “we” instead of I or you, which is mildly unnerving.

After creating the character, a different font tells us our creation will now be discarded and that no one can choose who they are in this world. We don’t know who this other voice is, but we do know that the lack of freedom is a common theme in Deltarune.

None of this has come up again as of Chapter 2, but the files for the character you create reference them as a “goner,” like the kid we saw in Undertale. We can be almost entirely sure this voice is Gaster, there’s very little pointing to the contrary other than him not speaking in wingdings, but I think making the seizure warning unreadable would have probably been bad.

Optional Bosses

spamton neo battle idle
Image from Deltarune Fandom Wiki

Both the optional bosses, Spamton and Jevil, have implied connections to Gaster.

For Jevil, Seam, the shopkeeper, mentions he went insane after meeting a “strange someone” and used to be a regular court jester before then, having to get locked away in the castle basement after this particular person drove him to madness.

For Spamton, there’s an even more direct connection. Using your phone anywhere in the dark world will cause the same audio to play as in entry 17, with the description being “It’s just garbage noise.” For example, after defeating Spamton, one of the Addisons in the garbage dump will say he talked to a man who changed his life and gave him success but one day cut him off. They went to check on him, and the phone was hanging off the receiver, and when they went to check, it was “just garbage noise.”

Connections like these aren’t coincidences. Toby usually words things in particular ways to correlate or imply things, and with only two things in the game being called garbage noise, we can be pretty sure this is a direct connection to Gaster. I firmly believe that all the future optional bosses in Deltarune will all be driven insane by Gaster.

The Man with the Eggs

gaster egg

Bit of a weird one. In chapter one, you can go between a room transition and find a hidden room with a man behind a tree who will give you an egg for interacting with it. The text says “he” is behind it, which is reminiscent of the character creation track being called “another him,” and a few other times Gaster is referred to as “him.”

We can find the man in the cars at the beginning of Chapter 2, waving at us happily. In the tree room of Cyber City, you can reencounter him, being given an egg. After interacting with him, inspecting the tree will say, “there was not a man here.”

These occurrences with a seemingly non-existent man are all too strange not to be at least somewhat related to Gaster.


Image from Deltarune Fandom Wiki

The last piece of information I want to cover in Deltarune is the shopkeeper, Seam, saying Gaster’s classic line. If you talk to him about Jevil, he has this to say:

“Since that time, the strange words he’s said have stuck inside my cotton… And my view of this world has become darker, yet darker.”

Darker, yet darker, the fact that Seam specifically knows this despite not having much of any interaction with Gaster is strange, but it is no doubt a direct reference to him. I wouldn’t be surprised if we happened to hear more about the shopkeeper meeting with the scientist in later chapters.

How to Fight Gaster

From Pingas2000 on Gamejolt

To put it bluntly, you can’t. Quite a few fan mods, animations, and ideas depict a fight with the royal scientist. Still, there isn’t anything in any official Undertale or Deltarune media that so much as visually represents him, much less allows you to fight him.

This picture is from a fangame made by Pingas2000 on Gamejolt, and while I’ve seen this picture tossed around the internet a ton, it isn’t canon. Certainly a cool fangame, though; the boss itself is a bit slow, but still a neat fight. And hey, maybe we might end up fighting him in Deltarune one day.

Questions and Answers

Question: Who is Gaster in Undertale and Deltarune?

Answer: Gaster was the royal scientist before Alphys, before getting split across time and space.

Question: Why should I care about Gaster for Deltarune?

Answer: Gaster is critical to the plot of Deltarune, having been the one who made the tweets revealing the game and the one in the introduction of the game speaking to you.


W. D. Gaster is a name I heard crop up many times during the peak Undertale craze on the internet. Being a part of the fandom and discourse around the game for quite a while, I got incredibly frustrated just not knowing hardly anything about this mad scientist who seemed both omniscient and inherently intelligent.

Having seen the references to Gaster in Deltarune, I can appreciate all the mystery surrounding Gaster and who he was. Each breadcrumb of info is just the right amount of spice, telling you barely less than what you want to know, making you yearn for more. I cannot wait to see more info on Gaster in Deltarune.

Undertale: Shape Your Destiny Beneath the Surface | GOG

Embark on an unforgettable journey through the underground world of Undertale, where every choice you make shapes the fate of monsters and humans alike. With its charming retro graphics and innovative gameplay mechanics, immerse yourself in a tale of friendship, determination, and the power of mercy.

Check Price Buy at GOG
We earn a commission if you make a purchase, at no additional cost to you.
Latest posts by Monica Phillips (see all)

Leave a Comment

Your email address will not be published. Required fields are marked *

Scroll to Top