NOTE: Please read the whole thing before making a comment.

So, those of you who have beaten the game through and through are probably wondering to yourself, who is this Gaster guy people are talking about?

It seems that this game's secrets lie much deeper than you'd think.

This guide is a work in progress, and will frequently be updated when more information on Gaster arrives. If you have any information regarding Gaster, please leave it in the comments of this guide.

Collaborative Google Document:
https://docs.google.com/document/d/1h_vdEFZMtefD-nkCZ7ODzArp7BRbGgN0_7HQ1XjTT8Y/edit
Because we CAN have nice things, someone has kindly made another one before this one got nuked off the face of the earth. Please don't trash this one. Special thanks to Djin:
https://docs.google.com/document/d/19uzqacgnuRgNce8U2xcQRXI3AGCBAAairr_zz9N00Hk/edit
Third time's the charm. Thanks to squidvillager for this one.
https://docs.google.com/document/d/1-MkE0cs2l8R_bcQe1s6LLk0GR3DFFGYmMg45hGhTSqo/edit?usp=sharing

Sometimes when you meet the Boat Lady, she'll say to "Beware of The Man who Speaks in Hands." This seems odd and out of place, until you manage to find...

At the moment, we believe these occur when you capitalise your 'fun' value in the game's files, and change it to either 63 for the head, 62 for the guy on L3 and 61 for the Donut Guy.

https://d.maxfile.ro/hezbgyxqgq.webm

By 'The Man who Speaks in Hands', we can only assume that the Boat Lady is talking about this guy, or Gaster. What was the bizarre noise he made when he disappears? This only creates more questions, and more mystery.

It's very possible that Gaster could be the item in the Donut guy's hands that appears to be speaking, but it's also worth noting that this could mean something else...


The Grey Kid is, from what we can assume Gaster talking through the boy. A world where he doesn't exist pointing to Gaster's current existence, a being shattered through time and space.

You can also take an umbrella to him, triggering different dialog. He soon prompts you to 'forget about him'.


The third gif, containing the grey person (whose name I cannot remember, I swear I've seen him before) talks about how Gaster fell into the core, his 'own creation', cutting his life short. We can only assume this is what caused Gaster to shatter across time and space itself.


The fourth, containing the bizarre grey face, mentions that his life was cut short due to an experiment going wrong, before saying that it's rude to talk about someone while they're listening.

Perhaps there is some secret way to access the core? Seems very likely seeing as quite a few of these appear by the elevators near the core.

Thank you to ropnolc of getting a video of this.

NOTE: Receiving this call appears to be potluck, and we're not sure at all what causes this to happen.

Going to the riverman before going to Papyrus can cause this to occur, in which someone calls asking for 'G...' before stopping and realising that it's a wrong number he's calling, before a small ditty plays. The implications of you recieving this call are currently unknown.

Perhaps one of the more curious secrets, naming yourself 'Gaster' on the file select will send you back to the intro video. We are currently unsure if this changes anything.

While having your 'fun' set to 'Fun' and having a value of 65, you can get a sound test to appear.

https://d.maxfile.ro/fqwkvlcmyj.webm

Perhaps the most curious thing about this sound test are, aside from the lack of any of the game's actual music, the other songs included within, 'Happy Town', 'Meat Factory', and 'Trouble Dingle'. What are these short loops of music, and what are they supposed to mean?

Gaster's theme itself is bone-chilling enough. We still are unsure of what this could mean, or how we are supposed to use this.


That being said, putting Trouble Dingle into an Audio sounder shows that the notes make an arrow shape. Very curious indeed.

https://d.maxfile.ro/beryidzssq.webm

By changing your room number in both your save0 and your .ini file to 264, a set of wingdings will appear. This is what happens when you load a save. The Wingdings written translate to:

"ENTRY NUMBER SEVENTEEN

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?"

You two? Could this potentially be referring to Papyrus and Sans? Toriel and Asgore? The player and someone else? At least we can finally know what the seventeenth entry in the True Lab actually says.

The wingdings themselves could also be another nod to 'The Man who Speaks in Hands', as there are a few hand symbols that replace some letters in the font itself.

Sans himself has a lot to do with this.

Straight from the game's data, take a look...

\E1* wait a second./
\E1* that look on your& face while i was& talking.../
\E2* you've already heard& my spiel^1, haven't you?/
\E3* i suspected something& like this./
\E3* you're always acting& like you know what's& going to happen./
\E1* like you've seen it& all before./
\E3* so..^1.&* i have a request for& you./
\W*\E1 i kind of have a& \Ysecret codeword\W & that only i know./
\E0* so i know if someone& tells it to me.../
\E1* they'll have to be a& time traveller./
\E2* crazy^1, right?/
\E1* anyway^1, here it is.../
\E3* (whisper^1, whisper)/
\E2* i'm counting on you to& come back here and& tell me that./
\E1* see you later./%%
\E1* huh^1?&* do you have something& to say to me?/
\E2* what^1? a codeword^1?&* can you speak a& little louder?/
* did you.../
\E2* ... just say "i'm a& stupid doodoo butt?"/
\E1* wow^1.&* i can't believe you& would say that./
\E3* not only is that& completely infantile.../
\E2* but it's also my& secret codeword./
\E3* that^1, however^1, isn't& good enough./
\W*\E1 what you need is the& \Ysecret\W secret codeword./
\E2* it's only for people& that know the secret& codeword./
\E0* anyway^1, here it is.../
\E4* (whimsper^1, whimsper).../
\E2* ... just say "i'm the& legendary fartmaster?"/
\E1* wow./
\E1* that's..^1. uh..^1.&* really childish./
\E2* why would you think& that was a secret& secret codeword?/
\E1* whoever told you that& is a dirty liar./
\E2* i don't have a secret& secret codeword./
\E3* however./
\E2* i do have a secret& secret triple-secret& codeword./
\E1* which you just said./
\E2* so^1, i guess you're& qualified./
\E2* here's the key to my& room./
\E3* it's time.../
* you learned the truth./
* (When you looked^1, the key was& already on your keychain.)/%%
\E1* huh^1?&* triple secret codeword?/
\E2* nah^1, i'm out of& material./
* (You felt something on your& keychain.)/%%
sansf
sansk
\E0* heya./

To gain access to Sans' secret Workshop, you need to be at the end of a True Pacifist run, before the final corridor where Sans gives your lecture. Let Sans explain EXP and Love to you and then reload your save repeatedly. He'll recognise your time travelling powers and give you a key to his room. Once you've entered his room, walk around and trigger a cutscene. Once you're done with this, check Sans' drawers and you'll find a Silver Key. Once you've done this, go behind the left side of their house and you'll find a door that you can unlock. Inside will be some kind of Machine behind a curtain, as well as some drawers filled with blueprints and one containing 'A photograph of you and Sans with all your friends, and Sans with some other people you don't recognise.' The blueprints are written in what the game refers to 'Strange Symbols. Or it could just be the handwriting.' This could potentially poke at Gaster having built the strange machine, and the 'Strange Symbols' being Wingdings.

Thank you to Meido Grempy for recording the footage.

People have theorised that this machine behind the curtains is some kind of Time Machine, which would perhaps explain Sans' ability to warp around at random (Doggo claims he doesn't like Sans because he travels without moving). It's also worth noting that during the Genocide run with Sans, he talks about how he's been monitoring the timelines for anomalies, and also mentions an 'Us'. This further deepens his potential connection to Gaster.

We have indeed found the method to access this bizarre creature that we can only presume is Gaster.

By setting your fun value to 66 (making sure it's capitalised), this door may appear.The fact that the door just mysteriously appears out of nowhere brings up many questions.

One of the ferryman's messages is 'Beware of the man from the Other World'. Could this door be the other world they're talking about?

People have pointed out that the W.D part of his name could refer to Wing Dings, as that is what Gaster presumably speaks in.

As Gaster speaks in wingdings, he speaks in a font like the other skeletons do, further solidifying his association with Sans. But, Gaster isn't the name of a font.

Not until you think of it this way...

W.D Gaster
Wing Din Gaster
Wing Ding Aster

Aster itself IS a font, and as well as that, a genus of Flower.

http://undertale.tumblr.com/post/130552032545/important-info

From the official tumblr of the game, we get an interesting message from who we can presume is Sans. The first few paragraphs are a small rant from Sans' perspective, but the last two paragraphs is the interesting part.

Not only does he bring up the same line the Grey headed NPC says, but says that 'Not everyone is as tough as my brother.' Now, this sentence wouldn't be talking about Papyrus, as you and Sans early on in the game would talk about Papyrus' lifestyle and the 'cool' things he does in his life, like struggling to 'solve' the horoscope and him taking cooking lessons that aren't going so well. Sans doesn't seem to mind the gossip there, so could he potentially be talking about Gaster? Is Gaster actually his brother?

Shyren's body itself does seem very out of place, but when you think about it, during the credits only Shyren's face is there, no body to be seen. Shyren's head and body are specifically two different entities, This is most likely due to animation reasons, and the fact that Lemon Bread also uses this body type, but when you kill Shyren in a Genocide run, her head disappears and her body remains, which is a curious thing to note. This isn't really what you'd call anything to hint at, but perhaps looking at things related to Shyren could be a place to start.

Give it some time. This section will be updated when most of the rush to find new information has blown over.

All of the findings in this guide are not mine. This is merely my place of storing them, and perhaps giving people a central hub to share their findings.

All of my credits go to the anons in the fullchan and halfchan threads working hard each day to try and figure out the secrets that this game holds.

Another special thanks to the people that uphold the Timetraveller's guides, and Speedy for doing the cleanup on the logo's image.


I quite franky don't give a damn if it ain't halloween, this pumpkin's staying here forever.

https://www.dropbox.com/s/yyorjpkfkmak4ez/POSSIBLE%20GASTER%202.webm?dl=0

Located in room 272.

Checking this room without altering something else just gives you a dog. We're still working on this, and will update this when more info is available.

The wingdings in it read:
* [REDACTED]
I hope steam doesn't block these webms.

For your sake, please turn down your headphones / speakers. I won't take responsibility in those going bang.

This is an incredibly loud webm. You have been warned.

https://www.dropbox.com/s/4jecc2tcs95m86v/LOWER%20YOUR%20SOUND.webm?dl=0

An anon in a thread managed to find this peculiar room containing the bridge flowers. The path to the right leading to an INCREDIBLY LOUD rendition of Flowey's theme, leaving the player stuck in a text loop. There are also bizarre red pillars, which look very similar to streams of lava. Take note that right before the loud music blares, you can very briefly hear the Game Over song.

We have no idea how you get here yet, and we believe this room to be some kind of test room used by Toby at one point.