#cellytheory

Section II - The Deltarune Connection (The “Where”)

If you’ve read some Deltarune theory posts, you know that Gaster is prominently featured in Deltarune. He addresses us at the beginning of the game and there are blatant references to him (the phone call in the Dark World, the strange bunker, etc). I’m going to try to prove that Sans will also play a large role in its story. Let’s take a look at the lyrics of the end credits, Don’t Forget. 

When the light is running low And the shadows start to grow And the places that you know Seem like fantasy There's a light inside your soul That's still shining in the cold With the truth The promise in our hearts Don't forget I'm with you in the dark

The truth: Sans says this to us before giving us access to his room, the entrance to which is suspiciously identical to the fast-travel doors that Darkners use. We also get access to his basement.

Promise: Sans has a history of promises. He is regretful of a promise he made in the past.

Don’t forget: Appears on a poorly drawn picture of three smiling people, in Sans’s basement. This phrase is also used in a description for "Memory” in the sheet music booklet from the Collector’s Edition. What do you know, it’s written in Comic Sans too. Go figure.

Now, let me introduce a character that is featured prominently in Deltarune, someone that is somehow related to Sans, someone who isn’t Gaster.

Ice-E is everywhere in Deltarune’s Hometown, but the only inkling we get of his existence is from Sans. The Ice-E word search that Sans gives us is interesting because the title itself is written in comic sans. 

In one of the hospital rooms, there’s a “1-to-10 pain scale using Ice-E as a model”. It’s an uncanny description of Sans. 

Ice-E is also characterized for its missuses of apostrophes. One might call it an “apostrophe-dog”.

Moving on.

Section III - Gaster (The “Who”)

Oh boy, this section is going to be absolutely massive. I’ll try my best to make the logical flow easy to understand. So we know that Sans did (will do) some pretty shady things in the world of Deltarune. To understand why, we have to examine how exactly Sans and Gaster are related. Let’s start with Ice-E since we know that he’s somehow associated with Sans.

The “Nightmare” variant of the Ice-E word search appears in fun values between 56 and 57. There is only one other snowman that appears in Undertale.

We are asked to take “a piece” of it. Let’s investigate where else this specific phrase is used. Following this trail of breadcrumbs reveals other phrases that Sans and Gaster-related things share.

Exhibit A: Gaster follower #2, “time and space”

The prophecy has something to do with Sans and Gaster. I’ll let the evidence speak for itself.

Exhibit B: Memoryheads, “be seeing you”

Memoryheads are the first amalgamate we encounter in the True Lab. Before their spare conditions are met, they are known as "      " (six blank spaces). Gaster is frequently associated with the number six. 

If we attack the Memoryheads, these statements flash by quickly in red text:

FAILURE

But it didn't work.

nope

Absorbed

Don't worry about it.

I'm lovin' it.

Occurs when the player tries to name themselves Sans.

We see the phrase “be seeing you” in only these instances. Below is the Sound Test Room that has a chance to appear if the fun value is set to 65. This is the only place that “Gaster’s theme” can be accessed in-game.

Exhibit C: The dump

“The abyss” makes an appearance again. It’s something to pay close attention to--it’s always somehow related to Gaster. So what does a piece of trash falling into the abyss mean? Well, we know that Gaster “fell” into his creation...

We know that Flowey refers to Sans as “Smiley Trashbag”. Papyrus states that Sans frequents Grillby’s, a “purgatory” and “hamburger abyss”.

(note: Papyrus is referring to a literal trash can here, but the implication that Sans is “trash-like” is here)

If it’s not clear what I’m getting to, then let me spell it out: Sans is a piece of Gaster, they are one and the same. Sans/Gaster took his “experiment” with Deltarune too far, possibly destroying the world and displacing him in Undertale. 

I’ll continue this in another post because it seems that tumblr is breaking.

Mus_smile is the track that plays in room_gaster. This is my personal opinion, but the character that is the most strongly associated with smiles is Sans.

And Sans is certainly intelligent enough to be the prime suspect for being Gaster. The proper name for his namesake is Comic Sans Microsoft, or Comic Sans MS. MS can also be used as a suffix for the name of a person who has a degree in a Master of Science.

Sans also owns quantum physics books. The subject of Gaster’s scientific research is revealed in Entry #17: “photon readings negative”. Photons are described as a "quantum" of electromagnetic energy, and are of course within the realm of study under quantum physics.

Gaster, like Sans, is brilliant yet slow-working. Slower than Alphys, who is repeatedly noted to have nothing to show yet as the royal scientist in the eyes of the people and is shown to slack off constantly.

Gaster is implied to have perished, and I suppose he did, in a way, if these speculations do end up being correct. However, there’s something more to this statement. Ghosts are sort of in the realm of being not-alive, and Sans and Napstablook have a surprising level of comparability.

They both:

Get likened to “garbage”

Have connections to snails (Napstablook runs the snail farm)

Speak completely in lower case

Pretend to sleep and say “Z’s” out loud

Have black “sclera”

And the black sclera is also a topic of its own; it’s equated with the status of being brought back to life. Being “determined”. (See: Asriel and Undyne)

Undyne is especially suspect due to the strange right-eye-phenomenon she has in common with Sans, with spears shooting out of hers. Spears that are actually colored light blue, not unlike Sans’s eye. 

To recap: 

Sans and Gaster are heavily involved in Deltarune

They have been displaced from time and space

They have connections to snails

They are both doctors with knowledge in quantum physics

They both “fell” into the abyss

They both talk similarly

They are both slow

They are both characterized by their smile

They are both some degree of dead

Sans is Gaster or a significant piece of him. Sans has Gaster Blasters because they belong to him. If all prior conjecture proves true, he is and will be responsible for the destruction of a world or THE world within Deltarune. After all, the Latin definitions of “gaster” and “sans” are to destroy and to be without, respectively. 

That brings us to the next subject: why is Sans Sans? More specifically, why is that his name? Why even change his name?

Below is the Japanese version of the fun event with Sans’s phone call. It features completely different dialogue from its English counterpart. 

Am I Licca-chan? (Select No) Then from now on call me Sans. I need to check every once in a while. I won’t know when my name has changed. 

“Licca-chan” is a well-known Barbie-esque dress-up doll in Japan, so popular to the point where it is even used as a synonym for other dolls from different companies. Perhaps it implies that Sans is adaptable due to Licca-chan’s nature as a doll and how she is in a constant state of change to reflect the times. It also seems to be a pun on “liquor” because Sans was talking about beer in the English version. I tried to scour the Japanese fandom for clues, but they also seemed stumped. If anyone has any ideas on what this could mean, please let me know!

Regardless, “Sans” doesn’t seem to be his actual name. Perhaps his true name was Gaster...?

Additionally, If the player changes the name of the fallen child via going into the code, this message appears in the stats menu. The vernacular is very Sans-like, with his frequent use of question tags at the end of his sentences (I counted 14 huh’s from Sans).

Finally, let’s talk about the number six. We know that it’s Gaster’s number--All of the explicitly Gaster-related fun events trigger for fun values in the sixties, Gaster’s stats are all comprised of 6′s, Gaster’s “typer-value” is 666--you get the idea.

The concept art Toby drew for the Alarm Clock’s character screen features what is presumably Sans and the number six.

“The Choice”--the track that plays during Sans’s judgements--is “Undertale” slowed down by 666%.

Section IV - Angels and Demons (The “Why”)

In modern day culture, 666 is closely associated with the devil. The Book of Revelation (13:17-18) asserts that 666 is “the number of a man” (this is important, and we’ll come back to it later) and is “the number of the Beast”. The Beast is mentioned as “coming out of the abyss”. 

Sounds a lot like someone else we know, doesn’t it? And how fitting for Sans, the one who judges our sins and demands us “to burn in hell”.

But if we go further, the Beast of Revelation is described to have seven heads representing seven kings. The beast itself is an eighth king who is of the seven and "was and is not and shall ascend out of the bottomless pit, and go into perdition." 

Chara is an eighth of the seven fallen children. 

There’s something Chara, Sans, and Gaster all share, and it’s their association with demons.

Here is an excerpt from the Cutting Room Floor:

Among the four strings in version 1.0, the last one, designated by variable “demond”, stands out for two reasons. 

 The letter “d” is separate from the other letters denoting the demon variables--the rest, “x”, “y”, and “z” are in sequential alphabet order.

The speech pattern of the last string is different from the others. It has that signature question tag at the end of the sentence that a certain character is known for.

In version 1.001, the strings clearly reflect Chara’s speech pattern. This time, all the variables are in sequential order from “a” to “d”. 

Pieces of dialogue at the near-end of a genocide route from Chara and Sans. Recall that Chara is using the same “Now” from earlier with Gaster and Sans.

Chara makes a reference to Banana Yoshimoto's book “Kitchen”. Take note of the page number.

Chara is also linked to the number nine. It’s the highest achievable stat in-game. It’s the stat of the locket and real knife. It’s how much damage Chara deals. It’s also the number six flipped upside down. 

The connections are undeniable. 

And yet, it goes further. Let’s take a look at how Christmas comes in to play.

In Deltarune, there are a few references to it, the most foremost probably being the importance of Noelle Holiday as a character. We also get Lancer’s laugh and the joke with “Krismas”.

Back to Undertale, there is significant Christmas iconography represented by “Gyfmas” and Gyftrot (bearing a strong resemblance to Photoshop Flowey, the DT Extractor, and Gaster Blasters).

What I’d like to focus on is Santa.  Papyrus describes him as “a chubby, smiling man who loves to surprise people.” From the thank you note addressed to Santa we find in Sans’s room, we can assume that Sans is a Santa, at least to Papyrus. It’s pretty fitting, since Sans can be described as someone who “knows if [we’ve] been bad or good”. Maybe he can even tell if we’re sleeping or awake with how the Dark World appears to be linked with sleep and dreams (please read my theory on Sans being a Darkner for more on this).

So we can reasonably conclude that Sans presents himself as a friendly, child-oriented figure, in-line with the nature of Comic Sans, a font for children, and Ice-E, a mascot of a company marketed towards children.

…

Santa is an anagram of Satan. 

…

To recap: Gaster’s association with the number 666 marks him as a “demon”. Chara and Sans are also called demons and similarly have connections to the number 6. This is more evidence that Gaster and Sans is or used to be the same people, and Chara has some form of correspondence with them.

I failed to mention before that there is actually a second Beast of Revelation “from the Earth” with "two horns like a lamb”. From the “earth” like Flowey, with horns like Asriel. 

Asriel is most likely the “Angel” depicted in the prophecy within the scope of Undertale; he’s named similarly to Azrael, an angel of death, and one of his attacks is literally called “Angel of Death”. He also bears a striking resemblance to the Deltarune in his God of Hyperdeath form.

Surprise, surprise, he and Sans also share parallels. 

Let’s start with their introductions. “Flowey the flower”. “Sans the skeleton”. It’s a similarly alliterative greeting and they’re both using fake names.

Mirrored dialogue yet again...

…and similar meta-commentary.

These three characters--Sans/Gaster, Chara, and Flowey/Asriel--they have all fallen. Gaster fell into his creation. Chara fell into the Underground. Asriel had “fallen down”. (Sans and Papyrus are also the only sibling pair other than Chara and Asriel. I won’t talk about Papyrus in this part though because this thing is shaping up to be too long already.)

What does this mean for Sans? I have a personal theory.

Above the entryway of the Judgement Hall, there is a reversed Deltarune. The triangles are inverted and the wings are more bat-like. In the room where only Sans appears, the same room that plays a version of “Undertale” slowed down 666%.

I think Sans is a candidate for the Angel prophesized to destroy the world in Deltarune. I think he is Sans Serif, a seraph. He fell into his experiment and became a “fallen” angel, a demon. 

The Angel’s Heaven mentioned alongside, on the other hand...  Heaven can also be used to refer to God. Dog is an anagram of God. 

Sans has many, many connections with dogs, especially one Annoying Dog. More on this next time.

1. Sans has connections to the Deltarune universe

Let’s list off what we know for sure:

Sans instantly recognizes the Player as a human and has knowledge of the Surface.

In the conversation at MTT Restaurant, Sans confesses that he knows the feeling of wanting to go home.

According to the Snowdin Shopkeeper, Sans and Papyrus showed up one day and “asserted themselves”.

In his lost soul dialogue, Sans says that “you’ll never see ‘em again”.

During his battle, Sans reveals that he “gave up trying to go back a long time ago” and that “getting to the surface doesn't really appeal anymore, either.”

After being defeated, Sans says that he’s “going to grillbys”. In Deltarune, the first place we see Sans is at Grillby’s. Sans’s house and the restaurant in Deltarune are the same as in Undertale (except for slight alterations like the lack of snow and...’sans)

Undertale!Sans and Deltarune!Sans have identical sprites.

After talking with the Clam Girl and learning of Suzy, you can go to Sans’s workshop and find a card sticking out from the back flap of the binder, described as a poorly drawn picture of three smiling people with the words "don't forget" written in lowercase. Deltarune’s credits song is titled “Don’t Forget”.

We can safely assume that Sans came from another place that is not the underground nor the surface; Sans misses his home and his friends there (presumably the people in the picture); Susie and Suzy are related somehow. Additionally, we can speculate that Sans and Papyrus may have arrived from another dimension. It might very well be the case that Sans originated from the Deltarune universe: Sans is completely resigned to the fact that he can’t alter the past no matter how hard he tries. Deltarune’s prophecy is all about inevitability. Sans’s defeatist attitude might stem from this.

Here’s some evidence that is more debatable:

River Person warns the Player to “Beware of the man who came from the other world”. It’s possible that the man in question is Sans.

I’ve noticed this isn’t brought up as much, but Sans’s word search is from ICE-E’s, which is a brand we only see in Deltarune. As far as we know, there is no trace of this brand in the Undertale universe. It definitely doesn’t appear to be one from a newspaper—it’s a distraction given to kids at restaurants.

BONUS: There’s a wacky inflatable mascot that resembles the ICE-E’s mascot in the dog shrine found in the skelebros’ house (console version)

During Shyren’s encounter, if the Player hums twice, the flavor text describes Sans selling tickets made of toilet paper. Now, we know that all the food in the Underground is made out of magic. Magic nourishes monsters, but it doesn’t pass through their bodies as waste. Why does Sans have toilet paper? 

Alphys seems to be in-the-know about Sans’s time-space shenanigans. In the epilogue of the pacifist ending, there’s some dialogue that suggests Alphys and Sans are quite familiar with each other. Both of them want to keep this a secret for whatever reason. In a neutral ending in which Alphys becomes the ruler, she is mournful of the deaths of Undyne, Alphys, and Asgore, but is glad that “at least Sans is here”. In the MTT quiz, if you pick “Don’t Know” to the question about her crush, Alphys reveals that she has done research on alternate universes and knows they exist. Both Sans and Alphys have connections to Gaster, who is quite prevalent in Deltarune. She, along with Sans (and coincidentally, the ICE-E word-search) are affected by Fun values and have their own Fun events. It seems a little random, but what if all the Fun events are Gaster-related? Are Alphys and Sans the two people mentioned in Entry 17?

So I think all of these pieces are sufficient in establishing Sans’s connection to Deltarune, though it is still unclear whether Sans came from Deltarune into Undertale or vice versa, OR Sans showed up from yet ANOTHER universe. That’s a theory for another time, though. On to the next part!

2. Sans has abilities/properties exclusive to Darkners

Some of the basics:

Sans can teleport, that is, use “shortcuts”, as evidenced by appearing both in front and behind the character in Snowdin, going to Grillbys, chasing after Papyrus in the wrong direction during the Pacifist ending scene, etc. Though Rouxls Kaard is shown to teleport, Lancer’s style of teleporting most closely resembles Sans’s. There are multiple instances in which Lancer stays ahead despite the Player passing him (for example, Lancer sneaking a sign past the party despite there only being one way to the door).

The door to Sans’s room greatly resembles the fast-travel doors that only Darkners are able to create. If you get the key to his room, the pitch-black and seemingly-endless walkway is not dissimilar to that of the supply closet. Papyrus also happens to liken Sans’s room to “another world”. All of the weird junk could be representative of various landmarks in the dark world.

Sans can manipulate shadows as seen through his first appearance (I also like to think that this is the reason why his “eye-lights” can disappear). This is most prevalent with Ralsei, Lancer, and the King obscuring parts of their body with shadows.

Darkners have colored portraits. At first glance, you would assume Sans doesn’t have one, but his head is already—conveniently—black and white.

If that wasn’t enough, let’s take a look at Sans’s battle in the Genocide Route. The most distinguishing feature of this fight is Sans’s ability to dodge your attacks, an ability that was thought to be unique to him. As it turns out, Darkners are also able to dodge (provided that they are warned). In order to actually beat Sans, you need to tire him out, and once you have dealt the final blow, he runs away. Sounds familiar, doesn’t it?

I believe that Sans actually survives the encounter as well. I’ve seen people claim that when he goes off-screen, the “dusting” sound effect signifies that he dies. This is wrong. That sound effect plays at the end of every battle, regardless of whether you spared or killed an enemy. I’d like to point out that the EXP you gain from the battle does not confirm Sans’s death. If you pick on Loox, you can get 5 extra EXP stacking up to 3 times. This means that killing an enemy is not required for you to gain EXP. I’ll also include that the kill counter doesn’t go up once Sans’s battle is over. It’s believed that this is the case because of Chara’s interference, though I don’t personally agree.

Let me also present this tidbit that I see no one else talking about: unlike literally any monster in the underground (besides Flowey, but he doesn’t count), Sans HAS NO HP BAR. When he gets hit, the damage numbers are present, but the HP bar that should have appeared above him is absent. Darkners don’t have a visible HP bar when struck.

Here’s some stuff that’s a little bit more controversial/speculative:

Lancer more or less implies that Darkners bleed, though we haven’t seen any examples of this yet. Ralsei doesn’t correct him, however. We know that the monsters in the light world don’t bleed (“Does it hurt to be made out of blood?”), and Susie’s comment (“Everybody bleeds, right?”) could be read as her trying to look cool for Lancer. Then, does Sans bleed?

It has been confirmed by @nochocolate​ that the red coming out of Sans is the exact same red as his ketchup bottle. This is a deliberate choice, but it doesn’t completely deconfirm that it may be blood because we don’t have other instances of blood to compare it to. Additionally, there is a mention of both blood and ketchup from Noelle: "This isn't another trick, is it, Kris? Like when you put ketchup on your arms and told me it was blood?" This might just be Toby Fox poking fun at the fandom or intentionally misdirecting us—really, it could go either way.

Sans’s mouth doesn’t move at all while he talks. It turns out that there may be an explanation for this! In Undertale, you can see the mouths of face sprites move while words are being spoken.

However, in Deltarune, both Lightners and Darkners don’t feature moving mouths in their textboxes! In instances wherein the full-body sprites are shown (Papyrus date, Alphys date, literally all the battles), the mouths don’t move either. So while his expression rarely changes, it might turn out that Sans DOES actually move his mouth while speaking, we just can’t see it. I’m a bit iffy on this theory since it varies from monster to monster in the Light World. Moreover, in Undertale, while Mettaton’s mouth doesn’t move at all (I’m going to disregard this since he is a robot) it’s very peculiar that the same can be said for Alphys.

Seriously, why doesn’t Alphys’s mouth move at all?? This HAS to be intentional, all of the other characters with a face sprite have moving mouths. Deltarune!Alphys doesn’t have one either. This brings up more questions than answers: Are certain monsters Lightners and others not? Is Alphys a Lightner? Did her “research” on alternate universes involve her actually traversing the multiverse? Am I overthinking this? In any case, it’s more stuff linking her to Sans...

If it turns out that not all monsters are Lightners, then it makes sense that Sans is so devoted to Papyrus, assuming that Papyrus is, in fact, a Lightner. No other person’s death makes as much of a difference as Papyrus’s concerning Sans’s behavior towards you. Alternatively, if Papyrus is not a Lightner, then it stands to reason why Sans is so depressed—he has no way of fulfilling his purpose. “Sans”, after all, means “without”.

The Light World has virtually no indications of monsters being able to use magic. In Undertale, it’s stated that magic is a method of self-expression for monsters, yet the only magic we see in Deltarune is from within the Dark World. If we compare Deltarune!Toriel’s stovetop to Undertale!Toriel’s, we see that the flavor text has omitted her use of fire magic. Susie is able to send out magic ax attacks, but this is likely due to the nature of the Dark World. I need to clarify that she is not the one that casts the Pacify spell at the end of a “neutral” run; she realizes that the King is tired, and waits for Ralsei to finish the job. Her remembering Pacify is exactly what it means, and Ralsei comments on it because he is expressing surprise that she cared to remember the spell she made fun of him for. I’ll also point out that the lack of magic would be the reason why the monster-human war ended differently/didn’t even happen, therefore allowing monsters to reside on the surface. If Sans did hail from this world, he wouldn’t have magic or would have very limited magical capabilities if he isn’t a Darkner.

Here is a piece of dialogue from Sans about the Underground. Interestingly, he differentiates himself from monsters, though this could just be because he doesn’t want to lump in Papyrus with them. The King has a similar line (“Show my son the monster you REALLY are!”). Monsters are possibly complicit in Darkners’ imprisonment. Is it possible that Sans is also resentful? Do Darkners exist in Undertale?

I feel like this interaction is worth mentioning. It’s entirely possible that Darkners were sealed so long ago in the Undertale universe that nobody even remembers their existence. 

Going back to Papyrus, if Sans is a Darkner, then it’s important to mention that Papyrus is not. We see Papyrus turn to dust when he is killed. For that reason, it seems that Sans and Papyrus are not biological brothers. I think this actually makes a lot of sense given how different they look. Yes, it’s true that Sans and Papyrus both have a skeleton motif, but they don’t look remotely similar. The face shape, the jaw, the build, the height, the eyes, the nasal cavity—nothing matches! Each monster species look the same, hell, even boss monsters like Toriel and Asgore resemble each other. Compared to Papyrus, Sans seems a lot more solid (his gut) AND he’s almost completely covered up save for his face (what are you hiding under there?).

Their bone attacks are distinct as well: Papyrus’s have a more angular aesthetic compared to Sans’s rounded edges.

In comparison, Toriel, Asgore, and Asriel have the same exact fire attack.

So, if Sans is a skeleton-themed Darkner, what type would he be?

3. Sans is the Ace of Spades

This part of the theory is a bit more conjectural, but I think there is enough evidence to put this in here.

Let’s start with how Sans, Lancer, and the King are similar:

Their sprites have the same color scheme: black, blue, white, and grey.

They sport uneven and toothy grins, are round and chubby (“if you eat too many hot dogs…you’ll probably get huge like me”), and have a hood.

The spades seem to have a smile motif. The grinning “mouth” of the Card Castle has the same number of “teeth” as Sans. Additionally, you can see portraits of spade people inside the castle. They’re all smiling.

These three are the only characters that can freely shift between being completely submerged in the shadows and becoming visible. The ability to cloak their body with shadows is a trait thought to be shared by all Darkners; Ralsei, after all, exhibits this all throughout our journey. What’s interesting is that there are clear parallels to Sans, Lancer, and the Kings’ shadows: they conceal their entire form and reveal it during their first appearances.

Sans and Lancer are shown to be able to teleport. I’m bringing this up again because it seems that not all Darkners can teleport without the use of a door as indicated by Ralsei’s confusion. If Ralsei has extensive knowledge of Darkner powers, and he is unaware that Lancer can teleport, then teleportation must be an ability unique to the spades, or, at the very least, card-themed Darkners.

Sans and the King’s fights are eerily similar. You need to fight/tire them out and listen to them monologue in order to progress. A major theme of both fights is how you can’t truly spare them. Appearing worn out from the battle, they appeal for mercy. Should the Player fall for it, they launch an unavoidable attack that deals catastrophic damage. Additionally, before his fight, the King employs the use of silent text, just like Sans during his judgments and his intimidating moments. Also worth noting: in both fights, the battle box is manipulated deliberately to suit the needs of the Player (for our last attack against Sans) and the King (his weird stomach tongue latching onto the box). Sans is also capable of stretching the box as seen with the attack before his special attack.

Lancer and Sans, in particular, parallel each other quite nicely. They are both playful jokers, they both own bikes, and both of these characters have a strange relationship with food (particularly with red condiments).

The two just so happen to have stands to sell questionable foodstuffs.

Sans is evidently constantly eating:

Undyne: “And his brother kept making 100’s of midnight snacks.”

Papyrus: “GRILLBY’S… IT’S DARK AND FULL OF GREASE. PURGATORY OF FRIES… HAMBURGER ABYSS… ANYWAY, MY BROTHER PRACTICALLY LIVES HERE.”

Big-Mouth: “Sans is interesting. He has told me about all kinds of incredible foods. But, despite his knowledge, he always orders the worst burger off the menu.”

And we know that Lancer barely eats at all. He doesn’t think that having three glasses of milk as his dinner is unusual, he’s not allowed to eat the Dark Candy, he pretends to eat the salsa in the stump, and he has to get fed worms by Rouxls because his father forgot to feed him. Sans and Lancer both have terrible eating habits. I’m not sure what this is supposed to mean, but you know, food for thought.

Why the Ace of Spades:

The designs of both Lancer and the King originated from @kanotynes​ who created an entire deck of cards. The Ace of Spades does not have a distinct design.

French manufacturers standardized the four playing card suits. “Sans” and “Lancer” are both French words.

It symbolizes uncleanliness and depression (Sans’s socks and his room, the latter is pretty self-explanatory), omens (River Person’s warning, Flowey alerting us to not reveal our abilities to him, “you’re going to have a bad time”), and death (the reason for his skeletal nature).

In Blackjack, Aces have a numeric value of 1 (matching his stats) or 11 (the same number of unique pre-battle dialogue from Sans, though this may just be a lucky coincidence). The Eleventh Hour is an idiom meaning nearly too late. Sans’s fight is your last possible chance at quitting before the world ends and your game gets corrupted.

Remember that bit where Sans has toilet paper? In the Card Castle, you can see that a bathroom, the Royal Flush, is occupied. Darkners have to digest their food. On a related note, the royal flush is a poker term for an A(14), K(13), Q(12), J(11), and 10 hand. Interestingly, in the sequence before his “special attack”, we see Sans disappear and reappear at the edges of the screen 14 times (again, probably just a neat coincidence).

The ace is paradoxically the least and most valuable card (in Blackjack, Poker, etc.), paralleling Sans being the weakest and strongest enemy.

Ace of Spades also represents “an end”, and Sans is there at the end of our journey, judging us before Asgore’s fight. He is also responsible for initiating the phone calls at the end of every neutral route.

Okay, this one is a little bit of a joke. In this deleted tweet, Toby said that Sans would be too lazy for sex, causing fans to speculate that he is “ace” lol.

BONUS: Sans was originally intended to run a casino. This one’s a bit self-explanatory. Also explains his poker face.

The most important piece of evidence, however, is this: the French expression fagoté comme l'as de pique means "(badly) dressed like the ace of spades." Checks out.

On Gaster Blasters:

Gaster Blasters might have a spade motif. If you connect the natural curves of the eyes and the top of the nose ridge, you get a spade shape. The GB's crests resemble King Spade's crown and possibly the neck/shoulder part of his cape.

A GB's nose resembles King Spade's when he isn't snarling at you; this might also apply to Sans if he stopped smiling (mouth shape affects the shape of their noses). 

Also on the topic of noses, Sans, Lancer, and King Spade's noses translate to the same shape in their overworld sprites.

The fog from Snowdin, which has been theorized to be either a front-facing GB or Sans' face (and honestly I lean more towards it being Sans's face because of the eye shape) has a hidden line underneath and above the nose. Perhaps Sans resembles the Gaster Blasters and the Spades more than we anticipated?