Sans

Sans (/sænz/, SANZ) is the older brother of Papyrus and a major character in Undertale. He first appears in the forest after exiting the Ruins. He serves as a supporting character in the Neutral and True Pacifist Route and as the final boss and heroic antagonist in the Genocide Route.

Appearance
Sans is a short skeleton with a dimpled smile on his face. He wears an unzipped blue hoodie, a white t-shirt or sweater (or not; debated), black shorts with white stripes, and a pair of sneakers (see overworld sprite) or slippers (see battle sprite).

He has white pupils, which tend to disappear when he is serious. When using magic, (specifically psychokinesis) his left eye flashes light blue and yellow, and his right pupil disappears.

Personality
Sans is shown to be lazy and laid back, sleeping on the job and taking breaks often. He enjoys making bad, skeleton-related puns; although the fact that he performs at MTT Resort hints that he may, in fact, be a talented comedian. He enjoys science fiction and loves to drink ketchup. In addition, he hates making promises.

He is kind and reassuring but becomes eerily serious at particular moments, sometimes causing his pupils to disappear leaving empty black sockets. He is also very observant; his lines and actions change from the protagonist's choices more than any other character's.

Sans's laziness is shown to be in fact a combination of fatalism and apathy. He wonders if his indolence stems from his knowledge of the fact that any progress he makes will be erased abruptly as soon as the timeline resets. Although he suggests it could be a poor excuse for being lazy, it is unlikely.

Judging by the quantum physics book, workshop, and broken machine found in his house, along with other evidence, Sans is heavily implied to come from a scientific background.

Abilities
Sans is shown to be able to move exceedingly quickly and/or teleport through his frequent use of "shortcuts," as he calls them.

In battle, he shoots what appear to be a kind of laser or beam using "Gaster Blasters," a device resembling a goat or dragon skull. These also bear similarities to the DT Extraction Machine found in the True Lab, Gyftrot's head, and Asriel's first form's head. During battle, he is shown to exceed in fighting skills compared to all other characters in the game (even Asgore and Undyne) with his tricks in attack layout, use of Karmic Retribution, and ability to change the effect of gravity on the SOUL.

He has obtained the knowledge of multiple timelines and the SAVE function, presumably through his scientific research. However, it appears he does not actually retain knowledge when the protagonist loads a SAVE, and cannot use the SAVE function himself. It may be that his awareness of the situation and his innate perception allows him to recognize when the protagonist is behaving unusually. He can tell when they have reset the timeline and can tell they have experienced events occurring in other timelines (such as the protagonist losing to Sans, then reloading their SAVE to where they had never fought him before).

Sans seems to know if the protagonist has achieved an impossible ending in the Neutral Route's phone call and will call them a "dirty hacker." Given that he dubs this as an "error handling message," he is aware of when the game's code suffers bugs as well.

Sans is also shown to have some skill in playing the trombone, though he is only seen playing it once. Papyrus finds his "incidental music" annoying, so he must play it on other occasions.

He can also recognize how much EXP the protagonist has, as he comments on it when he judges them. His magic also seems to react to EXP, given that his attack has a special ability referred to as Karmic Retribution that presumably would not be harmful if the player had little EXP.

Neutral Route
Sans first meets the protagonist after they walk out of the Ruins into Snowdin Forest. They are pursued by Sans, who first appears as a silhouette. After introducing himself, he explains that despite being a sentry, he has no interest in capturing humans, although his brother, Papyrus, does. He then hides the protagonist from his brother behind a conveniently shaped lamp, that just so happens to be shaped exactly like the protagonist, while he and Papyrus have a heated discussion of Sans's laziness and the importance of puzzles. Sans appears multiple times throughout Snowdin Forest, usually alongside Papyrus, observing and commentating on the puzzles but not actively engaging in any japery, except for the word search.

Sans is absent in Snowdin, although he appears abruptly during the protagonist's date/hangout with Papyrus, sticking out of his room with a trombone. If the protagonist kills Papyrus, Sans is absent throughout the rest of the game, until he resurfaces to give his judgment.

After entering Waterfall, Sans is found manning another sentry post and asks if the protagonist wants to hang out with them. If the protagonist agrees, he takes them to Grillby's via a "shortcut." Sans is greeted warmly by the patrons of the diner and proceeds to treat the protagonist to a burger or some fries. After some ketchup nonsense, a spotlight falls on him and the protagonist, causing a sudden, darkened mood. Sans then tells the protagonist that Papyrus has mentioned a flower has been talking to him and mistakenly believes that someone is tricking him with an Echo Flower when in reality the flower in question is Flowey.

Sans is met again in Waterfall and pranks the protagonist with a red-eye telescope.

The protagonist passes him sleeping at one of the sentry posts in Hotland when fleeing from Undyne. Once Undyne notices him sleeping, she becomes quite angry, causing her to stop to berate him.

Sans is also encountered later on in Hotland selling Hot Dogs for 30G. If the protagonist attempts to buy a hot dog with no room in their inventory, he will begin to place the hot dogs on their head for free. He will stack up to 30 total hot dogs, after which he will stop, stating that 30 is an excessive number and that he cannot reach high enough to place anymore. If the protagonist moves left or right with a stack of hot dogs on their head, the hot dogs will fall off, obeying gravity. It is possible to leave the room with Hot Dogs on the protagonist's head, but they will vanish when the next room is entered.

Sans is later found outside of MTT Resort, where he offers the protagonist to grab a bite at its restaurant. If they agree, he will escort them through one of his 'shortcuts' (if you go back and check the shortcut later, it will just be a brick wall). At the restaurant, Sans reveals he had befriended a woman (Toriel) with a similar affinity for puns that resided on the other side of the entrance to the Ruins. He tells the protagonist that the woman made a request to which he promised to comply: to watch over and protect any human who came through the door. He states that if not for his promise, the protagonist would be "dead where [they] stand," which he dismisses as a joke shortly afterward. He mentions how he is doing a good job at protecting the protagonist, though he will question it if they have died before. Before leaving, he tells the protagonist to take care of themselves, because there's someone who really cares about them.
 * If the protagonist has not died at this point of meeting up with Sans, he will mention that you have not died once the whole time rather than questioning if the protagonist has died before.

Judgement
While passing through the final corridor, Sans encounters the protagonist one last time. He proceeds to judge them for the EXP earned throughout the game, revealing that EXP stands for "EXecution Points", and that LOVE stands for "Level Of ViolencE." His judgment is determined by the protagonist's actions throughout the game.
 * If the protagonist gained no EXP, Sans will begin to talk normally and will skip his judgment, telling the protagonist that they never gained any LOVE, but that they gained love, and that they have always striven to do the right thing. He goes on to say how he appreciates the protagonist for having kindness in their heart, telling them that the monsters' fate is in their hands; they can either let Asgore take the protagonist's SOUL for their freedom, or take Asgore's SOUL for the protagonist's escape. He tells the protagonist that he believes their determination will help them do the right thing. He then leaves.
 * If the protagonist restarts from a SAVE Point after hearing his speech or has completed the Neutral Route before, Sans will take note that the protagonist has already heard this speech before and will give them a secret codeword. The protagonist can repeat this about two more times until Sans gives them the key to his room.
 * If the protagonist gains some EXP, Sans will allow them a moment to think of their actions. After a moment, he will begin to talk normally, and will tell the protagonist that all that matters is that they were honest with themself.
 * If the protagonist spared Papyrus but killed other monsters, Sans tells the protagonist that it will be left up to them to decide what will happen. He then leaves.
 * If the protagonist resets after hearing his speech, then returns to the Last Corridor, Sans judges the protagonist based on how high their LV is:
 * If the protagonist is at LV 1 but has more than 0 EXP, Sans presumes that they killed someone just to see what he'd say about it. He says " wow. you're a pretty gross person, huh? "
 * If the protagonist is at LV 2, Sans says that it is pretty sad that the protagonist messed up the slightest amount, and that they probably didn't know what they were doing, but then says that he is kidding, stating: " who gets to LV 2 on accident? get outta here. "
 * If the protagonist is at LV 3, Sans gives the protagonist a C+ and tells them that they can do better.
 * If the protagonist is above LV 3, Sans says that they probably killed some people on purpose, though maybe some of it were in self-defense, and that he is not sure, as he was not watching.
 * If the protagonist is above LV 9, Sans says that does not mean that the protagonist is 50% good, and questions " what can I say that will change the mind of a being like you...? "
 * If the protagonist is above LV 14, Sans will say that the protagonist is a " pretty bad person, " but that they could be worse, and that they " pretty much suck at being evil. "
 * If the protagonist resets again after hearing his judgment, Sans will comment that the protagonist still looks bored and that they should " consider our session over. "
 * If the protagonist killed Papyrus, Sans goes on to tell the protagonist that he suspects they have some special power, and asks if they think it should be their responsibility to do the right thing.
 * If the protagonist says "Yes," he then asks why they killed his brother.
 * If the protagonist says "No," he says that he will not judge the protagonist for their viewpoint, but calls them a "dirty brother killer."
 * Either way, he will leave after reminding the protagonist of Papyrus's death at their hands.

Endings
After the fight with Photoshop Flowey, Sans will call the protagonist, and inform them of the events that transpired after their departure. The content of this phone call varies depending on the protagonist's actions, and a list of the different endings which Sans can describe is found on the Neutral Route page.

True Pacifist Route
Sans will be absent from the final corridor in the true pacifist route. There is also no SAVE point or box upon entering the hall.

Sans appears during the cutscene that occurs after the protagonist initiates the battle with Asgore. Toriel recognizes his voice, and they meet face-to-face for the first time. Toriel recognizes Papyrus as his brother, saying that Sans has told her a lot about him. Sans, along with the protagonist's other friends, are bound by Flowey, yet still protect the protagonist against Flowey's attacks. However, Sans is absorbed by Flowey, along with all the other monsters and their souls.

During the battle against Asriel, Sans appears as one of the Lost Souls.

After defeating Asriel, Sans stands alongside the other main characters. If the protagonist talks to him, he says a certain remark depending on what, if anything, the protagonist said to Toriel in calls at the beginning of the game. Sans also uses Toriel's phone to text for her a few times, as Toriel's thumbs are too big for the phone buttons. After the protagonist is ready to leave, Sans exits the Underground and heads to the Surface along with the other monsters.

Papyrus runs off to introduce himself to the humans and Sans says someone has got to keep him away from trouble and runs off in the opposite direction presumably to use a 'shortcut.'

In the credits, Sans is seen riding a tricycle on a highway, while his brother races alongside him in a car. Papyrus seems irritated when his brother overtakes him.

Genocide Route
Sans stalks and introduces himself to the protagonist as usual, and although he recognizes the protagonist as not being human, he asks them to keep pretending to be human, as Papyrus has always wanted to see one. He goes along with Papyrus's japery, although he does not appear as an NPC as he does on regular routes. After the protagonist crosses the bridge, Sans warns them not to fight his brother, or else they'll "have a bad time." He then suddenly disappears and is absent until the final corridor.

If the protagonist aborts the Genocide Route by sparing Papyrus, Sans will reappear at the Waterfall sentry station, and tell the protagonist he respects them for doing that. He will continue to appear as if on the Neutral Route, but will not take the protagonist to Grillby's since there's no one left in Snowdin.

In the final corridor, Sans asks the protagonist whether or not a person can change. Not expecting an answer, he continues and asks if they " wanna have a bad time? ", warning them not to take another step forward. After the protagonist continues forward, Sans then engages a fight against the protagonist and apologizes to Toriel (who is dead) for breaking his promise ("If any human comes through, watch over them, and protect them.")

After a short monolog, Sans begins a furious onslaught of attacks against the protagonist, while contemplating why he has not done much to prevent the protagonist's actions. After he finishes his speech, Sans offers to spare the protagonist, telling them that accepting will make his job a lot easier.

If the protagonist spares him, he tells them that he will not let the protagonist's work go to waste. He then kills them, or "dunks them" as he puts it, with an unavoidable attack and asks them in the game over screen not to return if they really are a friend. If the protagonist does come back, Sans's second attempt to convince the protagonist to spare him is a little half-hearted, suggesting that he knows the protagonist has already fallen for it and is unlikely to do so a second time. When the protagonist attacks him, he says that means they never really were friends and asks the protagonist not to tell other instances of Sans in other timelines.

If the protagonist does not spare Sans, then the fight continues, Sans saying that it was "worth a try." Sans continues to assault the protagonist with further attacks, and the Flavor Text proclaims that "The REAL battle begins." After the protagonist dodges all of his attacks, Sans, in a desperate attempt to kill the protagonist, repetitively slams the protagonist's SOUL against the walls of the battle box 36 times. Though the protagonist loses 1 HP each slam, it will not decrement after reaching 1. Sans then uses his "special attack," which ends up being nothing (thus never ending Sans's turn), as Sans hopes that if nothing happens, the protagonist will quit out of boredom or simply remain trapped forever.

However, Sans eventually falls asleep, allowing the protagonist to push the bullet box so that they can select the FIGHT option. Other options are unavailable, and the box can only be pushed towards the fight button. Sans then dodges the first attack, thus using up his turn, and stood still long enough for the protagonist to deal the second attack (unprovoked by the player) which successfully hits him while in mid-sentence for 9,999,999 damage. He appears to bleed from his wound though it is speculated by some to be either ketchup or an injection of liquid determination. Sans reminds the protagonist that he warned them before getting up and slowly walking off-screen. Presumably hallucinating, he asks Papyrus (who is dead) if he would like anything from Grillby's. The death sound is heard from off screen, and the protagonist's EXP is set to 99999, granting them LV 20 (regardless of their EXP before the encounter – in normal playthroughs, it will always be 50000). If the Player resets after killing Sans and challenges him again, Sans notices a disturbing look on the protagonist's face and states that he " won't grace it with a description. " He becomes more disturbed by the protagonist's expression and says that they are " some kind of a freak " if they kill him and reset to challenge him again repeatedly.

Sans does not count as a kill in the Stats menu, and the game does not seem to record whether or not he is killed. In this way, the entire Sans fight can be skipped by changing the protagonist's room from 231 (room_sanscorridor) to 232 (room_castle_finalshoehorn) in their save file.

In Battle
See Sans/In Battle.

Protagonist
Sans is the first monster the protagonist meets outside the Ruins. His attitude towards the protagonist is mostly dependent on their actions, though he usually enjoys pranking the protagonist and occasionally hanging out with them unless they kill Papyrus. Near the end of the Neutral Route, he judges them depending on their actions. At the end of the True Pacifist Route, Sans considers them a good friend.

Sans initially considers the protagonist to be an "anomaly"; his intentions of befriending them were in hopes that they'd stop resetting the timeline. The only reason he does not kill the protagonist in Snowdin is because of a promise he made to Toriel.

Papyrus
Sans cares a lot for and admires his brother. He reads him bedtime stories and gives him presents under the identity of Santa. Nonetheless, he likes to mess with him as he would with anyone else. (example from Papyrus date, when Papyrus says " A JEALOUS TROLL HAS BESIEGED MY ONLINE PERSONA, ALWAYS SENDING ME BAD PUNS IN A GOOFY FONT. ")

Sans is worried about others hurting Papyrus or taking advantage of him. If the protagonist kills Papyrus, Sans will resent them greatly and disappear for most of the game. On various endings, Sans is afraid to tell Papyrus about other characters' deaths, so he lies about them going on a vacation.

In the Genocide Route, Sans will also warn you not to kill Papyrus. His eyes disappear showing that he is dead serious and afterward disappears entirely, expecting the protagonist to comply.

Toriel
Toriel and Sans are close friends, sharing a love of bad jokes; though they never see each other in person until the end of the True Pacifist Route, the Family Ending, or the Exiled Queen Ending.

In the Exiled Queen Ending, Sans becomes Toriel's roommate if Papyrus has been killed. In this route, Sans also states that he "can't bear to tell her what (the protagonist) did."

If Papyrus was not killed, Sans and Papyrus visit Toriel often, play board games together, and sometimes convince Toriel to leave the Ruins.

While not being one to keep promises, Sans complies with her request to watch over and protect any human that passes through the door exiting the Ruins. At the end of the Genocide Route, he indirectly apologizes to her, as he is forced to break his promise to stop the protagonist.

Flowey
In one of the Neutral Endings, Flowey calls Sans "Papyrus's garbage brother" and "smiley trashbag." He says he tried to experiment with Sans using his SAVE ability. However, Sans "caused more than [his] fair share of resets," as if Sans was just about the only thing capable of stopping him, much like it is for the protagonist on the Genocide Route.

Alphys
It is hinted that Sans and Alphys have a history, possibly working under W. D. Gaster. Just before heading to the surface in the Pacifist Route, Alphys jokes that everyone has been fighting for the ability to watch anime on the Internet, as does Sans. She jinxes him and says she knew he would make the joke. Papyrus inquires as to how they know each other. Alphys stutters ineffectually before Sans covers for her.

W. D. Gaster
There are a few things that hint a connection between Sans and W. D. Gaster. These include the blueprints found in his workshop and the veiled machine, the sprites used for his skull-like laser gun attacks are labeled gasterblaster, and his knowledge of the "anomaly" eventually causing the destruction of the world in a Genocide Route.

Trivia

 * Sans's name alludes to the typefaces in which he speaks in, Comic Sans and Sans Serif (when he projects hostility). This is a reference to Helvetica, a webcomic about a skeleton named after a font. His name is also a pun due to his comical personality. The word "sans" means without.
 * Papyrus also has this allusion, considering he always speaks in Papyrus's typeface.
 * If the player attempts to name the Fallen Child "Sans", the game responds "nope." and prevents the name from being used.
 * He makes a brief appearance alongside Papyrus at the end of the Undertale Demo if the protagonist does a pacifist playthrough.
 * In the Genocide Route, Sans will not acknowledge the fact that the player had turned around to shake his hand before he told them to if the player has reset or reloaded their save file.
 * Sans does not make any puns in the Genocide Route - this is unusual for his character.
 * Sans, along with Undyne, are the only characters in the game witnessed playing an instrument, with Sans playing the trombone, and Undyne playing the piano.
 * Sans appears to be left-handed. Evidence includes:
 * Greeting the protagonist with a handshake using his left hand.
 * Holding and drinking a ketchup bottle with his left hand while dining at Grillby's.
 * Steering a tricycle using his left hand, while keeping his right hand in his jacket, in the True Pacifist Credits.
 * Manipulating gravity with his left hand in his boss fight.
 * Sans may call the protagonist to ask if their fridge is running in Snowdin Forest.
 * Despite being a skeleton, Sans's hand does not resemble a skeleton's. This abnormality can be explained with him wearing gloves, as his hometown's climate is cold.
 * This statement can be countered by the fact that Papyrus says he does not get cold, as he is a skeleton with no nerve cells. Moreover, he also has standards.
 * This statement can be countered as well because Sans might just like the look of them.
 * Killing Sans does not increase the protagonist's kill count.
 * During the fight with Sans, his eye flashes Yellow and Light Blue, the SOUL colors for Justice and Patience. These colors make sense as he delivers justice to the protagonist in a Genocide Route (being just about the only thing that can stop them) and is patient, not interrogating the protagonist until the very end of their journey through the Underground, as well as his 'Final Attack'.
 * During the Sans fight, he says, " ... you'll just keep going. not out of any desire for good or evil... but just because you think you ' can ' ... ... ' you have to. '  " This quote could be referring to the "completionist" type of gamers, who do everything they possibly can in a game because they felt they must.
 * It is implied that Sans will follow the Protagonist if they have killed Papyrus.
 * There is a glitch in which Sans will walk up off the screen at Grillby's when he takes the player there. His dialogue will still appear normally nevertheless.
 * Sans is the only character in the game that dies off-screen. This leaves the Schrodinger's cat effect for players.
 * Sans's first dialogue in his fight is a reference to Asgore's dialogue in the Neutral route. They both say "Birds are singing, flowers are blooming..." but the following dialogue is different. This projects the feelings to the protagonist depending on what they have done: Asgore is more calm and collected, and Sans is cursing the protagonist for Genocide.
 * Sans's Lost Soul's dialogue is displayed in the usual font (instead of Comic Sans) and sways back and forth. The only other instance of dialogue swaying is Woshua's dialogue.