Sans

Sans ( [sænz ], SANZ) is the older brother of Papyrus, and first appears in the forest outside Snowdin Town. Sans is a major character in Undertale, and depending on the protagonist's actions, is either a supporting character or a heroic antagonist.

Appearance
Sans is a short and big-boned skeleton, wearing a hoodie or simple jacket, unzipped at all times, with a white shirt, black shorts and sneakers according to his Steam trading card (can be also interpreted as slippers as seen in the official merchandise).

He is seen with a grin at all times, and only moves the corners of his mouth at certain scenes. He has white pupils, which tend to disappear when he is serious. A bright, flashing iris appears in his left eye during the battle against him, as well. This eye starts off merely glowing, but as he utilizes his time warping powers, it starts to flash vividly.

Abilities
He has obtained the knowledge of multiple timelines and the SAVE function, presumably through his scientific research, as can be found in Sans's room (possibly with the aid of W. D. Gaster). However, it appears he does not actually retain knowledge when the player loads a SAVE (although he cannot remember when the protagonist has performed a reset), 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 player is behaving unusually.

He likewise is shown to be able to move exceedingly quickly and/or seemingly teleport with his frequent use of "shortcuts" to get places. During battle, he can shoot what appears to be a kind of beam using multiple "Gaster blasters" (the name of his weapon's sprite in the files), a device which resembles a goat or dragon skull. The gasterblasters also bear similarities to the DT Extraction Machine found in Alphys's True Lab, Gyftrot's head, and Asriel's first form's head.

Personality
Sans is shown to be very laid-back, sleeping on the job as often as he takes breaks. He enjoys making bad puns relating to skeletons, to the annoyance of his brother. He is kind and reassuring, but becomes eerily serious at abrupt moments (particularly when angry).

He is also very observant, and his lines and actions change more in relation to the player's choices than any other character. He knows the number of times he had defeated the player (in Genocide Route). He hates to make promises, although he promised Toriel he would protect the player.

His laziness is noted during the final fight in the genocide route - he is unsure if being somewhat aware of the timeline resetting has broken his spirit, knowing that everything he does will mean nothing... or if he's just using it as an excuse to slack off.

Although he does not outwardly show it, Sans exhibits depression, evidenced by his lack of motivation and feelings of hopelessness to the point where he is willing to give up. His depression stems from his knowledge of multiple timelines and the SAVE ability, knowing that even if monsters escape the Underground, the timeline will be reset and the monsters will just end up back in the Underground without retaining their memories. Sans is also fully aware that his own life is already forfeit.

Neutral Route
The protagonist first meets Sans after exiting the Ruins into Snowdin Forest, where the protagonist is pursued by Sans, who at 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, 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 Town, although he appears abruptly during the protagonist's date with Papyrus, sticking out of his room with a trombone. If the player kills Papyrus, Sans is absent throughout the rest of the game, until he resurfaces to give his judgement.

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, Sans takes them to Grillby's by using 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 Sans, and Sans reveals to the protagonist that Papyrus has mentioned a flower that has been talking to him, and mistakenly believes that someone is pranking him with an Echo Flower, when Papyrus is actually talking with Flowey.

Sans is later encountered again in the 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 Sans. Sans is also encountered later on in Hotland selling hot dogs.

The protagonist later encounters Sans outside MTT Resort, where he offers to grab a bite at the MTT Restaurant. If the protagonist agrees, Sans will escort them there via one of his shortcuts. While in the restaurant, Sans reveals that he had befriended a woman that had a similar affinity for puns and resided on the other side of the entrance to the Ruins. Sans then told the protagonist that the woman made a request: to watch over and protect any human who came through the door, which Sans promised to obey. Sans states that if the promise had not been kept, the protagonist would be "dead where they stand." Sans then says that he's joking, and changes the subject to how he's doing a good job at protecting the protagonist, though if the protagonist has gotten a game over, he questions whether or not he's wrong. He then tells the protagonist to take care of themselves, because there's someone who really cares about them, before exiting the room.

Judgement
While passing through the final corridor, the protagonist encounters Sans, who then proceeds to judge the player for every point of EXP earned throughout the game. Sans reveals that EXP is an acronym meaning "execution points" and that LOVE stands for "level of violence". His judgement is determined by the protagonist's actions throughout the game.
 * If the protagonist gained no EXP, Sans will begin to talk normally, telling the protagonist that they never gained any 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 resets from a save point after hearing his speech, Sans will take note that you've already heard this speech before and will give you a secret codeword. The protagonist must repeat this about two more times until Sans gives you the key to his room.
 * If the protagonist gained some EXP, Sans has a few different things he may say.
 * If the protagonist spared Papyrus but killed other monsters, Sans tells the protagonist that it will be left up to the protagonist to decide what will happen. In certain conditions, Sans judges the protagonist based on how high their LV is.
 * If the protagonist is at LV 2, Sans says that it's 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's kidding, stating: "who gets to LV 2 on accident? get outta here."
 * If the protagonist is at LV 3, Sans gives you a C+, and tells you that you 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 was in self defense, and that he's not sure, as he wasn't watching.
 * If the protagonist is above LV 9, Sans says that that doesn't mean that the player 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 killed Papyrus, Sans goes on to tell the player that he suspects they have some sort of 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 won't 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 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 the souls of all the other monsters.

During the battle against Asriel, Sans appears as one of the lost souls.

After defeating Asriel, Sans stands alongside the other main characters. If you talk to him, he says a certain remark depending on what, if anything, the protagonist said to Toriel at the beginning of the game. Sans also uses Toriel's phone to text for her a few times. 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's got to keep him away from trouble, and runs off in the opposite direction presumably to use a "shortcut". In the credits, Sans is seeing riding a tricycle on a highway, while his brother races along in a car.

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

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 to not take another step forward. After the protagonist continues forward, Sans then engages a fight against the protagonist, and apologizes to Toriel (who is absent) for breaking his promise to protect the protagonist.

After some short monologue, 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 won't let the protagonist's work go to waste. He then kills them 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, with Sans saying that it was "worth a try". Sans continues to assault the protagonist with further attacks, and the textbox 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, although the protagonist survives this. Sans then uses his "special attack", which ends up being nothing (and thus never ends 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 box so that they can select the FIGHT option. Sans dodges the first attack, but the second attack (unprovoked by the protagonist) hits. He appears to bleed from his wound, though it's speculated that the "blood" is truly ketchup, since Sans is known to drink entire ketchup bottles. Sans reminds the protagonist that he warned them before getting up, and weakly walking off-screen. Sans's death grants the player enough EXP to reach LV 20.

In Battle

 * See Sans/In Battle

Frisk
Sans is the first monster the protagonist meets outside The Ruins. When he first meets the protagonist in Snowdin, Sans is friendly to them, regardless of the play style they are following. He plays jokes on them, using a "whoopee cushion in hand" trick when they first meet. He is able to tell whether the protagonist has experienced the events of the game before, and his attitude toward the protagonist changes drastically depending on how merciful, or otherwise, they are during the current playthrough. Sans only battles the protagonist at the end of a Genocide Route, where he believes that the existence of the world's timelines are in danger.

If the player dines with Sans in the MTT Resort, then Sans tells the protagonist that had he not promised to protect them, they would be "dead where they stand", implying that he would've killed them himself.

Papyrus
Sans cares for and admires his brother. He reads Papyrus bedtime stories, and even gifted him action figures. Nonetheless, he likes to prank and joke with his brother- which is typical of him. Sans is worried about other people taking advantage of Papyrus' innocence; he assumes that Papyrus talking about a flower talking to him is actually someone using an echo flower. If the player kills Papyrus, then Sans disappears until the final corridor, where (on a Neutral Run) he harshly judges the player for this. On various neutral endings, Sans is also afraid to tell Papyrus about the people you have killed, so he lies about them going on a vacation.

Toriel
Toriel and Sans are close friends, sharing a love of bad jokes. He never sees her in person until at the end of a True Pacifist run. While not being one to keep promises, in all runs except the Genocide Run Sans complies with her request to not harm any human that passed through the door exiting the ruins. Toriel keeps record of Sans's knock-knock jokes in her diary.

If the protagonist reaches him at the end of the Genocide Run, he indirectly apologizes to Toriel, as he is forced to break his promise in order to stop the player.

Flowey
Sans doesn't seem to know much about Flowey himself beyond that he's the talking flower that appears before Papyrus; although " talking flower " and " echo flower " are in different colors when Sans mentions it and then claims somebody's using an echo flower for a prank.

On the other hand, Flowey states in one of the Neutral Route Endings that he tried to experiment with Sans using his SAVE ability. However, Sans "caused more than [Flowey's] fair share of resets" as if Sans was just about the only thing capable of stopping him, much the same as it is for the player on the Genocide Route. Flowey also calls Sans a "Smiley Trashbag."

Trivia

 * Sans is shown wearing sneakers in his Steam Trading Card. However, he is shown wearing slippers on the official Undertale brand "Mercy" T-Shirt.
 * His name refers to the typeface, Comic Sans, which is a reference to the webcomic, Helvetica, a webcomic about a skeleton named after a font.
 * In addition to talking in the Comic Sans font, Sans himself is a comic and loves to make bad jokes. Sans is also a performer in MTT Resort's restaurant, hinting he may be a skilled comedian.
 * At certain points in the game, Sans will drop his font and will the game's font instead. When he is talking this way, he is usually at his most serious and his dialogue cannot be skipped and is not accompanied by his voice beeps.
 * During Sans' boss fight in the Genocide Route, when Sans falls asleep, the font used for his Z's are in the Aster font, which could indicate another connection to W. D. Gaster.
 * If you attempt to name the fallen human "Sans", the response becomes "nope." and prevents you from using the name.
 * He, along with Papyrus, make a brief appearance at the end of Undertale Demo if the protagonist does a perfect pacifist playthough.
 * Sans may call the protagonist to ask if their fridge is running.
 * Sans can be found running an illegal hot dog stand in Hotland selling Hot Dogs and Hot Cats. If the protagonist buys a hot dog when they can afford one but have no room in the inventory, Sans will begin to place the hot dogs on their head. Sans can only stack twenty-nine hot dogs on the players head.
 * Many things can be found throughout the game that indicate that Sans might formerly be from a scientific background such as the quantum physics book, workshop, and broken machine found in Papyrus and Sans's House. Papyrus, in a phone call on the first floor of the Lab without Undyne, will mention that he loves science fiction. There's also an implication that Sans and Alphys know each other when talking to her at the end of a True Pacifist Route.
 * Accessing Sans's Room reveals that his bed is in a state too poor to sleep in, his sheets rolled up in a pile on his mattress and his mattress is uncovered. This may explain they fact why Sans is sleepy in certain parts of the game. He also has a treadmill, which he pranks the protagonist with but may also explain why his attacks are fast during the fight against him on a Genocide Route.
 * He is among one of the three characters who will try to convice the protagonist to stop playing the game, the others being Flowey and the fallen human.
 * Sans seems to have the ability to teleport. He refers to the ability as a "shortcut".
 * In Snowdin Forest, on the path to the cavern containing the Mysterious Door where Gyftrot is encountered, he seems to teleport from one side of the screen to the other and jokingly asks the protagonist if they're following him.
 * After the "Gauntlet of Deadly Terror" puzzle in Snowdin Forest and on a Genocide Route, he teleports right after warning the protagonist they will potentially have a bad time if they decide to stay on this route.
 * In a cell phone conversation with Papyrus at the ice puzzle in Snowdin Forest, Papyrus mentions that he just jumps across the gap instead of solving the puzzle, he then mentions that Sans doesn't solve the puzzle either and just knows a way on how to get across.
 * At Sans's sentry station in Waterfall, he asks you to take a shortcut with him to Grillby's. This is repeated in front of MTT Resort when he takes you to the restaurant at the resort.
 * Sans loves to drink ketchup. If the protagonist declines the bottle of ketchup when Sans takes you to Grillby's, he does drinks the entire bottle of ketchup in front of him. Condiment bottles can also be seen in Sans's sentry station in Snowdin Forest. This has led people to believe that Sans is 'bleeding' ketchup from his wounds in the fight against him.
 * The sprites for the weapon he uses in the boss fight against him on the Genocide Route are labeled "gasterblaster" which is most likely another reference to W. D. Gaster.
 * There is evidence to support the idea that Sans is left-handed.
 * Sans greets you with a handshake using his left hand.
 * At Grillby's, if the protagonist refuses the ketchup, he holds and drinks the bottle with his left hand.
 * When riding the motorcycle in the True Pacifist Ending Credits, he uses only his left hand to control the motorcycle, while keeping his right hand in his jacket.
 * He notably uses his left hand when using magic in his boss fight on the Genocide Route.
 * It's Raining Somewhere Else is labeled "mus_Sansdate" in the games files, implicating that a date with Sans may have been planned for in the game or that the dinner with him was the 'date'.
 * Sans seems to know if the player has achieved an impossible ending in the Neutral Route's phone call and will call them a dirty hacker. Given that this also counts as an error handling message, he is aware of when the game's code suffers bugs as well.
 * Encountering Sans for the first time, then reloading a save before the encounter or resetting the game, will cause the protagonist to shake his hand after he says "Human." Sans will quickly notice this and calls this weird.
 * According to one of Toby Fox's older tweets, in the Japanese version of Undertale, Papyrus would use "aniki" when referring/talking to Sans. Aniki is a honorable term exclusively used for older brothers, meaning that canonically Sans is the older brother.
 * Despite being a skeleton, Sans's hand doesn't resemble a skeleton's. This could be, however, because he is wearing a glove, as his hometown's climate is cold.
 * After killing Sans in the Genocide Route, his death is not added to the protagonist's kill count.