Sans (/ˈsænz/ SANZ) is the brother of Papyrus and a major character in Undertale. He first appears in the forest after the protagonist exits the Ruins. He serves as a supporting character in a Neutral and True Pacifist Route and as the final boss and heroic antagonist in a Genocide Route.
Sans is a short skeleton with a dimpled smile and large orbits. He wears an unzipped blue hoodie, a white t-shirt/sweater, black shorts with white stripes, and a pair of sneakers/slippers.He has white pupils that disappear when he is serious or angry. When Sans uses his magical psychokinesis, his left eye flashes light blue and yellow, the colors for patience and justice, and his right pupil disappears.
Sans is laid back, often sleeping on the job and taking breaks. His laziness is a combination of fatalism and apathy. He wonders if his indolence stems from his knowledge that any progress he makes will be erased when the timeline resets. Conversely, he suggests that this knowledge could be "a poor excuse for being lazy."
Though Sans is usually agreeable, he becomes eerily serious at particular moments. He is also observant; Sans reads the protagonist's expressions and can often tell when they have already done certain tasks. He enjoys making bad, skeleton-related puns, although the fact that he performs at MTT Resort hints that he may be a talented comedian. He enjoys science fiction and loves to drink ketchup. He also hates making promises.
Sans may have a scientific background. Evidence includes the quantum physics book ( in a joke book ), workshop, his relationship to Alphys, affinity for science, and his timeline research.
Sans can quickly travel or teleport using what he calls "shortcuts."
In combat, he uses "Gaster Blasters," devices that resemble a dog's skull, to shoot a kind of concencrated laser beam that deals massive damage. Sans excels in combat and fights with unique abilities that include: Karmic Retribution, changing the effect of gravity on the SOUL, dodging attacks and attacking the protagonist in the selection menus. His magic reacts to EXP; Karmic Retribution would presumably be weaker if the protagonist had little EXP.
Because of his "research," he has knowledge of timelines and the SAVE function. However, he does not retain his memories when the protagonist loads a SAVE, and he cannot use the SAVE function. His awareness of time travel makes him scrupulous, and he recognizes when the protagonist is behaving unusually. Sans reads the protagonist's expression and determines if they have experienced events before and are repeating them. He also knows how much EXP the protagonist has and comments on it when judging them.
Sans also plays the trombone, though he is only seen playing it once. Papyrus finds his "incidental music" annoying, implying that he has played many times before.
Like other characters, Sans is aware of when the game's code suffers bugs and calls the protagonist a "dirty hacker" if they achieve an impossible ending of a Neutral Route.
Sans introduces himself to the protagonist in Snowdin Forest after he initially appears as a silhouette. He explains that he has no interest in capturing humans, but that his brother, Papyrus, does. Then, Sans hides the protagonist behind a lamp whose shape is identical to the protagonist's. Papyrus rushes onscreen, and the brothers discuss Sans's laziness and the importance of puzzle upkeep. Sans appears multiple times throughout Snowdin Forest, observing and commentating on the puzzles but not engaging in any japery, except for the word search.
Before Papyrus's battle, Sans is absent in Snowdin Town. He appears briefly to play trombone during the date/hangout with Papyrus but does not appear again until the Last Corridor if the protagonist kills Papyrus.
After entering Waterfall, Sans is found manning a sentry station and asks the protagonist if they want to take a break with him. If the protagonist agrees, he takes them to Grillby's via "shortcut." The patrons warmly greet Sans, and he proceeds to treat the protagonist to a burger or fries. After some dialogue, a spotlight falls on him and the protagonist; time appears to stop as Sans tells the protagonist that a flower has been talking to Papyrus. Sans believes that someone is tricking Papyrus with an Echo Flower when the flower in question is Flowey. Sans can be seen again in Waterfall and pranks the protagonist with a red-eye telescope.
The protagonist passes him sleeping at a sentry post in Hotland when fleeing from Undyne. Undyne notices him sleeping and berates him mid-chase.
Later, Sans sells Hot Dogs in Hotland for 300G. If the protagonist attempts to buy a hot dog when their inventory is full, he stacks a maximum of 30 hot dogs on their head for free. These "head dogs" vanish when the protagonist enters the next room.
Further on, Sans waits outside of MTT Resort and asks the protagonist if they want to grab a bite to eat. He escorts the protagonist inside via "shortcut" and talks about a woman he has befriended that shares his affinity for puns. He tells the protagonist that this woman made him promise to protect any human that left the Ruins and that, if she had not said anything, the protagonist would be "dead where [he] stands." He dismisses this as a joke immediately and says that he has done a great job protecting the protagonist. If the protagonist has not died before, Sans takes credit for their success. If the protagonist has died, Sans questions the validity of his statement. Before leaving, he tells the protagonist to take care of themself because someone really cares about them.
The protagonist encounters Sans for the last time in the Last Corridor. He explains that EXP and LOVE are acronyms - "EXecution Points" and "Level Of ViolencE" and judges the protagonist for his current EXP.
If the protagonist gained no EXP, Sans skips his judgment, instead praising the protagonist for embracing compassion and actively choosing to be merciful to the monsters throughout their journey despite nearly everyone wants to kill him. He reinforces the idea that the protagonist's actions shall decide the fate of the world in one of two ways: the protagonist lets Asgore take their SOUL and allow the monsters to break the Barrier or they take Asgore's SOUL to escape the Barrier themselves. Sans concludes that the protagonist now has enough determination and believes that they can do the right thing before leaving.
After the protagonist defeats Photoshop Flowey, Sans calls and informs him of the events that transpired after his departure. The content of this phone call varies depending on the protagonist's actions; a list of the endings that Sans describes is on the Neutral Route page.
True Pacifist Route
Sans is absent from the Last Corridor in a True Pacifist Route. There is also no SAVE point upon entering the corridor. He appears during the pre-Asriel cutscene and meets Toriel face-to-face for the first time. Flowey binds Sans and the protagonist's other friends. However, the protagonist's friends protect them from Flowey's attacks before Flowey absorbs 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 because Toriel's thumbs are too big for the phone buttons. When 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 rides a tricycle on a highway, while his brother races alongside him in a car. Papyrus seems irritated when his brother somehow overtakes him.
Sans stalks and introduces himself to the protagonist as usual but requests that they continue pretending to be a human. He does not comment on the protagonist turning around before he asks them to. Sans goes along with Papyrus's japery and does not appear as an NPC as he does on other routes. After the protagonist crosses the bridge before Snowdin Town, Sans warns them not to fight his brother or else they will "have a bad time." He then disappears and is absent until the Last Corridor.
If the protagonist aborts a Genocide Route by sparing Papyrus, Sans reappears at the Waterfall sentry station and tells the protagonist he respects them for doing that. He continues to appear as if on a Neutral Route but does not take the protagonist to Grillby's since there is no one left in Snowdin. Alternatively, Sans follows/stalks the protagonist if they kill Papyrus.
The protagonist encounters Sans in the Last Corridor for his battle.
After defeating Sans, the protagonist's EXP is set to 99999, granting him LV 20. Sans notices if the protagonist has killed him before and is re-fighting him.
Sans does not count as a kill in the Stats menu, and the game does not record whether or not he is killed.
JK ( AKA Protagonist )
Sans's attitude towards the protagonist depends on their actions, though he usually enjoys pranking him and occasionally hanging out with them unless they kill Papyrus. Near the end of a Neutral Route, he judges them on their EXP. At the end of the True Pacifist Route, Sans considers them a good friend.
Sans initially considers the protagonist to be an "anomaly"( Genocide Chara ); his intentions of befriending them were in hopes that they would stop resetting the timeline.However, he also says that the protagonist did not die after their initial encounter because of his promise to Toriel. This may imply he would have killed the protagonist or that he protectedhim from life-threatening harm after their first encounter.
Sans cares for and admires his brother. He reads him bedtime stories and gives him presents under the identity of Santa. Nonetheless, Sans likes to mess with Papyrus, sending him bad puns on the UnderNet. He also leaves a dirty sock in their living room for Papyrus to fuss over.
Sans worries about others hurting Papyrus or taking advantage of him. In some Neutral Endings, Sans is afraid to tell Papyrus about other characters' deaths, so he lies about them going on a vacation.
Toriel and Sans share a love of bad jokes and are friends even though they never see each other face-to-face until the epilogue, the Family Ending, or the Exiled Queen Ending. Before the protagonist's arrival, Sans and Toriel shared jokes through the door to the Ruins.
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 is alive, the brothers visit Toriel often, play board games together, and sometimes convince Toriel to leave the Ruins.
While not being one to make promises, Sans complies with Toriel's request to watch over and protect any human that exits the Ruins. At the end of a Genocide Route, he indirectly apologizes to her, as he is forced to break his promise to stop the protagonist.
Though there is evidence that Sans and Alphys have a relationship, Sans only alludes to this in the epilogue.
It is also noteworthy that if Papyrus and Undyne are called just before entering the Laboratory, Sans appears in the call and state that there may be dogs inside the lab. This hints that he knows about the true lab since Endogeny, an amalgamate containing several dogs can be found there.
A few things hint at a connection between Sans and W. D. Gaster. Evidence includes the blueprints and veiled machine found in his workshop, the sprites used for his skull-like laser guns (labeled gasterblaster in the game files), and his unexplained scientific research on the "anomaly" and timelines. Sans and Papyrus are named after a font, as well as W.D Gaster, so it is believed they are related.