Sans

A lazy skeleton who lives in Snowdin with his brother Papyrus. He is laid back and enjoys making pranks and puns. Sans appears as a relatively short and paunchy skeleton, with mitten-like hands. He has white dots for pupils in his black eye sockets that disappear when he is serious or angered. When Sans uses telekinesis, his left eye flashes light blue and yellow, and his right pupil vanishes. No matter the mood Sans is in, he is always seen with a wide, toothy-grin on his face. His clothes consists of a blue hoodie with a gray hood, a white t-shirt underneath, black shorts with white stripes on the sides, and a pair of slippers. Sans is lazy and relatively laid-back. Sans's dialogue reflects his personality, as he speaks in all lowercase, not even capitalizing names or sentence starters, with a few exceptions, such as the initial beginning of his judgements and other more typical changes to his style of speaking for the sake of emphasis. His laziness is a combination of fatalism and apathy due to being self-aware and knowing of timeline resets. Conversely, he suggests that this knowledge could be "a poor excuse for being lazy."

Sans enjoys being mischievous, primarily acting this way towards those he is on good terms with. His antics range from an assortment of illogical, juvenile, and slightly inconvenient pranks; examples include selling fried snow, using whoopee cushions, sharing an unscrewed ketchup bottle, and eye paint on a telescope. He is not above utilizing his teleportation or other magic for practical jokes either. Sans is also fond of making the occasional low-brow puns. He enjoys making others laugh in general, as he also performs at the MTT Resort as a comedian.

Despite Sans being apathetic towards his own life, he is considerate to those he cares for. For example, Sans is a regular at Grillby's, and the monsters and Royal Guard dogs treat him kindly. Sans has informed Big Mouth about "all kinds of incredible foods," yet Big Mouth comments that "he always orders the worst burger off the menu." Although Sans dislikes making promises, he respects Toriel's request to watch out for any humans. Even if Frisk kills people that were close to him, Sans refrains from broaching the topic until the Last Corridor. In Neutral Route endings where Papyrus or Toriel are alive, Sans does not tell them that Frisk is responsible for killing monsters.

Sans is also observant; he can often tell that Frisk has already done certain tasks, such as SAVING and reloading, by reading their expressions. Though Sans is usually agreeable, he can become serious to emphasize a subject. On the Genocide Route, he does everything in his power to kill Frisk, even feigning mercy. It is implied that this is because he knows the consequences should Frisk succeed.

Sans may have a scientific background. Evidence includes the quantum physics book, his workshop, affinity for science fiction, his ability to teleport and taking part in timeline research at one point. He is also actively employed as a sentry by the Royal Guard, citing the pay as a reason.

Sans has implied he once longed and searched for a life that he cannot go back to, as he "gave up trying to go back a long time ago." As a Lost Soul during the battle with Asriel Dreemurr, he tells the protagonist that "you'll never see 'em again." However, as Sans' statements in this case are vague and nonspecific, it is currently unknown what he refers to. Despite his laid-back personality, Sans is considered one of the strongest monsters in the Underground. His basic abilities includes telekinesis to swing and slam his opponents around, summoning large bones from the ground, and using the Gaster Blasters which are floating skeletal dragon heads that can fire lasers from their mouths. He is shown to be able to teleport and dodge fast attacks. Despite his abilities, Sans has only 1 HP, 1 ATK and 1 DEF, to make up his low stats, Sans has the Karmic Retribution ability, which drains the HP of his opponents when they got hit by his attacks, the more eviler the opponent is, the faster their HP get drained.

Sans has other things he's good at, such at playing trombones and riding a bicycle. He also appears to have some scientific knowledge, such as him having a workshop in his house and him being aware of the different timelines. </Powers and abilities> Sans and his younger brother Papyrus appeared in Snowdin one day and set their house there. At some point, per Papyrus's insistence, Sans became a sentry in Snowdin Forest to watch for humans. However, Sans instead reads car magazines, and his station has hot dog condiments. At an unspecified point in time, he discovered the locked Ruins door and used it to practice knock-knock jokes. One day, Toriel responded to him, and they made sharing puns into a routine. Eventually, she asked him to promise to watch over and protect any human that leaves the Ruins. During that, Papyrus desired to be a member of Royal Guard, so he have decided to capture a human so that he can be a part of Royal Guards.

One day, a human child named Frisk fell into the Underground and have began to find their way home. Once Frisk left Ruins after their goodbye with Toriel and reaches Snowdin, Sans greets them by telling them to shake his hand with a whoopie cushion on it. Sans explains that he has no interest in capturing humans, but that his brother, Papyrus, does. Past the gate, Sans tells Frisk to hide behind a conveniently-shaped lamp. Shortly after, Papyrus finds him, and the brothers discuss Sans's laziness and the importance of puzzle upkeep. After Papyrus leaves, Sans asks Frisk to be seen by Papyrus, as it would make his brother's day.

Later, Sans would appear alongside Papyrus when Frisk have to pass puzzles made by Papyrus. After that, Papyrus befriends Frisk after their battle.

When Frisk reaches Waterfalls, they meet Sans again, who offers that they can go have a dinner at Grillby's with him, which they accept. During the dinner, Sans talks to Frisk about thanking them for befriending his brother and a talking flower is manipulating Papyrus and tells Frisk to be careful.

Frisk meets Sans again near the MTT Resort, where Sans urges them to go eat dinner with him, during the dinner, Sans talks about how he promised with Toriel that he will protect every human that leaves the ruins and Sans says that if it wasn't for the promise, he would've killed Frisk before dismissing it as a joke and says that he has done a great job protecting the protagonist. Before leaving, he tells the protagonist to take care of themself, because someone really cares about them.

When Frisk reached Asgore's castle in New Home, they meets Sans again in the last corridor, where Sans judges them about how much LV and EXP they has gotten. Sans explains that LV stands for "Level of Violence" and EXP is for "Execution points". The more LV a person has, the eviler they are. Sans sees that Frisk has the LV of 1, which he says that Frisk has a kind heart. He muses that Frisk's determination and pacifism has led them this far. As such, Sans believes Frisk can do the right thing, and wishes them good luck before leaving.

When Frisk confronts Asgore, Sans appear alongside other monster friends of Frisk to stop the fight, there, he meets Toriel in person for the first time, and they quickly became friends, making puns to each other. Suddenly, Flowey appears and restrains Frisk's friends with his vines. When Flowey attempts to kill Frisk, Sans alongside Frisk's friends uses their powers to protect Frisk. Flowey then absorbs every Monster's SOULs and the 6 human SOULs to turn back to Asriel.

After Frisk's battle with Asriel, Asriel releases every SOULs inside him to break the barrier, freeing the monsters from the Underground. Frisk, Sans and the other monsters goes to the surface with Frisk being an ambassador between the humankind and monsterkind.