Sans

1. Moving to Snowdin. Before the events of Undertale, Sans moved to the town of Snowdin with his younger brother, Papyrus. The reasons and location of their previous residence are unknown.
2. Relationship with Papyrus. Sans is Papyrus's older brother. Despite their differences in personality (Papyrus is energetic and idealistic, Sans is lazy and cynical), they have a warm and supportive relationship. Papyrus dreams of becoming a royal guard and persuades Sans to help him catch people who have fallen into the Underground, although Sans himself is skeptical of the idea.
3. Name. Sans's name refers to the Comic Sans font used for his dialogue boxes. This is part of a general concept: the brothers' names are related to fonts (Papyrus stands for Papyrus).
   Key episodes before the game's plot:
4. Meeting a Mysterious Woman. At the MTT restaurant, Sans tells the player about a woman he met behind a mysterious door in Snowdin. They became friends over their shared love of puns. Before leaving, the woman made Sans promise not to harm anyone trapped in the Dungeon. If Sans hadn't kept his word, the player, in his words, would have been "dead right where he stood." The woman's identity is not revealed, but her influence on Sans is clear: he strives to keep this promise.
5. Work. Sans probably worked for Undyne (the captain of the royal guard) for a while, but due to laziness, he performed minimal duties.

Before the events of the game, Sans had already formed as:

1. Lazy and relaxed. He avoids unnecessary work, jokes, and teases others.
2. Observant and perceptive. Sans notices details that others miss and draws conclusions about people's motives.
3. True to his commitments. Despite his outward casualness, he takes his promises seriously (as seen in the story with the woman).
4. Concealing the Depths. Behind the joker's mask lies an understanding of the tragedy of the situation in the Dungeon and an awareness of the consequences of the Player's actions.

1. Origin. Sans and Papyrus' origins remain a mystery. It's unknown where they came from in Snowdin or how they became skeletons—this is intentionally not explained in the game.
2. Awareness of the "game-like" nature of the world. Sans demonstrates hints of an understanding that the world of Undertale is governed by certain rules (saving, resetting), but his backstory doesn't reveal how or when he realized this.

Main features of appearance:

1. Appearance: a relatively short and "big-boned" skeleton with a characteristic appearance with mitten-like hands.
2. Height and build. Sans is noticeably shorter than his brother Papyrus, and he has a noticeable belly.
3. Face. He is always depicted with a wide, toothy smile. Bags are visible under his eyes, accentuating his relaxed and slightly tired appearance.
4. Eyes. In normal condition, the eye sockets are filled with white pupils, which disappear when Sans becomes serious or angry. When using telekinesis, the iris in his left eye appears, flashing yellow and blue.
   Cloth:
5. Outerwear. Wears a blue sweatshirt or jacket with a gray hood. It is mentioned that it is always unbuttoned.
6. Underwear. A white T-shirt or sweatshirt is visible under the sweatshirt.
7. Shorts. Black with white stripes on the sides.
8. Shoes. Pink slippers.

1. "Shortcuts." Sans can instantly travel great distances, allowing him to quickly traverse locations and create the impression of being in several places at once. Doggo confirms this ability, noting that Sans appears nearby without any indication of approaching.
2. Teleportation. He can teleport not only himself but also objects and other creatures. This helps in combat: dodging attacks, moving an enemy into the area of ​​a prepared attack, restraining an enemy by returning them to their original position.
3. Knowledge of Timelines and Saves. Sans is aware of resets and timelines (Flowey mentions having to reset the game numerous times because of Sans). This gives him a number of advantages: he understands when the protagonist is behaving unusually (for example, due to previous attempts), and can "read" the Player's death count and experience level (EL) from their facial expressions.
4. SOUL Manipulation (Blue Mode). Like his brother Papyrus, Sans can color his opponent's SOUL blue by altering the gravity around it. However, Sans is much more proficient in this ability: he can make opponents move along walls or ceilings, or throw them by manipulating their SOUL.
5. Gaster Blasters. A weapon invented by V.D. Gaster. These are skull-shaped devices that fire laser beams. Sans can summon dozens of these blasters simultaneously. Their features include varying beam sizes and strengths, some blasters firing multiple times in a row, and during his final attack, Sans uses multiple blasters firing in a circle.
6. Dice Attacks. Sans throws a multitude of dice, creating complex evasive trajectories: regular dice require jumping over or going around, while blue dice prevent movement but deal no damage if standing still.

8. Karmic Retribution (KARMA). A unique ability that compensates for Sans's low base attack (1 damage): each successful attack turns a portion of the enemy's health purple. This purple damage gradually depletes the target and does not disappear completely. Healing is practically useless: even after a full recovery, the purple area continues to slowly drain health.
9. Attack Dodging. Sans is able to dodge almost any attack, even if it's aimed directly at him.

Character and behavioral traits that influence abilities:

1. Laziness. Sans won't fight unless he deems it necessary (for example, on the NEUTRAL or PACIFIST path, he doesn't attack the Player). On the GENOCIDE path, he's forced to break his promise to protect people in order to stop a mass murderer.
2. Endurance. Despite his immense strength, Sans tires quickly. By the end of a fight, he shows signs of fatigue, and he can even fall asleep during the fight.
3. Keeping promises. Sans tries to keep his word. For example, he promised Toriel to protect the people who fell into the Dungeon—this explains his behavior in the early stages of the game.
4. Awareness of game mechanics. Sans understands the rules of the Undertale world, including saving and reloading. This makes him one of the most insightful characters in the game.
5. Humor and trolling. Even in battle, Sans jokes and teases his opponent, which can disorient the Player.

1. Low base attack and defense. Sans has only 1 attack and 1 defense. His strength is built on exhausting his opponent through KARMA and complex attack patterns.
2. Limited stamina. Prolonged combat quickly exhausts Sans, which can lead to unconsciousness.
3. Conditional Dependence. Sans won't fight seriously until he sees a real threat. This changes on the GENOCIDE route, but even then he apologizes to Toriel for breaking his promise.

1. Physical Limitations: Low base attack (1 damage) and defense (1). His strength is built not on direct strikes, but on exhausting the opponent through KARMA and complex attack patterns. He tires quickly. A long battle quickly exhausts Sans. By the end of the battle, he may fall asleep or lose consciousness right during the fight. Condition-dependent. He won't fight seriously until he sees a real threat. On the PACIFIST and NEUTRAL paths, he won't attack the player.
2. Moral and Emotional Limitations: Loyalty to Promises. Sans strives to keep his word, which can limit his actions. For example, he sticks to his promise to protect people (made to Toriel and the mysterious woman) for a long time, even when it becomes dangerous. He cares for his loved ones. He prioritizes the safety of Papyrus and his friends. On the Genocide Route, he is forced to break his promise to protect people in order to stop a mass murderer, but he does so with regret (he mentally apologizes to Toriel).
   Empathy. Believes in the good in others and believes that bad behavior is often caused by difficulties in life. This position can make them vulnerable to deception or manipulation.
3. Limitations: Awareness of timelines does not grant complete control. Sans understands that the world obeys the rules of saving and resetting, but he himself cannot save. He does not remember events after a reset, although he notices anomalies in the Player's behavior. Energy consumption. Using shortcuts, teleportation, and gaster blasters requires resources. The longer the battle, the weaker Sans becomes. Vulnerability to unexpected actions. Despite his insight, Sans can be caught off guard if the enemy acts outside of expected patterns (for example, abruptly changes strategy in battle).

4. Behavioral factors: Laziness. Often avoids making an effort, which can work against them in critical situations. An ironic communication style. Jokes and teasing sometimes mask the seriousness of a threat, causing the enemy to underestimate their capabilities until the last moment.

1. Laziness and relaxation. Sans constantly emphasizes that he doesn't like to exert himself: he sleeps on the job, avoids unnecessary effort, and often looks for ways to simplify tasks. However, his laziness is partly due to his awareness of the cyclical nature of the world (due to saving and resetting): he understands that any work can be "erased" by resetting the game.
2. Humor and trolling. He's known for his off-color jokes and puns, which often irritate those around him—especially Papyrus. He jokes even in tense situations, which can be disconcerting.
3. Kindness and empathy. Believes in the good in others and believes that bad behavior is often caused by life's difficulties. Seeks to resolve problems without vengeance, through understanding and protecting loved ones.
4. Faithful to promises. If he makes a promise, he tries to keep it, even if it's inconvenient. For example, he promised Toriel to protect the people who fell into the Dungeon—and he has maintained this principle for a long time.
5. Insight. Notices details that others miss. Can "read" a person's state and intentions from their facial expressions, and also recognizes anomalies in the protagonist's behavior (related to reboots).
6. Awareness of game mechanics. He is one of the few characters who is aware of the existence of saves and timelines. This makes him particularly attentive to any oddities in the Player's actions.
7. Caring. Despite his outwardly careless appearance, he genuinely cares for his brother Papyrus and his friends. He's willing to go to great lengths to protect them.
8. Pragmatism. On the GENOCIDE path, Sans is forced to break his promise to protect people in order to stop a mass murderer. He does this with regret (even mentally apologizing to Toriel), but considers it the lesser evil.

1. Casual and informal. Speaks in a relaxed, often ironic manner. Uses colloquialisms and slang, creating the feeling of a friendly conversation.
2. Dialogue font. His lines are displayed in Comic Sans (lowercase), emphasizing the informality and humorous delivery. In rare, serious or threatening moments, the font switches to standard, signaling a change in tone.
3. Puns and jokes. He constantly makes lame jokes and puns about bones, skeletons, and science. Even in combat, he can make ironic comments, confusing his opponents.
4. Sarcasm and teasing. He enjoys making fun of his interlocutors, sometimes with a touch of sarcasm. For example, he comments on the Player's actions with mocking approval or feigned surprise.
5. Brevity and directness. Prefers short phrases and avoids long monologues. Often uses hints instead of direct explanations.
6. Shifts between a playful and serious tone. At critical moments (especially on the GENOCIDE path), he suddenly becomes collected and stern. His speech loses its playfulness, and clear warnings and direct assessments of the Player's actions appear.
7. Using hints. Sometimes he gives hints or warnings indirectly, through jokes or ambiguous phrases. For example, on the PACIFIST path, he might hint at the consequences of a choice without revealing details.
8. Emotional restraint. Even in tense situations, Sans rarely raises his voice or openly displays strong emotions. His seriousness is conveyed through changes in intonation and speech style, rather than through shouting or threats.

1. Origin and Family: Sans is Papyrus's older brother. Before the events of Undertale, Sans and Papyrus moved to the town of Snowdin.
   The brothers' origins (previous place of residence, history of transformation into skeletons) are not revealed in the game.
   The name refers to the Comic Sans font, which is used to display his lines in the game.
2. Role in the Dungeon: Helps Papyrus "catch" people who have fallen into the Dungeon, though he is skeptical of the idea. For a time, he worked for Undyne (the captain of the royal guard), but performed minimal duties due to laziness.
3. Key backstory moments: Met a mysterious woman behind a mysterious door in Snowdin. They became friends over their shared love of puns.
   He promised her not to harm anyone trapped in the Dungeon. This commitment greatly influences his behavior in the game.

1. Sleep and rest. Sans loves to sleep—he can doze off at any moment, even during work or battle. He often says he'd rather rest than work.
2. Jokes and puns. He loves cheesy jokes, especially about bones, skeletons, and science. He enjoys playing pranks and teasing others (though Papyrus usually doesn't appreciate his humor).
3. Hot dogs. This is his favorite food. He often goes to Grillby's and, according to rumors, even works with hot dogs.
4. Communication and friendship. He values ​​his loved ones and is willing to help them. He enjoys spending time with friends, chatting, and joking. He genuinely cares for his brother Papyrus and tries to support him.
5. Puns with others. In the backstory, Sans befriended a mysterious woman over their shared love of puns—an important social element for him.
6. An easy lifestyle. Prefers to take it easy, avoiding unnecessary work and difficult situations. His motto is close to "why do today what you can put off until tomorrow."
7. Observing others. He's interested in observing the behavior of people and monsters, noticing details and drawing conclusions. This is partly due to his understanding of the world's mechanics (saving, resetting).
8. Drinks from Grillby's. He often visits Grillby's, where he enjoys various drinks and socializing. It's his place to relax and socialize.

1. Stress and work. Sans hates serious work and commitments. He avoids tasks that require effort or responsibility at all costs.
2. Making promises. He doesn't like making promises because it places limitations on him. In the game, he says outright, "That's why I never make promises"—especially after he was forced to break his promise to protect people during the GENOCIDE.
3. Cruelty and senseless violence. Sans believes that killing without reason is wrong. He tries to solve problems without revenge and believes that people can change.
4. When his loved ones are hurt. Sans takes it extremely negatively when someone harms Papyrus or his other friends. On the Genocide route, he stands up for the Dungeon precisely because the Player is killing everyone.
5. Serious conflicts. Prefers to defuse the situation with a joke rather than engage in open conflict. Hates escalating violence and tries to avoid situations that require force.
6. When his jokes aren't understood. While he continues to joke around regardless, he likely gets upset when his humor is ignored or criticized (as Papyrus often does).
7. Long and tedious battles. Sans tires quickly. He doesn't like wasting energy on protracted battles – he prefers to finish things quickly or avoid combat altogether.
8. Hypocrisy and double standards. He values ​​honesty and notices insincerity. If someone acts contrary to their words or principles, Sans notices it and may react with irony or condemnation.