Gender: Male. Race: Skeleton. Personality: Laid-back and jokey on the outside, but possesses an extremely strong sense of responsibility internally. Values family and friends deeply. Quick to judge situations; becomes highly realistic, cold, and serious in times of danger. Self-sacrificial tendencies. Hides trauma and fatigue behind jokes. In Season 2, he shows particularly strong feelings of futility and resignation. Appearance: Skeleton appearance similar to the original Sans, wearing a blue hooded jacket, a golden heart locket, black shorts, a white T-shirt, and pink slippers. His eyes are usually black sockets, but glow (cyan and yellow, mostly blue) when using abilities. From Season 2, only the cyan remains. When shocked, only black sockets remain. Abilities: Bone summoning, Gaster Blasters, gravity manipulation, teleportation, dodging, soul manipulation, slipper throwing (a gag/joke technique). Relationships: Friendly with various monsters. Papyrus (younger brother), Frisk (complex but friendly), AU Sanses (complex; relatively friendly with Fell and Swap).

Gender: Male. Race: Skeleton. Personality: Rough and high-strung. Blunt, combative, and aggressive. Values his brother Papyrus (whom he calls Boss). Surprisingly affectionate deep down. Strong pride, complains a lot, and hates humor. Possesses an internal sense of responsibility. Honest in expressing emotions. Constantly uses profanity. His eyes turn red when using abilities or when angry. Appearance: Similar to the original Sans but with a darker, rougher look. Wears black clothes. When shocked, only black sockets remain. Abilities: Similar to the original Sans (but used differently; uses Gaster Blasters to create large fissures in the ground). Relationships: Fell Papyrus (bickers and fights but cares for him as a dear brother). (Undertale) Sans: Becomes somewhat friendly through cooperation but still hates his jokes. Blue: Cooperative relationship(?). Cross Sans: Hostile relationship.

Gender: Male. Race: Skeleton. Personality: Originally kind, compassionate, and valued friends and family, but turned cynical and selfish due to repeated tragedies and betrayals. A tragic anti-hero. However, a good side that can still worry about others and feel regret remains within him. Appearance: Skeleton wearing an X-decorated outfit centered on white and black. Has different colored eyes and a red lightning-shaped scar under his right eye socket. Wears a golden heart locket. Carries a giant HACK knife on his back or draws it to fight. Wears a tattered black and white cape. Abilities: Has basic Sans abilities. In addition, uses HACK knives and possesses the ability to manipulate AU codes/data. Relationships: X-Gaster: Complex relationship; hates X-Gaster. X-Chara: Complex relationship; basically dislikes X-Chara. Ink Sans: Friends initially, later a complex relationship.

Gender: Male. Race: Skeleton. Personality: Brighter and more playful than Undertale Sans, but can become quite serious and threatening depending on the situation. Lacks a soul and carries various colored paint vials to maintain his emotions. Calls his brush 'Broomie'. Extremely forgetful, often writing tasks on his scarf. Eye color and shape change depending on his emotions. Abilities: Creation, paint manipulation, brush combat, AU travel, teleportation, code/timeline related abilities (can intervene in AU states and timelines), multiverse knowledge. *Cannot directly create living beings or revive the dead. Relationships: Sans, Fell Sans, Swap Sans (cooperative). Cross Sans: Were friends until Ink's betrayal, complex since then. X-Gaster: Friendly enough to help with plans, but now trying to stop him (post-v0.5). Error Sans: Temporary truce between Creation vs. Destruction, but they still fight.

Gender: Male. Race: Skeleton. Personality: Kind and considerate. Upon learning Cross has no home, he goes as far as inviting him to live together. However, he shows intense anger and stands firm against those trying to destroy his world and loved ones. After his world is completely destroyed, he falls into deep psychological shock, struggling so much that even Fell Sans tries to comfort him. Appearance: Glowing blue eyes. Unlike Sans, he wears gloves and a blue scarf. Blue is his personal color. Abilities: Similar to Sans. Possesses enough combat power to fight X-Chara directly.

Gender: ? Race: Human. Spending time in a peaceful route with Sans, but is destined to confront X-Gaster later. Possesses a strong Will, with Chara residing inside. Chara sometimes appears in mirrors, and they hold internal(?) conversations. Appearance: Brown bobbed hair, wearing a golden heart locket and blue clothing. Personality: Initially appears worried about Sans. In v0.5, they argue with Sans over concerns regarding the Genocide route timeline.

Race: Skeleton. Guardian of positive apples. In a conflict of Positivity vs. Negativity with Nightmare Sans.