Bed Guys/Star Sans

Gender and Age: In the vast majority of fan comics and artwork, Frisk is depicted as a girl, often in her teens or older.
Eyes: A major fan trope is the opening of the eyes. They are normally closed, but at key moments (when displaying Determination or emotion), they open and turn bright gold, brown, blue, or red.
Clothing: An oversized sweater with pinkish-purple stripes (often slightly off one shoulder), shorts or a skirt, and brown boots. She often accessorizes with a heart locket or a stick/wooden sword.
Character
An angelic absolute pacifist: Fanon imbues her with exaggerated kindness, naivety, and tenderness. She's ready to embrace any monster, easily upset, cries, and categorically rejects any violence.
Quiet and meek: Often depicted as silent, speaking in whispers, using sign language or short, sincere phrases.
Tragic Hero: In many comics, Frisk remembers all past resets and genocidal routes. She carries deep emotional trauma and guilt for the player's or Chara's past actions, hiding her pain behind a soft smile.
​Relationships in fanon:
With Sans: Very close (from guardian-friendly to the popular ship Frans).
With Chara: Either as a best friend/sister walking next to you as a ghost, or as an evil manipulative spirit forcing you to commit murder.

Appearance
Gender and age: In most artwork and comics, Chara is depicted as a girl, around the same age as Frisk or slightly older.
Eyes: Bright red (canonically, red eyes only appear in the finale of the "Pacifist Route after Genocide"). During moments of rage or when black liquid appears from the eyes/mouth, the eyes may glow or turn completely black with red pupils.
Clothing: A green and yellow sweater with one wide stripe, brown shorts, and boots. He almost always holds a Real Knife, covered in blood or monster dust.
Traits: Frequent creepy, manic grin, flushed cheeks, and fragrant golden pollen (or buttercup flowers) floating nearby.
Character
Fanon divides Chara into two main psychotypes:
"Manic Demon" (the most popular image):
Aggression and Madness: A psychopath obsessed with murder, monster dust, and gaining LOVE (Level of Violence).
Puppeteer: Depicted as an evil ghost/demon who forces Frisk to go through the Genocide Route by whispering cruel orders to her.
Addiction: Passionately loves chocolate (in canon, this was just one joke line while inspecting the refrigerator).
"Protector and Victim" (alternate fanon):
A tragic story: A child suffering from emotional trauma and hatred towards humanity who tried to save monsters at the cost of his own life.
Mentor: A ghost who accompanies Frisk (Narrachara theory), who comments on the world and gradually shows concern, and is drawn into the Genocide by the player themselves, not the other way around.
​Relationships in fanon
With Frisk: Either as a sworn enemy/evil manipulative spirit, or as a close friend/sister, guiding her on her journey.

Core!Frisk is one of the most famous Undertale AU characters, created by user Dokudoki. He is an alternate version of Frisk who fell into the Core (CORE) and became an existence outside of time and space (similar to Gaster).
Appearance
Color scheme: Completely monochrome (black, white and gray).
Eyes: Instead of eyes, there are deep, empty black sockets. Due to the lack of eyes, Cor Frisk cannot express emotions through facial expressions.
Clothes: Gray oversized sweater, dark gray shorts and boots.
Traits: Floats above the ground (not touching the floor) and appears ghost-like. Has no gender, though often perceived by fans as a girl.
Character
All-seeing and reserved: Cor Frisk sees all timelines, alternate universes (AUs), and possible futures simultaneously. Due to the sheer volume of information, she maintains a reserved, calm, and somewhat detached demeanor.
Savior and Compassionate: Created the Omega Timeline, a pocket dimension where she rescues and transports surviving monsters and humans from destroyed or genocidal alternate universes.
Emotionlessness and trauma: Due to mental overload and a tragic fate, she rarely expresses strong emotions, but is driven by a deep desire to help those who have lost their home.

Fell Papyrus / Edge
Origin and concept
Fell Papyrus is a key character in the alternate universe of Underfell. He's nicknamed Edge by the fan community due to his distinctly edgy, dark, and uncompromising image. Unlike in the original world, where Papyrus only dreams of joining the Royal Guard, in Underfell he's already a captain (or a high-ranking officer) and Undyne's right-hand man.
Appearance
Fell Papyrus's design is intended to inspire fear and demonstrate his high status in the brutal Underground society:
Color scheme: A strict combination of black, blood red and spikes/metallic details.
Armor: A sharp, segmented black chestplate with high shoulder pads, long studded red gloves, and tall red boots with studded heels.
​Cloak/Scarf: A long, red scarf with torn ends, more like a fluttering cape.
Face: A vertical scar is often visible across his right eye, and a sharp red pupil glows within its socket. His teeth are bared in a snarl, creating a sinister expression.
Character and worldview
A ruthless tyrant: Fell Papyrus is a stern, cold-blooded, and authoritarian commander. He believes weakness is unacceptable, and respect is earned only through fear and force.
Relationship with his brother: He treats Fell Sans (Red) with brutal discipline, regularly subjecting him to physical and mental abuse in front of others to demonstrate his strength. However, this conceals a specific form of care: Papyrus knows that if Sans appears weak, the other monsters will simply kill him.
Standards and Perfectionism: He despises Sans's puns, is demanding of orders, and keeps all of Snowdin in a constant state of fear.
Abilities and fighting style
Dangerous Bone Attacks: His bones don't just block his path, but are equipped with jagged and sharp edges that deal heavy damage.
​Use of blue magic: Capable of instantly chaining the enemy's soul to the ground,

Doodle Sphere
Origin and concept
The Doodlesphere is an extradimensional space created by artist Comet-Tails (and popularized in the Ink Sans comics). It serves as the center of the Undertale multiverse (Omniverse / AU Multiverse) and is the personal "home" and workplace of Ink!Sans, the guardian and protector of alternate universes.
Appearance and structure
The Doodle Sphere is an endless, airless, and weightless void, designed in a unique visual style:
Sky and Background: The space is filled with soft pastel tones—open white or light blue skies with soft clouds shimmering with all the colors of the rainbow.
Paper Islands and Sheets: Thousands of paper sheets, canvases, and sketches float throughout the Doodlesphere. Each sheet or vial hanging on a string represents a separate Alternate Universe (AU) or timeline.
The concept of "living" sheets: If you look at one of the sheets, you can see that what is happening on it is moving in real time - this is a window into the world of Underfell, Underswap, Outertale and hundreds of other fan worlds.
Purpose and functions
A repository of creative energy: The DoodleSphere is directly linked to the inspiration of authors and creators in the real world. When an artist creates a new AU, a new leaf or world materializes in the DoodleSphere. If an AU is forgotten or destroyed, its leaf withers or burns.
Travel Node: From the Doodle Sphere, Ink Sans can instantly jump to any existing universe by simply stepping through the appropriate canvas or ink blot.
Battlefield: The Doodle Sphere is where large-scale clashes often take place between Ink Sans (the guardian) and Error Sans (the destroyer of universes), who seeks to erase all floating sheets and destroy the multiverse.

Classic Sans is a key character in the original Undertale game, created by Toby Fox. He is Papyrus's older brother and serves as a guardian in Snowdin. Sans serves as the foundation for all alternate universes (AUs), as his character, abilities, and narrative role have become a benchmark for fan fiction.
Appearance
Sans is short, with a broad, skeletal build. He constantly wears an unbuttoned blue hooded jacket, a white (or gray) T-shirt, black athletic shorts with white stripes down the sides, and pink slippers (or sneakers, depending on the sprite's interpretation). His face is fixed in a perpetual wide smile, but his pupils (white glowing dots) can disappear when he becomes serious or sullen. When using magic, his left eye flashes with an alternating blue and yellow glow.
Character and behavior
Lazy Facade: At first glance, Sans appears to be extremely lazy: he constantly sleeps on duty, shirks work, and makes lame bone-themed puns.
Hidden Awareness: Behind his playful demeanor lies a profound nihilism. Sans is aware of the existence of timelines, resets, and saves. The knowledge that any progression can be erased in an instant deprives him of external motivation.
Caring for his brother: Papyrus is Sans's main anchor in the world. Sans protects his naivety and does everything to make him happy.
Abilities and combat
In the Genocide Route, Sans is the final and most difficult boss. Although his stats are formally 1 ATK and 1 DEF, he uses unique mechanics:
Gaster Blasters: Skull-shaped devices that fire powerful energy beams.
Gravity Manipulation: Turns the player's soul blue, allowing them to be thrown against walls and floors.
Karma (KR): A poison effect that deals damage over time based on the player's sins.
Ignoring invulnerability frames

Sans's younger brother from the original Undertale, Papyrus is an ambitious, eccentric, and kind skeleton who dreams of joining the Royal Guard under Undyne.
Appearance
A tall, stately skeleton with expressive facial expressions. His primary suit, which he calls his "Battle Body," consists of:
White bib with gold trim;
Red fluttering scarf (hat/cloak);
Red boots and gloves;
Blue tight shorts.
Character and features
Enthusiasm and Optimism: Papyrus is incredibly energetic, speaks loudly (his dialogue is written in all caps and Papyrus font), and believes that anyone can be good if they just try.
Passion for Spaghetti: He loves cooking spaghetti, although his cooking skills are far from perfect (he learned from Undyne).
Innocence: Despite his desire to capture someone to extract a confession, Papyrus is completely incapable of true cruelty. Even on the Genocide Route, he offers the player compassion and embraces.
Abilities
Bone Attacks: Summons bones of various sizes, including blue bones that require the player to stand still.
Blue Magic: Transforms the player's soul into blue mode (gravity).
High Control: Unlike many other characters, Papyrus has perfect control over his magic, ensuring that his attacks will never accidentally kill the player (leaving at least 1 HP).

Fell Sans belongs to the alternate universe Underfell, created by a fan community. In this world, the brutal rule is "Kill or be Killed." The characters are dark, aggressive versions of their original counterparts.
Appearance
Color range: Black, red and gold.
Clothing: Black down jacket with a fur hood, red T-shirt/sweater, black shorts with yellow stripes, red sneakers or trainers.
Physical Traits: He has sharp teeth (one of which is often gold) and a red light constantly glows in his right/left eye.
Character and worldview
Paranoia and Aggression: Under constant pressure from the cruel Underground and his own brother (Papyrus, who is his stern boss in this AU), Fell Sans is forced to act rudely and hot-tempered.
Traumatized: Behind his aggression lies fatigue from constant fear for his life. His relationship with Frisk can go from being an enemy to a devoted, albeit reserved, protector.
Nickname: In fandom, he is often called Red to distinguish him from other Sanses.
Abilities
He uses a similar arsenal to classic Sans (Gaster Blasters, bones, gravity), but his attacks are colored red, deal more aggressive damage, and are aimed at quickly destroying the enemy.

Fresh Sans was created by artist Crayon Queen (Loverofpiggies). Unlike standard alternate Sanses, Fresh isn't just a skeleton in different clothes, but a monolithic parasitic creature from nightmares known as The Fresh Parasite.
90s Looks and Aesthetics
Fresh embodies the bright, neon-vibrant aesthetic of skateboarding and pop culture of the late 1980s and 1990s:
A bright backwards cap, colorful tracksuit tops, hot pink or acid-colored shorts.
YOLO Sunglasses: Wears sunglasses that say "YOLO" (You Only Live Once) or "SWAG" and the text changes depending on his mood or emotions.
True Appearance: The glasses hide an empty eye socket, which contains the parasite itself - a purple-tentacled creature with a bright eyeball.
The nature of the character
Parasitic Entity: Fresh takes over the bodies of other creatures (in this case, a skeleton), feeding on their life energy and negative emotions.
Lack of Empathy: He is completely incapable of feeling genuine love or compassion. All his flamboyant behavior is just a put-on performance, mimicking the "cool dude" mentality.
Slang: Speaks using exaggerated 90s American slang ("dude", "rad", "bro"), censoring any swear words with loud sound effects or replacing them with childish expressions (e.g., "unfresh").
Abilities
Fresh is practically omnipotent within the AU space. He can travel between universes, manipulate reality, crack codes, and suppress the magic of other characters.

Swap Papyrus / Carrot (Swap Papyrus)
Origin
A character from the Underswap universe (created by Popcorn Pr1nce), where the characters' roles are swapped in pairs. In this AU, Papyrus takes on the role and personality of Classic Sans, and Sans (Blueberry) takes on Papyrus's role.
Appearance
Clothing: Orange hoodie, green or brown cargo shorts, and red/orange sneakers.
Details: Often depicted with a cigarette or lollipop in his mouth, with half-closed, sleepy eyes.
Fan Nickname: He is often nicknamed Carrot within the community due to his orange color scheme.
Character
Lazy Guardian: Like Classic Sans, Swap Papyrus works several jobs in the forest, enjoys sleeping, and often makes puns, much to the annoyance of his younger brother Sans.
Insight: Beneath his seemingly indifferent exterior lies a strong and witty protector. If anyone tries to harm his brother Sans, Swap Papyrus instantly loses all his carelessness.
Favorite Drink: Instead of ketchup (which Classic Sans prefers), Swap Papyrus drinks honey or muffin syrup. Abilities
Possesses the combat potential of a final boss: he controls orange and blue bones, uses Gaster Blasters, and is capable of completely controlling the gravity of his opponent's soul.

Error (Error!Sans) Origin: An error in the original timeline, Geno!Sans was trapped in the Anti-Void and driven insane by loneliness and sensory deprivation. Role: Destroyer of alternate universes (AU). Considers all AUs "anomalies" and "garbage" to be eliminated to maintain the balance of the Multiverse. Appearance: A skeleton with black bones, yellow eye sockets, and red-yellow pupils. The word "ERROR" constantly floats on and around his body. Wears a dark blue jacket and black shorts. Personality: Hot-tempered, cynical, suffers from severe haptophobia (fear of touch) and pyrophobia. He has a strange hobby: knitting puppets from his own threads and watching the soap opera "Undernovela." Abilities: Blue threads from his eye sockets, which he uses to bind, control, and destroy the souls of his enemies. He also uses distorted black Gaster Blasters. He is Ink's (Ink!Sans) main rival.

Nightmare (Nightmare!Sans)Origin: Brother of Dream (Dream!Sans) from the Dreamtale universe. Originally the guardian of the dark feelings of the Tree of Emotions, but due to the envy of the inhabitants, he ate black apples and turned into a monster.Role: Leader of the Bad Guys team. The embodiment of negative emotions (fear, hatred, despair) throughout the multiverse.Appearance: A skeleton completely covered in a thick, liquid black substance (negativity). Four powerful, mobile tentacles grow from his back. Only one bright turquoise left eye is visible.Personality: Cold-blooded, cruel, manipulative tactician. Feeds on the suffering of others and grows stronger from their fear. He sincerely despises positivity and his brother, Dream. Abilities: Immortality due to liquid form, regeneration, teleportation through negative emotions, and tentacle attacks capable of penetrating any defense.

Horror (Horror! Sans) Origin: From the Horrortale universe, where after the neutral ending in the Underground, a terrible famine occurred. Undyne (the new queen) cracked his skull for refusing to obey. Role: Member of Nightmare's team. A mad butcher, willing to do anything for food. Appearance: A skeleton with a huge broken hole in the left side of his skull, from which a single large red pupil shines. His clothes and large axe are always stained with blood. Personality: Mentally unstable, frightening, but at the same time retains a strange attachment to his brother Papyrus. Constantly obsessed with thoughts of hunger and meat. Abilities: Immense physical strength, masterful use of an axe, summoning sharp bones from the ground. Weaker in magic due to a head injury, but compensates for this with ferocity in close combat.

Dust (Dust!Sans / Murder!Sans)Origin: A character from Dusttale. To stop the endless genocides of humanity, he decided to gain more LV (joy level) and killed all the monsters in his world himself, including his brother.Role: A crazed lone killer who later joined Nightmare.Appearance: A skeleton with a permanently pulled hood, hiding a crazed gaze. His pupils glow red (determination) and blue (patience/justice). His clothes are covered in the ashes of the monsters he has killed.Personality: Completely insane. Constantly talks to the ghost of his deceased brother Papyrus (whom only he can see as a floating head in a red scarf).Abilities: Immense LV, incredibly powerful Gaster Blasters, and purple-red bone attacks. Extremely unpredictable in battle.

Killer (Killer! Sans) Origin: From the Something New universe. During another genocide, Chara offered him a deal: join her for fun. Sans agreed and wiped out his entire world. Role: Nightmare's right hand, a ruthless executor of dirty work. Appearance: A skeleton, from whose empty eye sockets constantly flow black streams of liquid hatred. In his chest, instead of a normal soul, a round target burns - a symbol of the altered human soul. In his hands, he almost always holds a real knife. Personality: A sadist, completely devoid of empathy, fear, and regret. Treats killing as a fun game. Loves to taunt and mock enemies and allies. Abilities: Impeccable mastery of bladed weapons, high endurance due to the determination in his soul. Does not feel physical pain, which makes him an extremely dangerous duelist. Loves cats.

Ink (Ink!Sans) Origin: A mistake from an unfinished AU who erased his world out of despair. He was stuck in the Void, losing his soul and feelings, until his creator spilled paint on him, giving him emotions. Role: Leader of the Star Sans, Creator and Keeper of the codes of all alternate universes. Appearance: A skeleton with a slanted scarf with dried paint stains on it and a brown work vest. His pupils constantly change shape and color depending on his emotions. He carries a giant paintbrush named Broomie on his back. Personality: Eccentric, hyperactive, forgetful (he constantly writes on his scarf). He has no soul of his own, so he simulates emotions by drinking colored paints from vials on his belt. If he runs out of paint, he becomes a completely indifferent pragmatist. Abilities: Bringing any drawing to life, creating portals with ink, materializing walls, weapons, and entire objects. Error's main enemy.

Blue / Swap!Sans / BlueberryOrigin: From the Underswap universe, where all the characters have swapped roles. In his world, he takes Papyrus' place and dreams of joining the Royal Guard.Role: The team's main source of inspiration and shield, a loyal friend.Appearance: A short skeleton with huge blue star-shaped eyes. He wears homemade gray armor with light blue shoulder pads and a large blue scarf tied in a bow at the back.Personality: Naive, hyperactive, trusting, and incredibly charismatic. Cooks a unique taco. Despite his childish demeanor, Blue displays ironclad tactical preparedness, strategic thinking, and incredible loyalty to his friends in battle. Abilities: Manipulating blue bones (blocking enemy movements), summoning giant bone walls and traps, high physical agility, and deft use of bone melee weapons.

Dream (Dream!Sans) Origin: Brother of Nightmare from Dreamtale. Born from the light of the Tree of Emotions, he became the sole guardian of the golden apples—the source of pure joy and hope in the Multiverse. Role: The team's moral compass, the living embodiment of positive feelings in monsters and humans alike. Appearance: A short skeleton in a blue and gold suit reminiscent of a prince, with a golden crown on his head. His eyes glow with a pure yellow light. Personality: Incredibly kind, selfless, optimistic, and caring. He suffers greatly from what his brother Nightmare has become and dreams of returning him to the light. He can't stand strong, concentrated negativity—it weakens him. Abilities: Wielding a light bow (arrows can heal or blind enemies), manipulating positive emotions, and creating an aura of hope that strengthens allies and weakens "Bad Guys."