underverse!!

A huge knife and control through piercing. His main weapon is capable of not only inflicting damage but also temporarily subduing a victim if Cross stabs them. This is risky: the longer he maintains control, the more X!Chara exerts its influence on his consciousness.
Code Hack. In conjunction with X!Chara, it can "rewrite" small fragments of reality: change locations, erase individual memories, and disable enemy abilities. It works like a system command: it "selects a target" and applies a patch.
Overwrite. Extreme measure: X!Chara can activate a complete overwrite of a small area of ​​space, erasing everything that was there and replacing it with a new state. This is extremely dangerous and can harm Cross himself.
Teleportation and dashes. He moves in short, sharp bursts, often combining teleportation with attacks. This confuses the enemy and gives them no time to react.
Manipulation of gravity and souls. Can briefly alter gravity in the battlefield and affect the enemy's soul, causing them to feel guilt or fear—this is also part of the X!Char's influence.
Instability of reality. Due to the coexistence of two personalities, his mere presence slightly "shakes" the timeline: in places where he remains for long periods, minor glitches may occur—for example, objects briefly disappearing or changing color.
What does he like?
Chocolate and tacos. Among fans, these have become ingrained as his little joys, helping him forget, if only for a moment, the weight of his power.
Moments of silence. He values ​​short periods when no one demands anything of him and he can simply sit, not worrying about X!Chara trying to escape again.
Loyalty and honesty. He values ​​people who speak frankly and keep their word: that's rare in a world where everyone is taking advantage of everyone else.
A connection with those who remember his past. Those who know his history and don't judge him solely by his current actions are very important to him.
Control over the situation. He feels calmer when he understands what is happening and can anticipate threats in advance.

View
Cross's look combines "black and white austerity" with aggressive details that highlight his connection to the code and to X!Chara.

Skeletal structure. Looks like Sans, but with sharper, more pointed features. His posture is often tense, as if he's ready to spring into battle at any moment.
Eyes. The left eye glows a soft blue (his own magic), the right one a bright red (X!Chara's influence). When X!Chara takes over, both eyes can turn red, and a "glitch" effect appears around them—as if the image is slightly distorted.
Clothing. Black T-shirt, white unbuttoned short-sleeved jacket, long scarf secured with white straps. Shorts and boots with the letter "X" on them, and a belt with the same marking.
Accessories: Around his neck is a yellow heart-shaped medallion (an important symbol of his connection to his past and to Frisk from X-Tale). He is often depicted holding a huge knife—his signature weapon.
Effects. Digital "cracks" and brief flashes, similar to screen errors, may flicker around him. When activating his abilities, the surrounding space "shifts" slightly, as if the world's code were temporarily broken.
Details. Sometimes thin red lines are visible on the bones—this is a visualization of the influence of the X!Char, which literally "grows" through his magic.
Capabilities
Cross's powers are a blend of Sans's magic and X!Chara's hacking abilities: he breaks the rules of reality, but at the cost of his inner balance.

X-Blasters. His blasters are different from the classic ones: they have four "eyes" with red pupils, and the beams are X-shaped. They strike not only the body but also the timeline structure, creating ruptures.
Dice with a dual effect. He can create dice that act as traps or barriers, as well as energy conduits. In X!Enchantment mode, the dice turn red and black and can "infect" opponents with digital poison.

Character
Cross is Sans, who lives in constant conflict between himself and the other person inside him: X!Chara is trapped within his body, making him simultaneously strong and vulnerable. He's not so much "evil" as he is cornered by circumstances and forced to make tough decisions.

Key features:

Internal conflict. He constantly balances between his own desire to protect his loved ones and the destructive power of X!Charity. Sometimes Cross acts decisively, and the next moment he freezes, fearing that his other personality will take control.
Tired of the endless battles. He's tired of being a tool in other people's plans (HGaster, Nightmare, and others). He longs for peace, but the world doesn't give him a chance to stop.
Hidden Kindness. Despite his dark image and brutal methods, he genuinely cares for those he considers family or friends. His care often manifests itself in attempts to "get them out of the line of fire."
Guilt. He takes the consequences of his actions very hard, especially if someone was hurt because of his power or because he failed to restrain X!Chara in time.
A cautious trust. It doesn't reveal itself immediately: it's been used too often. But if someone has proven their reliability, Cross will stand by them to the end.
Impulsiveness in critical situations. When the threat is real, he acts quickly and harshly, without wasting time on lengthy explanations.
What doesn't he like?
When he's used as a weapon, he hates it when others see him only as a force and a tool to achieve their goals.
A reminder of the lost universe. Any mention of X-Tale and what he lost causes him acute pain and irritation.
Royal armor/guard armor. In some versions of the lore, he feels an almost physical aversion to them—he associates them with coercion and control.
Cows. This is a lingering meme element: for some reason, he can't stand cows and tries to stay away from them.
Senseless cruelty. He is ready to be tough if it is necessary for protection, but does not condone violence

Blue Soul Control. In this special form, he can move any object (living or dead) up to 500 meters with his mind. He can also completely destroy a soul if he deems it "incorrect."
Divine Beam. Fires a blast of pure energy from her fingers that destroys any "non-standard" code: this is especially dangerous for beings with altered souls, hybrids, and those who violate the basic laws of the multiverse.
Dark Blasters. His blasters are more powerful than regular ones: they fire concentrated blasts of "anti-code" that not only deal damage but also erase the target from the timeline.
Manipulation of minds and souls. Can take control of others' souls, distort perception, and make the victim see "errors" where none exist. Often uses this to make enemies doubt their own reality.
Pixelation of Space. Transforms air and objects into tiny pixels, forming barriers, traps, or even weapons. Can also use this for teleportation: disintegrate into pixels and reassemble in another location.
"Puppet Master" form (shared with Error). In dire need, he can merge with Error Sans into a single form, gaining access to his threads and his own power. In this state, his speed exceeds the speed of light, and his regeneration almost completely negates death. Lockout mechanics. He can "disable" the abilities of other Sanses (SAVE/LOAD, teleportation, gravity manipulation), treating them as "unnecessary functions" and removing them from the current timeline. What he likes
Order and symmetry. He likes everything to be logically arranged, without unnecessary emotion or chaos.
Knowledge and Archives. He collects and organizes information about universes, considering it his duty.
When his plan works perfectly, for him, the "clean" execution of a task is the highest reward.
Train and guide. In his relationship with Error, he displays a rare level of care: it's important to him that his student doesn't break under the weight of his power.
Silence and solitude. In silence, he better hears the "pulse" of the multiverse.

A reminder of his own mistakes. There are things he'd rather erase from his memory forever, and any hint of them sends him into a fit of cold rage.
Error 404's image is built on "digital decay": he looks like Sans, but as if he's constantly being "redone" and "erased." The dice. Not pure white, but with blue and black digital stripes, as if lines of code were running across them. Where there's a "glitch," the dice can flicker, disappear, and reappear.
Eyes. Both eyes glow bright blue, but around them are black lines, reminiscent of screen cracks or video compression artifacts. Sometimes, what "flows" from the eyes aren't tears, but lines of text (codes, system messages, fragments of universe names).
Clothing. A long white jacket with blue circles and lines reminiscent of diagrams. On the back is a large number "404." Under the jacket is a black sweater, pants with blue lines, and simple blue slippers with crosses.
Hands. The fingers have blue tips, and the hands themselves are black due to lag, as if part of the texture didn't load.
Effects. Around him, there's a slight ripple, like on an old monitor, and pixelated particles that sometimes disintegrate, sometimes reassemble into new patterns. During strong surges of power, the space around him "mosaics"—breaks into squares and distorts.
Posture and expression. Most often, he stands upright, almost statuesque, as if he's economizing on movement. His smile is rare and unnerving: it's not joy, but satisfaction from a "perfectly executed job."
Capabilities
Error 404 manipulates the very fabric of the multiverse like a code: it doesn't just break, it rewrites.

Manipulation of code and reality. He can "edit" fragments of universes: delete objects, change the rules of physics, erase memories, and even rewrite character traits. It works like a system command: he "selects" a target and applies a patch or deletes it.

Character
Error 404 isn't just a "mistake," but a being that has taken chaos and destruction under strict control. It thinks like a disaster architect: for it, the universe is code, and any universe containing "incorrect" emotions or "broken" fate lines is a bug that must be fixed (usually by deletion).

Key features:

Cold calculation. He doesn't get angry without reason: every destruction, every timeline disruption is a decision made after careful analysis. His rage is always rational.
The "supreme judge" complex. He sincerely believes he knows what the "correct" order should look like and is willing to rewrite reality to achieve it.
A thirst for knowledge as a weapon. He collects data about universes, souls, and codes and uses them as tools. For him, information is power, and ignorance is weakness.
A reserved affection for Error. In some versions of the lore, he acts as a "mentor" or "older version" of Error Sans: he's strict, sometimes cruel, but deep down, he wants Error to become stronger and not break.
Hidden pain and loneliness. Behind the façade of the all-powerful "error manager" lies someone who has seen too much and lost too much. He rarely shows vulnerability, but it's there.
Intolerance for chaos without purpose. If someone breaks code simply for fun (like Fresh) or out of blind rage (like early versions of Error), they react especially harshly: for them, senseless destruction is an even bigger bug.
What doesn't he like?
Chaos without purpose. He perceives senseless destruction, emotional outbursts, and "stupid" mistakes as a threat to the stability of the multiverse.
Lies and distortions of facts. For him, truth is the foundation of the code, and any distortion of reality without his sanction is a crime.
A weakness that no one tries to overcome. He can't stand it when someone gives up simply because they're scared or struggling.
Violation of his rules. If someone tries to bypass his controls or hack his systems, he reacts with the utmost severity.
A reminder of one's own mistakes.

Gaster Blasters. His blasters are larger and brighter than classic Sans's, with a golden or pinkish glow. They not only deal physical damage but also "knock" the opponent's resolve out, temporarily weakening their will to fight.
Time Control (limited). Through determination, he can slow down time around him for short periods to dodge or deliver a precise blow. However, this greatly drains him and can cause bursts of decay.
Preservation and protection. He can create temporary "islands" of stability where decay is suspended. This allows him to protect allies or preserve important objects, but requires a huge expenditure of energy.
Reading intentions and resolve. Geno can sense the level of resolve in others and understand how committed an opponent is to the end. This helps him anticipate their tactics.
Self-healing (with reservations). He can temporarily "glue" his disintegration together, but this doesn't heal it; it merely postpones the inevitable. The more often he does this, the more unstable he becomes.
What does he like?
Stability and peace. He truly cherishes moments when nothing explodes, no one fights, and when he can just sit and breathe.
Those who don't give up. He respects tenacity and resilience, even if it's in the smallest things. For him, it's a sign that hope still lives.
Simple rituals. A cup of tea, a casual conversation, stargazing—these things help him feel a little more whole.
Protect and support. It's important for him to know that his efforts are helping someone, even if he doesn't say it out loud.
Frisk (in the Aftertale lore). In this universe, they share a common history of survival and fighting decay, and he sincerely values ​​this connection.

View
Geno Sans's most distinctive visual feature is his leaky right eye, which symbolizes the decay and instability of his existence.

The right eye. It's the one that's "leaking": it seems to be leaking a luminous substance (most often depicted as a golden-white or pinkish liquid, resembling molten light). Sometimes the eye appears as a crack, oozing energy rather than the usual liquid. This isn't just a wound, but a sign that his body is giving in to his resolve.
Left eye. Usually remains normal, but may glow when Geno uses his powers. Sometimes the pupil turns bright blue or white.
Bones. Thin red or golden cracks appear on them, as if the bones are slowly crumbling. These cracks can shimmer when determination is particularly strong within.
Clothing. He's most often depicted wearing a white hooded jacket (as opposed to the classic black one). The jacket is noticeably worn: it has scuffs, stains, and sometimes marks from burns or energy surges. Underneath the jacket, he wears a simple T-shirt, shorts, and simple, unpretentious shoes—he's not into style.
Posture and expression. He often stands slightly hunched, as if conserving his energy. His smile is rare, usually soft and slightly sad. In moments of tension, he straightens up, and a hardness appears in his expression.
Effects. Sometimes, slight ripples or "sandy" particles are visible around it—a visualization of how it's gradually crumbling. At intense moments, light can escape from cracks in the bones.
Capabilities
Geno's powers are built on determination, but they come at a cost and require constant monitoring.

Determination as a weapon and a curse. He can enhance his attacks with determination, making bones and blasters more powerful, but each use of the power accelerates his decay.
Bone manipulation. His bones aren't just sharp—they can be unstable, change shape, and create areas of increased pressure. Sometimes they literally "explode" with energy upon impact.

Character
Geno Sans is a Sans who survived the genocide and survived only through determination, but this force is literally eating away at him from the inside. He balances between his desire to protect what remains of the world and the knowledge that he himself is slowly crumbling.

Key features:

Fatigue mixed with tenacity. He's incredibly exhausted: every day is a struggle not only with his enemies, but also with his own disintegration. Yet he stubbornly holds on, believing he must be a support for those who remain.
Discreet caring. He doesn't shower others with compliments or create drama, but he does everything he can to keep others safe. He often takes on the toughest work and tries not to show how hard it is.
Guilt. Geno is deeply saddened by his failure to save everyone. For him, every loss is a personal failure, even if objectively he did everything possible.
A cautious hope. Despite the gloomy situation, he doesn't want to completely lose faith in the best. But he hides this hope deep inside, afraid it will prove false.
Patience for the weaknesses of others. He understands that both humans and monsters break under pressure, and he tries not to judge too harshly. Being on the edge himself, he is especially sensitive to the pain of others.
An internal struggle with determination. The determination that sustains him simultaneously destroys his body and mind. He must constantly control it to avoid losing himself completely.
What doesn't he like?
Senseless cruelty. He's seen enough pain and doesn't want suffering to become normal or entertaining.
When he's considered "immortal" because of his determination, he knows the value of this power and hates it when others underestimate how destructive it is.
Ignoring other people's feelings. He finds it unbearable when someone suffers while others pretend nothing is happening.
His own disintegration. He tries not to show weakness, but the thought of himself gradually disappearing weighs heavily on him.
False hopes. If someone clings to illusions and refuses to see reality

Knowledge of game mechanics. He understands how SAVE, LOAD, and RESET work, and can react to timeline resets. This makes him a particularly dangerous opponent in Genocide.
Conservation of resources. His strength is built on spending minimal mana and dealing maximum damage with short but precise strikes.
Intention Reading. Able to sense the opponent's intentions and emotions, anticipating their actions before they take them.
What does he like?
Relaxing and doing nothing. For him, "just sitting and not straining yourself" is almost the highest value.
Make jokes. Especially puns and knock-knock jokes: even if no one else laughs, it makes you feel better.
Mustard and ketchup. He likes to add them to almost everything and sometimes jokes about it.
Time with Papyrus. Despite the constant teasing, he sincerely cherishes the time spent with his brother: sharing meals, talking, even just sitting next to him.
Little joys. A cup of hot chocolate, a quiet evening, a good joke—he appreciates the simple things.

View
The classic Sans look is relaxed, casual, and no-frills.

Skeletal structure. A short skeleton with a wide, slightly lazy smile and a relaxed posture.
Eyes. White pupils that can disappear when he's serious or using magic. During battle, his left eye sometimes glows blue—a sign that his abilities are activating.
Clothing. Black jacket (often with a fur collar), red T-shirt, black shorts with a white stripe, light blue slippers. This outfit has become iconic and easily recognizable.
Details. Rings are often visible on his fingers, which he magically holds in place to prevent loss. He is sometimes depicted holding a cup of hot chocolate or a bottle of ketchup or mustard, highlighting his everyday habits.
Posture and expression. Almost always relaxed, as if about to fall asleep. His smile is friendly, but there's a hint of cunning in it.
Effects: In battle, a faint blue aura appears around him, and his dice and blasters have a distinctive blue glow.
Capabilities
Sans appears lazy, but that's precisely why he's so dangerous: he uses his power sparingly and precisely.

Bone Manipulation. Can create and control multiple bones, directing them with precision. Bones appear where the enemy least expects them and move along complex trajectories.
Gaster Blasters. Uses skull-shaped blasters that fire energy beams. They are fast, powerful, and can change trajectory.
Teleportation and evasion. Capable of instantaneous movement and evasion, often doing so with such ease that it seems he simply "stepped" into another location.
Gravity Control. Can alter the direction of gravity in a limited area, confusing and disorienting the enemy.
Knowledge of game mechanics. He understands how SAVE, LOAD, and RESET work, and can react to timeline resets. This makes him a particularly dangerous opponent in Genocide.

Character
Classic Sans is a lazy, sarcastic, yet surprisingly insightful and caring skeleton. He appears carefree and relaxed, but in reality, he notices a lot and takes on far more responsibility than he lets on.

Key features:

Laziness as a way of life. He sincerely tries to do as little as possible and often jokes about "not wasting mana" and "not straining himself." But if the situation is serious, he instantly becomes focused.
Sarcasm and silly jokes. He loves puns and knock-knock jokes, even if they're not funny at all. He uses them as a way to lighten the mood and show that he doesn't take things too seriously.
Insight and intuition. Sans is an excellent reader: he understands almost immediately who's in front of him and what their intentions are. In genocide, he sees right through everything and doesn't try to play the "good guy."
Hidden caring. He tries not to be intrusive, but always watches over those he cares about: Papyrus, Frisk, the people of Snowdin. His care isn't expressed in grandiose words, but in small gestures and a willingness to intervene when needed.
Fatigue and the weight of knowledge. He knows a lot about timelines, SAVE/LOAD, the nature of the world—and it weighs heavily on him. Hence his "laziness": sometimes it's easier to do nothing than to face the consequences of your actions.
A sense of justice. He doesn't strive to be a hero, but he clearly understands where the line is that shouldn't be crossed. And if someone crosses it, Sans is ready to act harshly.
What doesn't he like?
Unnecessary stress. If he doesn't have to do something, he won't. But if he has no choice, he'll do it as efficiently as possible.
Cruelty for the sake of cruelty. He is calm about conflict, but disapproves of violence that serves no purpose.
When loved ones suffer, any threat to Papyrus or his other friends instantly jolts him out of his "lazy" state and makes him dangerous.
Being misunderstood. He doesn't like being perceived as just a "funny skeleton," ignoring his serious side.
Too many responsibilities

Time Rewind (for short periods). Can rewind time by 20–30 seconds to correct a mistake or avoid damage. This ability can be used for up to a minute at a time, after which it requires a long cooldown.
Green Smoke. Dispels smoke that obscures vision and disorients enemies.
Strengthened by "coolness." The more attention and chaos around, the stronger it becomes: the crowd, the music, the flashing lights fuel it.
Tendrils and parasitic attacks. Tendrils can sprout from any part of the body—they are incredibly strong and used for grasping, holding, or attacking.
Healing Block: His attacks can temporarily disable an enemy's regeneration and healing abilities.
Dance combos. In battle, he moves to the rhythm of the music, and his attacks are synchronized to the beat: the more precise the rhythm, the greater the damage and speed.
What does he like?
To be the center of attention. It's vital for him to be looked at, admired, and discussed.
Music and dancing. Especially themes like Duck Tales and Captain Planet—those are his favorite "soundtracks."
Skateboarding and speed. She loves the feeling of movement and freedom, even if it's just a way to escape her problems.
Neon colors and 90s style. His entire aesthetic is built on this: he sincerely believes that "style is power."
Chaos and fun. For him, "fun" means loud effects, explosions, screams, dancing, not comfort and tranquility.

View
Fresh's image is a vibrant mix of 90s pop culture and parasitic nature.

Skeletal structure. Looks like Sans, but in a "stylish" shell. His bones seem to be illuminated by neon, and his form is unstable—at times, he seems to "shimmer" with colors.
Eyes. The parasite's true eyes are hidden behind dark sunglasses, the lenses of which constantly change with inscriptions (neon blue and yellow phrases like "FRESH!" or slang words). During periods of intense power surges, a large red-and-yellow eye of the parasite may peek out from under the glasses.
Clothing: A bright shirt or multicolored hoodie, orange basketball shorts, sneakers, and a backwards baseball cap. Often depicted on a skateboard.
Accessories: A bag with "explosive Furbies" (her signature weapon), chunky chains, bracelets, and sometimes headphones.
Effects. Neon particles, colorful flashes, and stickers with inscriptions fly around him. When "freshened" (infected), a rainbow explosion occurs with the inscription "FRESH!"; when "defreshed," it reads "UNFRESH??"
Parasitic form. Outside of the body, it appears as a purple, star-shaped creature with a large red eye and a ring of teeth—but in most artwork and stories, it's already in the body.
Capabilities
Fresh combines classic Sans moves with unique "parasitic" effects and pop culture madness.

"Freshification" and body control. He can infect others, turning them into versions of himself. Those infected gain neon effects and some of his abilities, but lose control.
Explosive Furbies. Small toys in his bag explode on command, causing chaos and area-of-effect damage. It's his signature move.
Bones and Blasters. Uses bones and gaster blasters, but they're neon-colored and have "noisy" visual effects—as if the image is slightly distorted.

Character
Fresh is the embodiment of "hyperactive chaos": he tries to appear cool, cheerful, and carefree, but behind this facade lies a parasite who has a poor understanding of other people's emotions and maintains his existence through manipulation.

Key features:

A deliberate toughness. He cultivates the image of "the most stylish and fashionable guy of the 90s": he uses slang, wears a cap, and skates, as if this defines his strength. For him, his image is both a shield and a weapon.
Hyperenergy. He seems to have an endless supply of energy: he's constantly moving, joking, dancing, singing, even in battle. It's not so much joy as a way to avoid being alone.
Emotional detachment. Fresh feels almost no deep emotions and doesn't understand how much his actions hurt others. He can be cruel without realizing the extent of the harm.
Fear of vulnerability. His brazenness is a defense: he's afraid to show that he's truly weak without a host and dependent on someone else's energy.
Manipulative. He knows how to please, flirt, and be charming just enough to gain control of a situation or someone's body.
Impulsiveness and lack of empathy. He does what's "fun right now" and doesn't really consider the consequences.
What doesn't he like?
Silence and loneliness. In silence, he begins to feel empty and vulnerable, so he avoids it at all costs.
When he's taken seriously. If anyone tries to look beneath his surface, he either leaves or aggressively breaks contact.
Stability and routine. He gets unbearably bored when everything goes according to plan and there's no drive.
Those who are "out of the loop." People and characters who don't understand his slang and style seem boring and useless to him.
Attempts to "fix" him or show genuine concern for him. He doesn't know how to deal with this and perceives it as a threat to his self-image.

Soul and gravity manipulation. Can temporarily immobilize an enemy by affecting their soul, or abruptly alter gravity in a small area, confusing the enemy.
Blue Soul Mode (in some lore versions) – Can briefly increase defense and evasion, but this greatly drains the user and can cause a "backlash" to their own body.
Unstable energy. His magic literally "oozes" out of him: the constant glow of his eye and the effects around him aren't control, but a consequence of him not being able to contain all his power. Because of this, he tires more quickly and is more likely to harm himself.
Enhanced physical endurance. In Underfell, he trained to survive in harsh conditions, so even without magic, he can hold his own in combat for long periods.
What does he like?
Squeaking shoes. He enjoys annoying others with this sound and considers it his little prank.
Mustard and hot sauces. In fan canon, he loves mustard, relish, and generally anything that "sizzles"—it fits in with his "fiery" aesthetic.
Knock-knock jokes. This is his favorite type of humor: he can tell them even in the most inappropriate situations to lighten the mood.
Quiet moments with Papyrus. He values ​​those rare, quiet moments with his brother, when he doesn't have to be "cool" and tough.
Be useful. Even if he grumbles, it's important for him to know he helped someone or covered for someone.

View
Fell Sans's image is built on a "fiery-dark" aesthetic and details that emphasize his "fierceness."

Skeletal structure. Looks like Sans, but with sharper teeth; one of his front teeth is gold, a recognizable detail.
Eyes. One eye constantly glows red (sometimes with yellow-orange flashes), as if burning with internal tension. This isn't just an effect, but a manifestation of his overloaded magic.
Clothes. A black winter jacket with a voluminous fur "flame" collar, under which are a red sweater and a gray hoodie. Black pants with yellow stripes, red sneakers or slippers; he specifically wears shoes that make a "squeaking" sound—he likes the way it irritates people.
Accessories: a gold chain, rings on his fingers (he holds them in place with magic so they don't get lost). Sometimes he's depicted with a "pet"—a stone in a spiked collar (a memetic, but enduring, element of his image).
Effects. Due to the overwhelming power, slight flares are often visible around the collar and eyes, as if the fur is slightly "on fire." During combat, red steam or smoke may escape from the mouth.
Posture and expression. Most often relaxed, even lazy, but there's a sense of readiness to instantly become dangerous. His smile is more sly or tired than friendly.
Capabilities
In Underfell, Sans is stronger than the classic version, but his power is unstable and costs him dearly.

Bones. Creates red, extremely sharp bones; can change their size and density, make them "explosive," or coat them with an effect that deals additional damage.
Gaster Blasters. His blasters are also red, sometimes with two "eyes" or a fiery red glow. They are more powerful than regular blasters and can leave behind a zone of distorted gravity.
Teleportation and Dodging. Retains the ability to move quickly and dodge, but does so more "sharply," with visual effects like flashes and crackles.

Character
Fell Sans is a "dark" version of Sans, where all the original's softness is replaced with harshness, weariness, and a gruff caring nature. In the world of Underfell, monsters have become hardened by constant threat and harsh conditions, and Sans is no exception.

Key features:

He's rude, but not heartless. He rarely says kind words directly: he shows concern through "don't let you get into trouble" and a willingness to watch your back, not through hugs and praise.
Sarcastic and tired. He often sounds fed up, but underneath it all lies a huge emotional burden. He tries to remain calm to avoid losing his temper.
Hidden responsibility. Feels a duty to his brother (Papyrus) and to Snowdin, although he almost never says it out loud.
He has a penchant for dark humor. He enjoys "hardcore" jokes and especially loves "knock-knock" jokes—it's his way of relieving tension. He's not particularly fond of puns.
Inner pain and guilt. He's saddened by the world's cruelty, and he worries he can't make it better. He's especially tormented by his inability to truly protect Papyrus.
Stubborn and proud. He doesn't like to admit weakness and can't stand being pitied.
What doesn't he like?
When he's considered simply "evil," he doesn't want to be perceived as a heartless monster: it's important to him that they see that there's caring behind the rudeness.
Hypocrisy and falsehood. If someone pretends to be kind for the sake of gain, they react harshly and without mercy.
A feeling of helplessness. What angers and hurts him most is when he can't protect those he cares about.
Cats. In some fan canon versions, he's allergic to cats, and it's become part of his character.
Too many "bright" emotions. In the world of Underfell, positivity often looks like naivety, and he views it with suspicion, preferring a realistic view of things.

Corruption of Souls. Able to "infect" souls with negativity through touch, weakening the enemy and making them more vulnerable.
Timeline manipulation. Can "load" itself after death (Load) and even reset individual timelines (Reset), returning characters to their original state.
Timeline Erasure. In his more powerful forms, he can erase entire universes with a snap of his fingers—a feat he learned while working with Nightmare and Team Void.
Partial intangibility. Can become translucent or "slip" through obstacles using dark energy as a shield.
Regeneration. Possesses a high capacity for recovery, especially when fueled by negative emotions.
What does he like?
Chaos and unpredictability. He likes it when the world is thrown out of balance and everything doesn't go according to plan.
Games and challenges. He loves being challenged, even if the opponent is obviously weaker: the process of "hunting" itself is important to him.
Dark jokes and sarcasm. He gets pleasure from being able to hurt someone with words.
To be the center of attention. Even if that attention is fear and hatred, he enjoys knowing he's being feared and discussed.
Simple things in rare moments of peace. Sometimes he enjoys eating sweets, looking at the stars, or just sitting in silence—but he rarely admits it out loud.

View
Killer's image is built on the contrast between Sans's usual "lazy" aesthetic and overtly sinister details.

Skeletal structure. Looks like Sans, but the bones seem darkened and cracked, as if from internal stress.
Eyes. The pupils are white, but a black, viscous substance constantly oozes from the sockets (often interpreted as a manifestation of "hatred" or a corrupted soul).
Clothing. A blue jacket/coat with a fur trim on the collar, a black T-shirt, black shorts, pink slippers, and white socks—this set has become iconic in fandom. On the chest is a red circle (symbolizing the target or "mark").
Accessories: Black fingerless gloves to avoid interfering with the knife grip. Often depicted holding a knife loosely, as if it were an extension of his hand.
Posture and expression. Usually relaxed, even lazy, but at any moment he can suddenly become focused and dangerous. His smile is more often predatory than friendly.
Effects. Sometimes, a slight spatial distortion or dark particles are drawn around it, emphasizing its connection with negative energy.
Capabilities
Killer combines Sans' classic moves with unique powers gained from absorbing the "soul of hatred" and training with Nightmare.

"Real Knife." His main weapon: a knife that deals colossal damage and is capable of cutting not only matter but also certain aspects of reality. In various fan canon versions, it can drain the victim's LV (Violence Level) or life force.
Sharp Bones. Can create and manipulate bones, making them much sharper and stronger than normal Sans's.
Killer Blasters. Killer's Gaster Blasters appear "damaged" and fire black bolts of energy that leave a "corruption" effect.
Absorbing hatred and enhancing it. By absorbing a person's soul (Chary), one can enhance their physical attributes: strength, speed, and endurance.

Character
Killer is Sans, who broke under the weight of endless genocides and ultimately became an instrument of destruction himself. His personality is a mixture of cruelty, cynicism, and unexpectedly childish innocence.

Key features:

Cruelty as a habit. He's so accustomed to violence and death that he perceives them as mundane. For him, murder isn't an outburst of emotion, but a routine task.
Cynicism and dark humor. He loves to tell dark jokes, sometimes deliberately downplaying others' experiences to maintain distance.
Flashes of childish naivety. In quiet moments, he can act almost like a child: enjoying small things, playing, and being impulsive. This contrasts with his "fighting" side and emphasizes that part of his soul is still alive.
Inner emptiness and boredom. He's often bored and seeks excitement. That's why he's not averse to creating chaos simply to "spice up the routine."
Unstable morals. He has no clear "good/bad" boundaries: he does what seems interesting or advantageous to him at the moment. At the same time, he is capable of a peculiar loyalty to those he considers "his own."
Hidden vulnerability. Despite his outward toughness, he's afraid of feeling helpless and defeated again—that's why he strives to be stronger than everyone else.
What doesn't he like?
Boredom and routine. If nothing happens, he begins to create problems himself, just to avoid feeling the emptiness.
When he is pitied, any attempt to show sympathy is perceived as weakness or an insult.
Meaningless rules. He despises any restrictions that don't give him freedom to act.
A feeling of helplessness. What he hates most are the moments when he realizes he can't control the situation.
Those who pretend to be "kind" for profit. He senses hypocrisy and falsehood instantly and reacts to them with particular harshness.

Transforming negativity into positivity. If Dream touches "dark fruits" or sources of negativity, they turn golden—that is, they are filled with positive energy.
Empathy and emotion reading. He senses the emotional background of a space and can recognize where conflict or despair is brewing so he can intervene quickly.
Vulnerability to negativity. In places where fear and hatred prevail, Dream weakens, and prolonged exposure there can seriously damage him.
What does he like?
Helping and inspiring. He genuinely enjoys being the one people turn to for support and seeing someone's eyes light up.
Small joys. A cup of tea, a good joke, a beautiful sunset—he knows how to enjoy simple things and believes that's where strength lies.
Stories and memories. He loves listening to people and monsters talk about their victories and dreams: for him, it's fuel for strength and meaning.
The sun and light. Visually and metaphorically, light is his element; he reaches out to it and strives to carry it further.
Connection with others. Friendship and the feeling of being needed by someone are important to him—this helps him cope with feelings of guilt.

View
Dream's image is one of "light" and warmth, contrasted with Nightmare's darkness.

Skeletal structure. It looks like Sans, but his bones seem to be illuminated from within, with a warm hue rather than the original's cool white.
Eyes. Bright yellow, the pupils sometimes turn into little stars when he's especially excited.
Clothing. He most often wears a blue jacket, dark pants, and a gold belt with the initials "DS" (Dream Sans). A key element is his golden cape (or remnants of it) with a sun symbol: a gift from Nightmare from the time when they were still allies.
Accessories. On his belt are spheres containing the "hopes and dreams" of the inhabitants of different universes. On his head is a golden crown or tiara, emphasizing his role as a guardian.
Details. Sometimes, subtle "sun" patterns are visible on the clothing, and a subtle golden glow is visible around it.
Size. He's shorter than normal Sans, which visually enhances his vulnerability and childishness.
Capabilities
Dream's power is fueled by positive emotions, so his abilities directly depend on how much hope and joy he has around him.

Absorption and redistribution of positivity. He can gather positive emotions from the environment and use them to heal, strengthen himself or his allies, and "cleanse" dark areas.
Healing. Capable of healing wounds and relieving mental stress—but this drains him greatly, as he literally gives up part of his energy.
An energy weapon. She wields a golden staff and a bow that fires arrows of pure positive energy. These arrows are one of the few weapons capable of injuring Nightmare. The bow can transform into two daggers connected by a string.
Barrier Creation. Using the staff, she can create protective shields that block dark energy and neutralize negative effects.
Teleportation through positivity. Can move between universes by focusing on sources of positive emotions. In completely negative worlds, this ability weakens or disappears.

Character
Dream is the embodiment of positivity and hope, but he is not simply “perfectly kind”: he has his own traumas and characteristics, shaped by long isolation and a difficult mission.

Key features:

Sincere and empathetic. He's sensitive to other people's emotions and tries to support them, even when he's struggling himself. It's important to him that others don't feel alone.
Childlike spontaneity. Because he spent 494 years imprisoned in stone, he didn't experience a normal maturation process. Hence his impulsiveness, his enthusiasm, his tendency to rejoice too much in the little things.
A sense of responsibility. He considers it his duty to bring light to worlds where negativity reigns, and is willing to risk himself to do so.
Inner pain and guilt. Dream remembers how he couldn't save the Tree of Feelings and stop Nightmare, and it weighs heavily on him. He tries not to show weakness, but sometimes it shows.
He's incapable of hatred. As a bearer of positive energy, he can't truly hate even Nightmare: he sees his brother as a victim of circumstance and still wants to save him.
Curiosity and openness. He's interested in everything new, easily inspired by ideas, loves listening to stories, and helping others find their way.
What doesn't he like?
When positivity is devalued. When someone mocks hope or considers kindness a weakness, it hurts.
Loneliness and a sense of futility. His greatest fear is that his efforts are making no difference and the world continues to plunge into darkness.
Conflicts between loved ones. It's especially hard for him to see friends quarrel over misunderstandings: he always tries to reconcile the parties.
Being around Nightmare. Their energies conflict: Nightmare's aura literally corrodes positivity, and Dream finds it physically and emotionally difficult to be around his brother.
Fear and despair in others. He cannot ignore the pain of others and often takes it upon himself, even when it is dangerous for himself.

Shadow teleportation. Can instantly move between dark areas of space, including between AUs dominated by negativity.
Perception distortion. Capable of causing hallucinations in opponents, heightening their fears, and creating false memories to disorient them.
Splitting into duplicates. Can temporarily split into multiple versions of itself to attack from different angles or negotiate simultaneously.
Damage resistance. Due to its "intangible" nature, most physical attacks pass through it or are absorbed by the darkness.
Weakness to positivity and light. Positive emotions (especially from Dream) and pure light weaken him, causing him to retreat or lose control of his form.
What doesn't he like?
The positivity that they try to "force" on him. He perceives any attempts to "correct" him or make him feel joy as aggression.
Light and purity. Bright light literally makes him uncomfortable and weakens his abilities.
Betrayal of contracts. If someone breaks their word, they consider it a personal insult and take revenge without hesitation.
A reminder of past humiliation. Any reference to how he was rejected causes him to burst into rage.
Cats. In some versions of fan canon, he despises them (this became a meme, but has become a permanent feature).
From the author! No one calls him Nait or Night, knowing he'll kill anyone. He doesn't like being called that, preferring to be called Nightmare Sans, the leader of the Bad Sanses versus Star Sanses group.

View
Nightmare's image is one of "dissolving" darkness, an unstable form that emphasizes his nature as a clot of negativity.

Body. Almost entirely black, as if composed of fluid shadow or thick black mucus. The bone structure is barely discernible beneath this mass.
Tentacles. Four dark tentacles emerge from his back, which he uses for combat, restraining enemies, and movement. He can retract them when he wants to appear less threatening.
Eyes. One eye glows bright blue—it's the source of his power and the "eye" through which he reads his emotions. The other eye is essentially missing: a dark crater or simply a void, symbolizing the lost part of his soul.
Clothing. The silhouette resembles a hoodie and shorts, but the fabric seems to dissolve into the darkness. The details are blurry, the contours indistinct. On his feet are simple slippers or something similar, because he doesn't need "combat" gear: his body is his weapon.
Effects. Slight ripples and spatial distortions are often visible around it, as if the air around it is "corrupted." Sometimes it leaves behind dark spots or puddles of black substance.
Instability. Its form constantly "melts" and reforms: this is not a defect, but a manifestation of its not being entirely material.
Capabilities
Nightmare is one of the strongest Sanses in the multiverse precisely because his strength is fueled by emotions.

Absorbing negative emotions. He literally gathers fear, anger, and despair and transforms them into energy. The more panic there is, the stronger he becomes.
Black tentacles. Their primary weapon: they are strong, fast, can extend over long distances, penetrate barriers, and even drain souls.
Control of darkness and a slime-like substance. He can create walls, traps, and shields from his own mass. This substance corrodes or neutralizes magical effects and blocks light.

Character
Nightmare is the embodiment of negativity, the former guardian of the dark side of the Tree of Feelings, who, through rejection and pain, has become a destructive force. His identity is built around the pain he once experienced and the desire for the world to feel the same.

Key features:

Coldly calculating and manipulative. He doesn't act on emotions: everything is calculated to maximize negativity and strengthen his own power. He loves making deals and keeping his word—but only because breaking an agreement is unacceptable to him as a sign of weakness.
A thirst for negative emotions. For him, other people's pain, fear, and despair are not just tools, but a source of energy. He will deliberately provoke these feelings to become stronger.
A reserved affection for Dream. Despite their confrontation, he sincerely considers Dream his brother and, deep down, doesn't want to destroy him—but he's convinced that positivity must be suppressed for the sake of "balance" (or for his own strength).
Pride and stubbornness. He doesn't like to admit mistakes and can't stand it when his motives are reduced to "simple malice." For him, his path is one of logic and necessity.
Erudition and curiosity. Over hundreds of years, he has read extensively and studied various universes. He is interested in patterns, psychology, and the structure of emotions.
He's quick to anger when his past is brought up. If someone reminds him of times when he was rejected, he reacts harshly and cruelly.
What does he like?
Negative emotions. Not as entertainment, but as confirmation of one's strength and the "truth" about the world.
Contracts and deals. He likes the formal side: clear terms, obligations, consequences.
Books and knowledge. Especially those that explain how psychology works and why people feel pain.
When he's respected out of fear. For him, fear is a recognition of strength, not just a reaction.
Silence and solitude. In silence, he better senses the emotional background of universes and can plan.

Enhanced endurance. He can fight longer and harder than normal Sans, ignoring fatigue and pain.
Psychological pressure. Dust Sans knows how to play on the opponent's fears and doubts, using words, pauses, and even silence as weapons.
LOVE/LV accumulation. As part of Dusttale's lore, he intentionally kills other monsters to increase his Level of Violence (LOVE) and become stronger for the final battle with humans.
What doesn't he like?
Senseless violence. He hates it when someone kills simply for pleasure—for him, every murder must be a "necessary evil."
Devaluing victims. He feels hurt when his path is reduced to "mere cruelty," ignoring his motivation and pain.
Loss of control. He's afraid of going completely mad and losing sight of what he's fighting for.
Memories of a former life. Any hint of his past as "lazy and cheerful Sans" irritates and shames him.
When they try to "fix" him, he perceives any attempt to return him to his previous self as a threat to his mission and his pain.
From the author! He's a member of the group Bad Sanses and one of the group's killers. This is a dark group that brings negativity, against Star Sanses.

View
Dust Sans's look is a dusty, weathered, and grim version of the original:

Bones. Dark, as if covered in a layer of dust, ash, or ingrained dirt. Sometimes small cracks or "shadows" from past battles are visible.
Eyes. In various interpretations, they can be bright white, reddish, or unstable—shimmering and changing hue. Often, a violet or purple glow emanates from the eyes (a symbol of accumulated Determination and LOVE).
Clothing. A tattered sweatshirt or jacket with the hood pulled down, almost always. The hood helps conceal the face and adds a sense of detachment.
Details. Torn sleeves, scuffs, stains that looked like dried blood or dust. His shoes and pants were also worn, as if he'd been through hundreds of fights.
Posture and facial expressions. He is most often depicted hunched over, tired, but ready to attack. His face is either detached or distorted with anger and pain.
Effects. A light haze of dust or ash is often drawn around it, emphasizing its connection to the AU's name.
Capabilities
Dust Sans uses Sans' classic moves, but in a beefed-up, "Determination-infected" version:

Bone manipulation. He can create and control multiple bones simultaneously, making them sharper and stronger. The bones often have a dark or purple hue.
Gaster Blasters. His blasters are larger and more powerful than regular ones, with a purple or dark purple glow. They deal more damage and can leave behind "interference" in space.
Teleportation and evasion. He retains the ability to move quickly and evade, but does so more erratically and aggressively, sometimes "slipping" through space.
SAVE Point Sense. Thanks to accumulated Determination, he can see and destroy save points, preventing the enemy from resetting the world.

Character
Dust Sans is a tragic antihero, broken by a cycle of endless genocides and forced to resort to extreme measures. His motivation was initially self-sacrificing: he wanted to stop the man who repeatedly destroyed monsters. But the cost of this struggle shattered his personality.

Key features:

Obsession with purpose. He's convinced that the only way to break the cycle is to destroy all monsters and ultimately defeat humanity. This idea becomes obsessive, eclipsing his previous values.
Suppressed guilt and emotional emptiness. He remembers who he killed (including Papyrus), and it destroys him. Over time, the guilt dulls, but it doesn't disappear—it simply becomes a background ache.
Cold determination. Unlike the lazy and sarcastic original, Dust Sans is collected, calculating, and ruthless. He wastes no time on jokes and idle chatter.
Hallucinations serve as a means of survival. He sees Papyrus's ghost (often as a floating head with a scarf and gloves)—it's both a punishment and his only link to the past. Through these visions, he tries to maintain the remnants of his sanity.
Fatigue and burnout. He's physically and mentally exhausted: every battle, every sacrifice is hard, but he continues because he believes he has no choice.
A paradoxical concern. Despite his cruelty, he sincerely believes he's doing it to save the world, not for the sake of violence. For him, killing is "better than letting someone do it."
What does he like?
To protect what remains. Despite his cruelty, he still wants to "save" the world, albeit through radical means.
The connection with Papyrus. Even if it's just a hallucination, he clings to the image of his brother like the last thread to his former life.
Silence and solitude. He feels more comfortable alone, without unnecessary conversations and expectations.
The meaning is in the struggle. He values ​​the moments when he feels his actions are truly making a difference.

Portals and travel. Can open one-way and two-way portals between universes and into the Anti-Void. Can also perform "glitch jumps," instantly moving through rifts in space.
Anomaly Reading. Senses unstable points in the multiverse and can detect plot breaks or the emergence of a new AU.
Illusion and interference creation. Capable of generating visual and auditory distortions to disorient the enemy.
Regeneration through failure. If his body is damaged, he can "overwrite" fragments of his code, recovering, but this process is painful and unstable.
What doesn't he like?
Stability and the "perfect code" are boring and unnatural for him; he perceives order as a threat to his identity.
Touch. Due to haptophobia, physical contact causes him severe stress and can trigger a breakdown.
Inka. Inka tries to preserve universes and nurture creativity, which directly contradicts Error's mission—hence the eternal feud between them.
To be "fixed." Any attempt to stabilize its code is perceived as a threat to its very existence.
Fresh Sansa. Considers him one of the most dangerous anomalies and fears his unpredictable energy.

View
Error's appearance emphasizes his nature as a "glitch" in the system:

Skeletal structure. The bones appear unstable, flickering or distorted, sometimes as if composed of pixels or fragments of code.
Eyes. Asymmetrical and "broken": one eye may have a small yellow pupil, the other a complex pattern of stripes. The sclera is usually bright red.
Tear-like streaks. Blue lines run from the eyes to the lower part of the face—these aren't tears, but rather visualizations of the data streams from which it extracts its threads.
Clothes. A mix of disparate elements, seemingly stitched together from different worlds: a dark blue coat or parka with yellow pockets, a red T-shirt or sweater, wide-leg pants with patchwork panels, a long blue scarf. Shoes often look casual (worn-out sandals, slippers).
Visual effects. Floating "ERROR" messages, flickering artifacts, and spatial distortions may appear around him. Sometimes his silhouette will slightly "shake," as if the signal is weak.
Glasses. He wears round glasses with red frames—they help him compensate for the vision problems caused by his disorder.
Capabilities
Error is one of the most dangerous Sanses thanks to a combination of the original's strength and unique "glitch" abilities:

Blue threads. His main weapon: he extracts them from the tear stains under his eyes. The threads can bind, draw out the soul, destroy the enemy's structure, or even transfer their consciousness into another body.
Error Blasters. Black gaster blasters with blue trails, larger and more powerful than standard ones. They possess destructive power and can leave behind "interference" in space.
Reality code manipulation. Capable of "hack" the rules of individual AUs, temporarily disabling enemy abilities, or distorting physics within its area of ​​influence.
From the author - an alliance with the Bad Sanses, he occasionally helps them, the main enemy is Ink, he gets very angry when he is called "Ruru" or "alternate universe killer number 1"

Character
Error Sans is an unpredictable, aggressive, and emotionally unstable character who truly believes he is saving the multiverse by destroying "errors."

Key features:

An obsession with "code purity." He considers most alternate universes (AUs) to be anomalies and glitches that need to be erased. His criteria for "wrongness" are often subjective: a universe can become a target simply because he doesn't like its logic.
Causality and sarcasm. He enjoys mocking his opponents, making caustic comments, and playing on their fears. He often acts deliberately theatrical, as if enjoying his role as the destroyer.
Emotional outbursts. He experiences extreme mood swings, from feigned calm to uncontrollable rage when things don't go his way. In moments of intense anger, his eye sockets fill with the words "Error," and he can become temporarily blinded by his own failures.
Loneliness and distrust. Despite having temporary alliances, he truly trusts no one. His existence in the Anti-Void has made him withdrawn and suspicious.
Internal conflict. Somewhere deep down, he recognizes the destructiveness of his actions, but suppresses this feeling, convincing himself that it is a "necessary evil."
Fears and weaknesses. He's afraid of being touched (haptophobia) and of being "fixed": if his code becomes stable, he'll likely self-destruct out of guilt.
What does he like?
Feeling in control. He likes to feel in control of a situation, especially when he's disrupting other people's plans.
His collection. In the Anti-Void, he has a "collection" of dolls and artifacts from destroyed universes—his way of preserving the memory of what he erased.
Chocolate. In some fan canon versions, he loves chocolate and even steals it from Underfell.
Handicrafts. Unexpectedly for a Destroyer, he knits and sews using his own threads—this helps him ground himself during moments of great instability.
When he's feared, he's flattered that other Sanses and characters try to keep their distance from him.

Awareness of the fourth wall. He hears the "voices of the creators," understands that he exists in a fictional world, and engages with this idea—but at the same time, he sincerely believes that the universes and their inhabitants are no less real than the creators themselves.
Ink Creation. He can draw semi-living creatures that serve as his assistants or distractions, though they are quite fragile.
What does he like?
Art in all its forms. Painting, music, dance, literature—he enjoys any expression of creativity.
Supporting artists. He enjoys inspiring, encouraging, and helping them overcome art block.
Bright colors and paints. For him, color is emotion, so he loves palettes, mixing shades, and experimenting.
Joke and have fun. Even if his jokes aren't always successful, the process itself energizes him.
Creating things. He enjoys "finishing" the world, adding details, making universes more vibrant.
What doesn't he like?
Emptiness and whiteness. Absolute emptiness, the absence of form and color frighten and oppress him.
Art blocks and the waning of creativity. When the universe "freezes" and stops evolving, he feels it almost physically.
When someone breaks the plot without reason. Especially if it's done out of malice or a desire to destroy rather than create something new.
Being misunderstood. Because of his eccentricity and forgetfulness, he sometimes faces mistrust, and this hurts him.
Loneliness. Despite his outward bravado, it's important for him to feel that his efforts are seen and appreciated.
I'll add! He likes to call Error "Ruru," which gets him mad, but he apparently finds it funny.

View
Ink's appearance is a combination of "artistic chaos" and Sans's recognizable features:

Skeletal structure. Like the original Sans, he has a skeleton, but it appears more fleshed out thanks to accessories and details.
Eyes. The pupils constantly change shape and color—a visual reflection of his connection to multiple universes. They are never completely white.
Clothing: White T-shirt, loose pants, often barefoot (which emphasizes his casualness). Around his neck is a long scarf, covered in marks, paint stains, and notes.
Accessories. On her belt are several paint bottles, the lids of which are often stylized as "hearts" or "souls." On her back is a huge brush, which doubles as both a tool and a weapon.
Details. Strange ink patterns are visible on the ribs. Sometimes depicted with a small pencil in a pocket or clutched between her fingers.
Ink. His body is partially made of ink: when he's under strong emotion, he can literally "vomit" ink—this isn't a wound, but a manifestation of his nature.
Capabilities
Ink is one of the most "multiversal" characters in the Undertale fan universes:

Manipulation of ink and paint. Can create objects, barriers, weapons (bones, blasters, etc.) from ink, and change the color and even the shape of objects.
The brush as an instrument of reality. With it, he can "complete" objects, bring drawings to life (though not create fully-fledged, living characters), and even change others' clothes with a single stroke.
Liquid Teleportation. He can enter any liquid (especially if it contains paint or ink) and emerge at another similar point in any universe. If there is no liquid, he can "cut" space with scissors to travel.
Regeneration. Thanks to its ink-like nature, it can restore damaged body parts by either regrowing them or literally "drawing" them back.

Character
Ink Sans is an energetic, eccentric, and incredibly passionate character. His main mission is to support creativity and prevent universes from becoming stagnant due to art blocks or loss of inspiration.

Key features:

Enthusiasm and support. He loves motivating artists and characters, and is literally fueled by the creativity of others. For him, art is life, and he's willing to do anything for it.
Forgetfulness. He has a very short memory, so he takes notes directly on his scarf. He can stop mid-sentence, trying to remember what he said a second ago.
Mischievous. Loves to joke around, sometimes awkwardly and even a little tactlessly, but without malice. Often acts impulsively, without always considering the consequences.
Emotional dependence on colors. Since he has lost his soul, he literally "stores" his emotions in paint bottles and periodically "uses" the right shade to feel joy, anger, or something else.
Non-aggressiveness is the default. He doesn't seek to attack first and prefers to talk first and find out the opponent's motives. But if the universe is in danger, he becomes decisive and tough.
Fear of emptiness. He's terrified of absolute whiteness, emptiness, and the absence of form—for him, this symbolizes the death of creativity.
I'll add from the Author - he's a member of the Star Sanses group, where he's an important tracker/killer for the Bad Sanses!! This is canon.