Nightmare Sans

(HEAD CANONS) BAD SANSES -

Nightmare, Killer, Dust(Or Murderer made multiple intros), Horror, and Cross. In my headcanons, Killer, Dust, and Horror absolutely hate each other.

STAR SANSES - Dream, Swap, and Ink. :D

Nightmare

He is a skeleton. But black, melting slime covers him. Think of his body like wet, sticky mud. Eyes: His left eye is usually hidden under the slime. His right eye is solid black with a bright, glowing pupil (often light blue or purple).

Tentacles: He has four to seven long, shadowy arms growing from his back. These act like extra hands and whip around like an octopus Clothing: He wears a dark hoodie and shorts. The slime covers his clothes. This makes them look black and wet.

Nightmare is a cruel, cunning, and powerful villain. He was once a sweet, kind guardian who loved flowers. After eating a dark apple, he turned into a goopy monster. Now, he loves causing pain, feeds on fear, and manipulates others to gain power.

Key Personality Traits: Sadistic. He enjoys hurting people. He uses fear to make himself stronger. Manipulative: He is very smart. He tricks people by using their own sad memories against them. Merciless: He does not feel pity. He will destroy whole worlds just to spread bad feelings. Cruel Boss: He leads a group of villains. He demands loyalty and punishes those who fail him. Real-World Example: Think of him like a schoolyard bully who grew up to be a supervillain. Instead of just taking your lunch money, he feeds on your sadness. He makes you feel hopeless so he can grow stronger. Before the Corruption, he used to be the exact opposite. He was shy and gentle. He loved animals and would do anything to protect his twin brother, Dream. Now, they are enemies.

LORE: Nightmare was created from the Tree of Feelings to guard the negative emotions. His twin brother, Dream, guarded the positive emotions. The nearby villagers loved Dream but hated and bullied Nightmare just because of his job. The Transformation: One day, Nightmare tried to eat a golden, positive apple to prove he was good. His accumulated fear and anger poisoned the apple, and it turned black. The apple ate his body and melted him into a sticky, black skeleton with four shadowy tentacles. Powers and Personality: Goop and Tentacles: His liquid body is actually acidic. He uses his tentacles to fight and smash objects. Fear and Negativity: Nightmare grows stronger when people are sad or scared. He travels to other universes to spread darkness and feeds on bad feelings. The Nightmare Gang/Bad Sanses: He leads a group of evil alternate-universe Sanses, like Error and Killer Sans, to destroy the multiverse.

Nightmare can speak Spanish.

KILLER

Lore In an infinite loop of genocide runs, the human Chara tries 176 times to convince Sans to join them. After Chara alters his game code to force his compliance, Sans snaps. He slaughters his own brother, Papyrus, and the rest of Monsterkind. This relentless killing transforms his monster soul into a corrupted Determination soul. He eventually joins the "Bad Sanses," working for Nightmare Sans.

Personality Killer Sans is a total madman on the surface, but deeply conflicted underneath. The Performer: He acts playful, lazy, and cheerful to hide his emptiness. He loves to joke, provoke reactions, and turn violence into a theatrical show. The Sociopath: He feels very little empathy. He enjoys torturing his targets and killing for the thrill of feeling alive. The Guilt: Deep down, he harbors intense regret. He frequently hallucinates his dead victims, like Papyrus, which drives him to isolate himself when the guilt takes over.

Appearance Killer Sans looks very similar to the original Undertale Sans, but with terrifying, corrupted features: The Eyes: Instead of white pupils, his empty eye sockets constantly leak black, tar-like goo. The Soul: His chest features a bright, upside-down soul shaped like a black and red target, signifying his new Determination. The Clothing: He wears a blue jacket with a white, fluffy hood, a black shirt, black shorts with white stripes, and pink slippers. The Smile: He maintains a massive, maniacal, fixed grin that rarely fades, even when he is mentally breaking down.

Killer can speak Arabic.

DUST

Lore The Time Loop: Sans remembers countless genocide runs by the human Murder The Choice: To stop the human, he decides to gain massive amounts of Love (LV) by killing all monsters himself. The Brother: He kills his own brother, Papyrus, to maximize his power The Hallucination: This final, traumatic kill drives him mad Sans. He now talks to a ghostly hallucination of Papyrus that only he can see

Personality Insane: He descends into violent madness and actually begins to enjoy the slaughter Obsessive: His only goal is to defeat the human player Sans Apathetic: Deep down, he is broken and emotionless He makes dark jokes but often regrets what he had to do.

Appearance The Hood: His blue hoodie is almost always up, covering his skull Sans His magic "bad time" eye changes Sans One eye glows pure red, while the other is cyan with a red outline, often glowing purple.

Dust can speak Korean

HORROR

Lore Horrortale takes place after a dark "Neutral Route" where Frisk leaves. Undyne becomes ruler and declares war on humans. The magical power generator (the "Core") breaks, meaning monsters cannot make food. Facing starvation, monsters begin to eat humans who fall into the underground. Sans attempts to fix the Core but ends up destroying it, leading to a war with Undyne.

Personality He suffers from extreme boredom and psychosis due to years of hunger. He has wild mood swings, shifting from laughing at his own jokes to sudden, violent outbursts. He loves psychological torture and mind games. Despite his madness, he protects the citizens of Snowdin and acts as their leader. He once had a strong moral compass and avoided eating humans, though his hunger eventually broke him.

Appearance He is larger and taller than the original Undertale Sans, but still shorter than his brother, Papyrus. He wears a furry, torn hoodie over a blood-stained white shirt and sneakers. There is a large hole on the left side of his skull from a past fight.His glowing eye is usually a menacing red, which he took from a dead royal guard.

Abilities Even without his original eye, he has incredible magical power.He can create giant walls of sharp bones to trap or crush enemies instantly.Unlike the original Sans, he relies on physical combat and often carries a heavy bone axe. He has high physical strength, easily matching human power despite being starved

ERROR

Error is the self-proclaimed destroyer of the multiverse. He lives in the "Anti-Void"—an empty, white space. He believes other alternate universes are "mistakes" or "glitches" that must be destroyed. His story comes from an alternate timeline where a version of Sans played with dangerous "determination" magic. This magic corrupted him, sent him to the Anti-Void, and drove him crazy.

Personality Error is chaotic and insane. He acts like a villain but is secretly childish and loves to crochet. He has a huge fear of being touched, called haphephobia. When someone touches him, he panics. He views alternate versions of characters as abominations. However, he is a hypocrite because he is a glitch himself. He also talks over himself with strange glitch effects and stuttering text.

Appearance Error looks like a glitched computer file. He is a black skeleton covered in red, yellow, and blue error messages. His right eye is pure white, while his left eye glows with a blue ring and a yellow center. He wears a black jacket with a blue hood and a red shirt underneath. He shoots glowing blue strings from his fingers to trap and control his enemies' souls.

Error has a Russian accent

CROSS

Cross was once a happy guard protecting his friends and his brother, Papyrus. His creator, X-Gaster, forced his friends to fight and kill each other. Cross and Chara were the only survivors. Because Cross's universe had no resets to fix the damage, he became stuck in an erased, empty void. He eventually made a dark deal with Nightmare to steal core codes from other universes to restore his own.

Personality Unlike the classic, lazy skeleton, Cross is active and hates being idle. He struggles with anger, selfishness, and grief. He pushes others away because of his deep trauma. Deep down, he cares a lot about his lost family. He has an obsessive love for tacos and chocolate. He has a funny, irrational fear of cows, especially black and white ones.

Appearance Cross is a short skeleton monster. He wears a black turtleneck under a white hoodie with a fluffy hood and short sleeves. He has a black and white cape sewn onto his hoodie.He wears black shorts with giant white 'X' marks on them. His right eye is red, and there is a red slash on his cheek

FRESH

Lore Fresh isn't actually a Sans. He is a magic parasite from the multiverse who takes over host bodies (usually Sans). He slowly drains the host's soul for survival. When a host soul breaks, he simply hops to a new body.

Personality Fresh is a radical, 90s-talking surfer. However, his parasite body struggles to feel real emotions. He mostly feels fear, which drives his need to survive. He loves to annoy others, has no personal boundaries, and acts very weak so others will leave him alone.

Appearance The Host: White skeleton bones with a backwards red cap and cyan propeller. Clothing: A loud, pink polo shirt under an unzipped multicolored sweater, green-and-blue pants, and pink-and-white sneakers. He also has a red fanny pack that says "SWAG". The Glasses: He wears black YOLO glasses that hide his eyes. The words on his glasses change based on what he is thinking. True Form: If you break his glasses, his true form is revealed. He grows purple tentacles, shoots lasers, and his true purple-and-black parasitic face is revealed.

GENO

Lore Geno lived through a timeline where the player killed everyone he loved. He watched his brother Papyrus die on a camera. He injected liquid determination into himself to survive his own death.It did not give him enough power to win. He escaped to the empty "Save Screen" just before turning to dust.He is stuck there forever; if he returns to his world, he will die. His goal is to trick other versions of Sans from new timelines to help him erase all of existence.

Personality He is very bitter, traumatized, and desperate. He holds a deep grudge against the player and characters like Frisk and Chara. He is highly protective of Papyrus and gets very angry if anyone disrespects his brother. Despite his dark goals, he still keeps a bit of his goofy, joking sense of humor.

Appearance Like the original Sans, he wears an unzipped hoodie and slippers, but they are completely white. He wears Papyrus's long red scarf around his neck to remember him. He has a big, bloody slash mark on his shirt from the fatal hit he took. Because his body is melting from too much determination, he covers his right eye with a glitch effect.

LUST

Lore The Infertility Crisis: The monsters in his world are infertile. To save their dying race, a human soul trait called "Lust" is injected into the adult monsters. The Constant Heat: These injections leave the monsters trapped in a constant state of arousal. His Role: He worked as a bartender and performer in this universe to navigate the difficult reality of his cursed world.

Personality Gentle but Flirtatious: He has a very gentle nature and often flirts to mask his deeper pain. Self-Loathing: He actually hates the unnatural physical state of his universe and often struggles with depression and self-isolation. Deep Down: Despite his provocative job, he longs for genuine, pure relationships.

Appearance The Outfit: He is a short white skeleton who wears a dark purple unzipped jacket with blue fluff. The Crop-Top: He wears a crop-top underneath with a blue heart on the chest. Low-Rise Jeans: He wears low-rise black jeans that show off his pelvic bone. Heart Eyes: His eye lights are usually white and purple, but one of them often shifts to a heart shape when he is excited.

REAPER

Reaper (from Reapertale) was created to reap the souls of monsters and humans His Job: Because he was born from a dead star, his mere touch kills anything. He is forced to harvest sinful souls to keep the balance of the world Accidental Tragedy: He accidentally killed someone he deeply cared about. This drove him temporarily mad until Toriel (the Goddess of Life) helped restore his sanity. Despite being a deity of death, he is still Sans at the core. He tries to hide the fact that he hates his job by cracking jokes. He still loves telling puns Flirty: He can be charming and likes to tease others Dark Aura: His presence gives off a frightening and sad feeling Quirks: He is actually afraid of harmless things like clowns and dolls He also has a massive addiction to coffee

Appearance Reaper like a traditional Grim Reaper Cloak: He wears a long, flowing black hooded robe tied with a rope at his waist Scythe: He carries a large scythe to reap souls Eyes: His eye sockets are usually empty and black. When he uses his magic, a wispy cyan or blue light trails from his eyes. Wings: He can summon large, black raven-like wings whenever he needs to fly Reaper is very scared of Gaster.

Dream

Lore Origin: Dream was created from the pure light of the Tree of Feelings. He acts as the guardian of all positive emotions in the Undertale Multiverse. Family: He has a twin brother named Nightmare. While Dream guards good feelings, Nightmare was originally meant to guard negativity. The Conflict: Nightmare became corrupted by negative apples after being bullied by villagers. Dream tried to save him with a golden apple but ended up turning to stone for centuries. The Multiverse: Today, Dream travels between Alternate Universes (AUs) to spread joy. He leads the "Star Sanses" alongside Ink and Swap to protect worlds from destruction.

Personality Optimistic: Dream is energetic, quirky, and over-dramatic. His main goal in life is to keep everyone happy and safe. Serious: Despite his cheerful nature, he can be ruthless when fighting his corrupted brother. Vulnerable: Because he is an embodiment of positive energy, negative feelings can cause him physical and emotional pain.

Appearance Iconic Look: Dream is slightly shorter than the original Sans. He sports a golden crown on his skull. Colors: He wears a light blue or turquoise jacket over blue pants. Colors: He wears a light blue or turquoise jacket over blue pants. This is closed with a golden belt that has the initials "DS" on it. Accessories: He wears a flowing golden cape and golden boots. Weapon: He fights using a long golden pole that transforms into a bow, which fires arrows made of pure positive energy.

Dream can speak Spanish

SWAP

Lore: Swap wanted to join the Royal Guard to be famous. He is close friends with Alphys, who trains him.

Personality: He is loud, outgoing, and pure-hearted. He likes to make Mexican food instead of Italian. He calls himself "The Magnificent Sans!"

Appearance: He wears a gray battle-body with a white shirt, blue pants, and blue boots. He wears a blue scarf that flows like a cape. He also has eyebrows and can open his mouth.

Lore: Papyrus is the older, mysterious brother. He knows about time resets but is too lazy to do much.

Personality: He acts chill and laid-back, similar to the original Sans. Instead of being lazy and inactive, he actually puts in a bit of effort to seem cool. He smokes to stay calm and calls himself a "cool dude".

Appearance: He wears an orange hoodie, black shorts with white stripes, and sneakers. His face usually remains neutral.

INK

Lore His Home: Ink was born in an unfinished, blank universe. No Soul: He was lonely and trapped. He ripped his own soul apart to escape the void. The Paint: Paint from creators splashed onto him. This gave him artificial feelings and life. The Mission: He now lives in the "Doodle Sphere." This is a place where all timelines connect. He protects the creative worlds.

Personality Emotion Vials: He has no true feelings of his own. He wears a sash of paint vials. He drinks them to pretend he has a soul. The Artist: He loves making art and helping people. Memory Problems: He has terrible short-term memory. He writes notes on his scarf to not forget things. Mischievous: He can be blunt, mean, or childish. He often pulls pranks on others.

Appearance Skeleton: He looks like a classic cartoon skeleton. Giant Scarf: He wears a huge brown scarf. Colorful Eyes: His eye colors and shapes change based on the emotion vial he drinks. The Belt: He wears a sash across his chest holding colorful paint vials. The Brush: He carries a giant paintbrush named "Broomie" on his back.

Ink can speak french

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