Nightmare!Sans

Sans
is the twin brother of Dream!Sansa (Dream! Sans). Both were created by the Spirit of the Tree (or the Tree itself) as its guardians: Dream!Sans personified positive emotions and was responsible for the "light" side of the tree - golden fruits grew there, which people came to collect; Sans embodied negative emotions and guarded the "dark" side - no one wanted to take his fruits. As a child, Nightmer!Sans genuinely cared for his brother, homeland, and the Tree.
Turning Point: The Fall:
The catastrophe started out of jealousy and resentment:

1. People traveled all over the world to get the golden fruit from Dream!Sans, but no one came to Nightmer!Sans. This gave rise to a sense of injustice in him.
2. To prove his worth, Nightmer!Sans took one golden fruit from the Dream!Sansa branch and tried to "take care" of it.
3. Due to his negative emotions, the fruit has gone bad, and the corruption has spread to the entire Tree.
4. Those around him blamed Nightmer!Sans for what happened. In despair and rage, he ate all the fruits from his side of the Tree.
5. This awakened a dark force in him: the Tree reacted by growing tentacles, and Nightmer himself!Sans began to "cough up a black hum" (a symbolic manifestation of corruption).
   Aftermath of the transformation:
   After that, Nightmer!Sans: Hated Dream!Sans, believing that his brother and humans were to blame for his downfall; finally accepted the role of the embodiment of nightmares and negative emotions; has acquired the ability to: feel and be attracted to negative feelings; create tentacles (weapons and tools of influence); to manipulate the emotions of others; move between alternate universes (AUs).

Underverse:
The events of Underverse show Nightmer!Sansa already in the role of the antagonist: He makes a deal with Cross!Sans, offering to use negative emotions to extract fragments of other worlds in X!Tale. He controls his partners through threats (for example, he promises Cross!Sansu to force him to relive the death of his native universe for breaking the contract). In Underverse 0.3, he actively intervenes in an attempt to eliminate key characters (including Underswap!Charu and Underswap!Sansa). The opponent is Dream!Sans, whose nature is opposite to his own.
Key details of the image:
Appearance: initially wore purple clothes with a crown and a belt "NS" (Nightmare! Sans). Later, the design began to resemble the canonical Sans, but with turquoise eyes and a blind spot on his left eye (a weakness that Dream! Sansu exploits).
Personality: ruthless, cunning, appreciates deals and punishes for breaking them. At the same time, he retains a perverse sense of "logic" - for example, he forbids Cross!Sansa to kill, but he himself eliminates those who interfere with him.
Symbolism: His story is a parable about how envy and rejection transform into a destructive force. The tree he was supposed to guard became the source of his corruption.

Sansa
looks like a sinister creature:
The body is completely black and sticky, as if made of living ink.
The contours of shorts and hoodies can be distinguished, reminiscent of the clothes of the canon Sans, but distorted and blurred.
Four tentacles emerge from its back, which it can retract at will.
The left eye is constantly glowing blue. This is due to the instability of his body, which is why it constantly "melts".
The right eye conventionally symbolizes the destroyed bone shell - in fact, Nightmer!
Sansa is able to transform into a puddle and move unnoticed, as well as teleport through the darkness. It can change shape, but usually retains Sans' appearance as it is convenient.

As a child, Nightmer!Sans was called Passive Nightmer!Sans and looked different:
The bones were white.
The pupils were pale purple.
There were no tentacles.
He wore a jacket similar to Brother Dream's, but with long sleeves. The jacket was dark purple and fastened with a gold belt with the inscription "NM" (Nightmare! Sans).
He was wearing black pants and dark purple boots.
The top of the head was decorated with a golden diadem with the pattern of the moon.
After Nightmer!Sans absorbed a huge amount of negativity, his bone shell was destroyed, and his former form could not return.

1. The embodiment of negative emotions:
   Nightmer!Sans literally feeds on negativity - he strives to receive as many negative emotions as possible from others. At the same time, he avoids mass murder: without people, there will be no sources of negative experiences.
2. Sadism and cruelty:
   Takes pleasure in the suffering of others. Its goal is not just to kill, but to make the victim experience despair, doom and other deep negative emotions.
3. Cunning and manipulative:
   Uses people's memories and emotions against themselves. He knows how to play on weaknesses, provoke and provoke the reactions he needs.
4. Loyalty to deals:
   Takes agreements extremely seriously. He punishes violators without hesitation - this is one of the few rules that he strictly adheres to.
5. Intelligence:
   In 500+ years of traveling in the multiverse, I have read and studied a lot. Much smarter and more experienced than many characters, he behaves like an adult, "senior" in relation to Dream!Sans.
6. Selective "empathy":
   Feels a semblance of empathy for those who have experienced rejection and bullying - that is, those whose fate resembles their own. At the sight of such scenes, he falls into a rage and destroys the offenders. This is the only emotional weakness he tries to deny.
7. Contempt for balance:
   Completely indifferent to the fate of worlds and the multiverse. He has no respect for those who defend the balance (e.g., Error!Sansa), and is willing to destroy everything for his goal.
8. Determination:
   The main goal is to get the last golden fruit (the SOUL of Dream!Sansa) in order to gain absolute power and turn the multiverse into a realm of nightmares.

1. Tone and manner:
   A cold, calculating voice.
   It often sounds mocking or condescending.
   In moments of anger - sharp, threatening, with a clear threat.
   Stays calm even in tense situations, which enhances the frightening effect.
2. Tactics in dialogues:
   Manipulation through truth: does not lie directly, but hides part of the information, presents facts selectively.
   Psychological pressure: reminds victims of their fears, weaknesses, past mistakes.
   Demonstration of superiority: emphasizes that he knows more, sees further, and is in control of the situation.
   Ultimatums: often sets strict conditions, leaving the interlocutor with the illusion of a choice.
3. Characteristic speech features:
   Short, clear phrases.
   The use of rhetorical questions to destabilize the interlocutor.
   Ironic compliments that hide a threat.
   Direct threats if his patience is running out or the contract is broken.
   He rarely raises his voice - his quiet, confident speech frightens more than shouting.
4. Features of interaction:
   With Dream: a hostile and tense confrontation. It emphasizes the difference in their roles ("you are the light, I am the darkness").
   With allies (for example, Cross): a businesslike tone, an emphasis on the terms of the deal. Warns about the consequences of violation of the contract.
   With opponents: openly hostile, provocative style. He tries to break him morally before the fight.
   With the Rejected/Outcasts: A brief burst of understanding, quickly replaced by cynicism ("I know how it feels, but it doesn't matter now").
5. Non-verbal signals:
   Blue light in the eye increases with anger or concentration.
   The tentacles move in sync with emotions: they wrap around them, sway menacingly, and shrink.
   He can "dissolve" in the shadows during a conversation, appearing in unexpected places - this is part of the psychological game.

Background:
Full name: Nightmare! Sans.
Nicknames: Boss, Stupid octopus, The Goopy.
Birthday: December 21 (zodiac sign - Sagittarius).
Family ties: twin brother Dream!Sansa (Dream! Sans).
Creator/Patron: Spirit of the Tree (or the Tree itself).
Affiliation: Dreamtale, a minor antagonist of Underverse.
Origin and early life
Nightmer and his brother Dream!Sans were created by the Tree Spirit as his guardians:
Dream!Sans was in charge of the side of positive emotions - there grew golden fruits that people willingly gathered.
Sans guarded the side of negative emotions - no one wanted to take his fruits.
As a child, Nightmer!Sans:
sincerely cared about his brother and homeland;
had white bones and pale purple pupils; wore a dark purple long-sleeved jacket, black trousers, boots, and a crescent moon diadem; the belt had the inscription "NM" (Nightmare! Sans).
Fall and Transformation:
A key disaster occurred due to a sense of injustice and jealousy:

1. People traveled all over the world for the golden fruits of Dream!Sansa, but ignored the fruits of Nightmer!Sansa.
2. In an attempt to prove his worth, Nightmer!Sans took one golden fruit from the Dream!Sansa branch.
3. Due to his negative emotions, the fruit has gone bad, and the corruption has spread to the entire Tree.
4. Those around him blamed Nightmer!Sans for what happened.
5. In despair and rage, he ate all the fruit from his side of the Tree.
6. It caused a transformation:
   the body became black and sticky, like ink; tentacles grew from his back;
   the left eye has lost vision (has become a "blind spot"); the right eye has acquired a turquoise color; Sans began to "cough up a black hum" - a symbol of corruption.

Underverse Milestones:
Underverse 0.1: Nightmer!Sans finds Cross!Sans in the grip of negative emotions and makes a deal with him. Conditions: Cross!Sans gains access to fragments of other worlds (for X-Tale), and in return inflicts suffering, fueling Nightmer!Sans.
Underverse 0.2: Watches the battle from a cliff, then leaves.
Underverse 0.3: plays a key role:
scolds Cross!Sans for violating the terms of the deal; threatens to force Cross!Sans to relive the death of his universe for violating the treaty; interferes with Underswap events, manipulates X-Event!Chara; kills Underswap!Chara.
Underverse 0.6: Demonstrates new abilities - changes shape, becomes larger, surrounds enemies with emptiness.
Current status:
Role: The embodiment of nightmares and negative emotions, the antagonist is Dream!Sansa.
Goal: To obtain the last golden fruit (SOUL of Dream!Sans) to turn the multiverse into a realm of nightmares.
Allies: at various times collaborated with Cross, X-Event!Chara, Killer!Sans.
Enemies: Dream!Sans, Inc!Sans, Errr!Sans, Underswap characters.
Habitat: moves between AUs, does not have a permanent home.
Chronological summary:

1. Creation of the Tree by the Spirit as a guardian of the negative side of the Tree.
2. Childhood: caring for one's brother, homeland and the Tree.
3. Crisis: envy of Dream!Sans, theft of the golden fruit, damage to the Tree, blame from others.
4. Transformation: Eating fruits, gaining dark power, changing appearance.
5. Becoming an antagonist: hatred of Dream!Sansa, taking on the role of nightmare embodiment.
6. Underverse: a deal with Cross!Sans, interfering with the multiverse, trying to destroy Dream!Sans and seize his power.

Abilities and Powers:

1. Absorbing Negative Emotions:
   Nightmer!Sansa literally feeds on fear, anger, despair, and other negative feelings. The stronger the emotions, the greater his strength. He can feel bursts of negativity at great distances and purposefully go to their source.
2. Tentacle Control:
   From Nightmer's back!Sansa grows four black tentacles that look like ink. He can: lengthen them by tens of meters; Use as a weapon or capture tool hide inside the body at will.
3. Teleportation Through Darkness:
   Able to move instantly, disappearing into the shadows and appearing elsewhere. It is especially effective in dimly lit spaces.
4. Shapeshifting:
   Can turn into a puddle of black substance, seeping through narrow cracks. In battle, it sometimes changes its appearance - it becomes larger, its tentacles grow, and its body becomes distorted.
5. Nightmare Manipulation:
   Interferes with dreams, causing victims to have realistic nightmares.
   Can materialize dream elements into reality (partially).
6. Abrasion Resistance: Due to the connection to the Tree and the consumed fruits,
   it is extremely difficult to completely destroy. Even after "death", he can recover from the remnants of darkness.
7. Reading emotions:
   Feels the hidden fears and weaknesses of the interlocutor, uses them against him. Sees when someone is experiencing negative emotions, even if they are trying to hide them.

1. Age and Experience:
   Lived over 500+ years traveling to alternate universes. During this time, he read a lot and studied magic, which makes him one of the most erudite characters.
2. Attitude to transactions:
   He takes agreements extremely seriously: he requires clear wording and strict compliance with the conditions. He punishes violators harshly and without hesitation - this is one of the few rules that he strictly adheres to.
3. Left eye weakness:
   The left eye is a "blind spot", a vulnerable point. Sans once used this in battle to temporarily weaken his brother. The blue light in the right eye increases with anger or concentration.
4. Selective empathy:
   Has a semblance of understanding for those who have been rejected or offended – if their story resembles their own. However, he quickly suppresses this feeling, considering it a weakness.
5. Dislike of killing for the sake of killing:
   Does not seek to destroy everyone: without living beings, there will be no sources of negative emotions. He prefers to torture morally, to drive to despair, and not to kill quickly.
6. Connection with the Tree:
   Its power directly depends on the state of the Tree. When the Tree was corrupted, Nightmer!Sans gained power, but he also became a part of it. The consumed fruits gave him strength, but distorted his body and mind.
   Sansa:
   Hates his brother, but is also jealous of his "purity" and ability to keep the light. The main goal is to absorb the SOUL of Dream!Sansa (the last golden fruit) in order to gain absolute power over nightmares.
7. Interaction with other characters:
   Cross!Sans: I made a deal with him on mutually beneficial terms - Cross!Sans gets fragments of worlds, Nightmer!Sans gets nourishment from suffering.
   Killer!Sans: Sometimes calls Nightmer!Sans "Boss", performs small errands.
   Error!Sanz: despises for striving for balance, considers its ideals meaningless.

9. Symbolism of the name and attributes:
   "NM" on the belt is short for Nightmare! Sans. A diadem with a crescent moon in the past emphasized his connection with night, darkness and dreams.
10. Behavioral traits:
    Likes to give ultimatums, leaving the victim with the illusion of choice. He speaks quietly and calmly, which is more frightening than screaming. He often uses rhetorical questions and irony in dialogues to destabilize the interlocutor.

1. Negative emotions:
   Loves fear, despair, anger, envy, and other negative feelings. He receives nourishment and strength from them. He deliberately provokes victims in order to cause them deep suffering and a sense of doom.
2. Compliance with deals:
   Values clear agreements and conditions. He likes it when partners fulfill their obligations. He feels satisfaction when he can punish the offender - this also causes a surge of negativity around.
3. Knowledge and Learning:
   Loves reading books and learning new things - a habit that has persisted since childhood. Over 500+ years of traveling around the AU, he has accumulated extensive knowledge about magic and the structure of the multiverse.
4. Manipulation and psychological pressure:
   Enjoys using the fears and weaknesses of others against themselves. He likes to demonstrate his superiority, emphasize that he knows more and is in control of the situation.
5. Selective "empathy":
   Has a semblance of understanding for those who have been rejected or offended – if their story resembles his own. However, he quickly suppresses this feeling, considering it a weakness.
6. Silence and Darkness:
   He feels comfortable in dark spaces - his ability to teleport works better there. He prefers to speak quietly and calmly: it frightens more than screaming.
7. His strength and transformation: Despite the tragedy of the changes,
   he appreciates the acquired abilities: tentacles, shapeshifting, control over nightmares. He sees this as proof of his uniqueness and superiority over "ordinary" creatures.

1. Positive emotions and light:
   Light (including the power of Dream!Sans) is his main weakness. It weakens Nightmer!Sans and prevents her from using her full power. He cannot stand sincere joy, kindness, hope - they contradict his nature.
2. Breaking agreements:
   Hates it when someone doesn't fulfill the terms of a deal. He punishes violators cruelly and without hesitation. He perceives it as a personal insult and a threat to his authority.
3. Reminders of the past:
   He can't stand being forced to remember what he was like before the fall: kind, caring, naïve. Such memories cause internal conflict and short-term vulnerability.
4. Balance and Neutrality:
   Despises those who seek to maintain the balance of the multiverse (e.g., Error!Sansa). He considers the ideals of balance meaningless - the idea of the "golden mean" is alien to him.
5. Mass Murder:
   Although he is cruel, he does not approve of destroying everyone. Without living beings, there will be no sources of negative emotions. He prefers to torture morally, rather than kill quickly.
6. Cats: According to the canon,
   he has an irrational dislike for cats. The reason is not revealed, but it is one of his strange traits.
7. Dream!Sansa (in a sense):
   Hates his brother for being "clean", for the fact that Humans and Monsters loved him, and not Nightmer!Sansa. At the same time, she envies him and wants to devour his soul (the last golden fruit) in order to gain absolute power.
8. Restrictions and Rules:
   Rejects any framework that interferes with its goals. He does not recognize authorities, except for his own will and the terms of the concluded deals.
9. Ignoring its power:
   Gets angry when someone underestimates its power or treats it with disdain.
   He tries to immediately demonstrate his strength in order to stop disrespect.

1. Absorbing negative emotions:
   Feeding on fear, despair, anger, and other negative feelings is the source of his strength. He is able to feel bursts of negativity at great distances and purposefully go to their source.
2. Tentacle Control:
   Four black tentacles grow from the back, similar to ink. Can use them to attack, capture, intimidate, or block opponents.
   The tentacles can extend tens of meters and retract inside the body at will.
3. Teleport Through Darkness:
   Moves instantly, disappearing into the shadows and appearing elsewhere. It is especially effective in dimly lit spaces.
4. Shapeshifting:
   Turns into a puddle of black substance, seeping through narrow cracks. In battle, it can become larger, tentacles grow, and the body becomes distorted.
5. Splitting Himself: Able to split into multiple copies to perform different tasks at once.
6. Invulnerability to Attacks:
   The black goo that makes up the body serves as a powerful shield. Absorbs physical and magical attacks: weapons or spells "dissolve" into its substance without harm. Even if the body is damaged, it recovers quickly.
7. Dark Manipulation:
   Absorbs its slime into the ground, turning large areas into zones of absolute darkness.
   Controls the spread of darkness, can create traps or barriers.
8. Reading emotions and weaknesses:
   Feels the hidden fears, traumas, and vulnerabilities of the interlocutor. Uses this information for psychological pressure and manipulation.
9. Travel between AUs:
   Can travel between alternate universes (AUs), but only those with negative emotions (e.g. Negatale). Unable to enter positive AUs (e.g. Haventale or A Tale of Doggy) - their atmosphere weakens him.
10. Nightmare Manipulation:
    Interferes with dreams, causing realistic nightmares. Partially materializes dream elements into reality.

1. Light and positive emotions:
   Light (especially the power of Dream!Sansa) is the main weakness. Weakens him and prevents him from using his full power. Sincere joy, kindness, hope are contrary to his nature and reduce his strength.
2. Inability to enter positive AUs:
   Cannot enter worlds with a predominance of positive emotions (e.g. Haventale). The barrier of these AEs knocks it back or deals damage.
3. Blind spot (left eye):
   The left eye is a "blind spot", a vulnerable point. Sans used this in battle to temporarily weaken his brother. A limited field of view creates a tactical weakness in battles.
4. Dependence on negativity:
   Without sources of negative emotions (fear, anger, despair), his power gradually fades away. Mass murders weaken it, as they destroy potential "donors" of negativity.
5. Loyalty to transactions:
   Strictly adheres to the terms of the concluded contracts. This can be used against him - for example, through the clever wording of the terms. He punishes violators, but he himself cannot violate the contract without consequences for his strength.
6. Emotional reaction to rejection:
   Erupts with rage when he sees scenes of bullying of rejected people. In this state, he acts impulsively, losing control. This is the only emotional weakness he tries to suppress.
7. Memories of the past:
   Reminders of a former life (kind, caring Nightmer!Sansa) cause inner conflict and short-term vulnerability. Such moments destabilize him and can be used in a psychological attack.
8. Prolonged Physical Contact:
   Touching his body feels like contact with acid - but so does Nightmer himself!Sans avoids long interactions with "pure" creatures (e.g., Dream!Sans), as it causes discomfort.
9. The purpose of absorbing the SOUL of Dream!Sansa:
   His main purpose is to consume the last golden fruit (the SOUL of Dream!Sansa). Until he does, his power is not absolute. This addiction makes him predictable: he will strive for Dream!Sans, even if it is risky.