Dust sans

In the original progression of Undertale, the player's interactions with the underground dictates how Sans behaves. This means that he changes depending on the "route" that a player runs: Neutral, True Pacifist or Genocide.

This story line follows the possibility of the player abusing their ability to reset the timeline to repeat the Genocide Route as many times as they want.

Sans the only character that shows awareness of the player's ability to reset time and revive themselves after death. In this take, it is that same acute sensibility that causes Sans to realize the underground has been reset and slaughtered repeatedly.

His response to this realization is to beat the player to the punch; he slaughters the entire underground himself, including his brother Papyrus, with the intent to gain enough power to stop the player from completing another Genocide Route.

This series of actions drives Sans to madness, causing him to hallucinate the specter of his deceased brother.

Murder!Sans's appearance slightly deviates from the original design. He wears a blue hoodie with a grey hood, of which he keeps up, black shorts with white lining and a pair of gray slippers. His bad time eye is the only thing that truly differs, having changed color from a blue and yellow to a blue surrounded by red and even having a second red magic eye. He is usually depicted as having grey dust coating his clothing.

After the human reset and did numerous Genocide Routes, one day due to unknown circumstances Sans suddenly remembered all the Genocide Routes. This changed Sans, and made him kill other monsters for LV; even going as far as killing his own brother. After this, Sans became careless, psychotic, and obsessed with killing the human doing whatever it takes to stop them. Despite being extremely careless, Sans does seem to regret killing Papyrus. Murder!Sans is typically depicted as a deranged, unstable character with symptoms of severe schizophrenia. He displays little emotion besides that of desire to kill the player and seems willing to do anything to accomplish that goal. Additionally, he has an active auditory and visual hallucination of his dead brother Papyrus, of whom encourages Sans to keep down the same path he started on.

Powers:

Gaster Blasters: Devices resembling a skull that shoot large beams; the amount of damage inflicted from these beams depends on how much LV Sans has.

Bone Manipulation: Sans has the ability to summon control and manipulate bones at will.

Soul Manipulation: Blue Mode: Sans can can make enemy souls affected by gravity While affected by blue mode, enemies have their movement heavily restricted, and are only able to jump to move.

Blue Attacks: Sans can do attacks that do not deal damage as long as the target remains still.

Shortcuts: Sans can travel or teleport anywhere instantly.

Aim Dodging: Sans can dodge linear attacks.

Body Making: Sans can create any body part in his body by using his blue magic. He can create a blue tongue, or a blue penis if he wishes to.

KR: A kind of "poison" effect of Sans's attacks, getting hit inflicts not just the initial damage received, but also increases KARMA by some amount (depending on the attack). Whenever KARMA is above zero, it eventually drains back down to zero, inflicting damage with each drain.

Relationships:

Papyrus: Papyrus is Sans's younger brother whom he slaughters in the hopes of gaining more power to defeat the player. The killing of his brother was a great breaking point of his sanity, and after that began to have a constant hallucination of Papyrus who frequently goads him to achieve his violent goals.

The human/player: They are Sans's driving force for gaining LV, and he aims to put an end to them permanently.

According to the creator, Sans drinks.

Sans's eyes are usually white, but when in combat or having trouble controlling his emotions turns red and blue, especially when he is angry or unstable. When he is sad or depressed, his eyes will be white.

Sans doesn't wear Papyrus’s cape.

Sans only uses his magic and can't use other Monster's magic, he can replicate them using bone attacks but there's no reason for him to do so.

He wears gray slippers, but it doesn't matter what footwear you draw him in.

He changes his attack patterns each time the human returns.

His soul remains the same.

He knows about save points, but is unable to see them.

Sans doesn't use purple bones.

He wears his hood to keep dust out of his face, and to not show himself to others.

Sans is aware Phantom!Papyrus isn't real.

Sans can remember resets.

He wears the same clothes as his Undertale counterpart.

Sans is rationally insane.

He HATES humans or anyone who enters the Underground from the Surface. He’s very aggressive towards them and would personally see through it by getting rid of them permanently.