Will give

Wears a dark hoodie and scarf, creating a secretive, "closed" look
The eyes glow red, sometimes with a glitch effect - a hint of instability
Often depicted with a cigarette, a detail that emphasizes fatigue and indifference.
His appearance is more "dirty" and worn out than the normal Sans.
The color palette is cold: blue, gray and black shades.

Character
Cold, distant and emotionally repressed
Has lost trust in others and shows little empathy
Inside there is a strong fatigue and emptiness
Acts decisively and without hesitation if he considers it necessary
Doesn't like unnecessary conversations - prefers silence.

Main features
Cold and distant - hardly shows emotions, keeps his distance
Psychologically broken - has been through too much, which has made him tough
Indifferent - rarely shows empathy, seems "empty" inside
Silent - doesn't like to talk without reason
⚔️ In behavior
Cruel when necessary - does not hesitate when it comes to violence
Decisive - acts quickly and without unnecessary doubts
Distrustful - trusts almost no one
🕳️ Internal state
Constant fatigue and a feeling of meaninglessness
Suppressed emotions that he doesn't show
Somewhere deep down there may still be an “old Sans,” but it’s almost completely hidden.

Behavior and essence
This is a version of Sans broken by repeated events (in an AU story)
He became more aggressive and dangerous.
It may look calm, but it is more of a "cold void" than control.
Often keeps aloof from others