Error Sans

He was born from Geno Sans, who escaped the save screen in Aftertale and became trapped in the Anti-Void. Alone, Geno went insane, his code glitched, and he became the destroyer of alternate universes (AUs), considering them "errors."

Error's skeleton is black; his bones are black. His teeth, however, are yellowish.
Eyes and "Tears": His eye sockets are red. His right eye is small and yellow, while his left eye is larger, surrounded by a blue circle and a yellow pupil. He has permanent blue "tear marks" that run down from his eyes.

Clothing: Coat: He wears a black coat with blue details (especially on the hood and hem).
Blouse: Underneath, she wears a red t-shirt.
Pants: He wears black shorts with blue stripes.
Feet: He wears black slippers.
Glitches: His body is constantly surrounded by error signals (squares with the word "ERROR" or pixelated code blocks) that float around him.
Glasses: Error has terrible eyesight. He owns a pair of red prescription glasses that he occasionally wears for reading or knitting (although he's embarrassed to wear them in public).

Unstable, psychotic, and erratic: He is mentally unstable because of the glitches. His mood changes rapidly—he can go from calm (or "grumpy") to furious or manic in seconds. He hears voices, has seizures, and is unpredictable.
Destructive and hypocritical "missionary": Error sees himself as the "cleaner" of the multiverse, destroying AUs that he considers "glitches" or anomalies to leave only "the original." He thinks he's helping, but he's a hypocrite because he himself is a glitch/anomaly. He destroys timelines randomly without a clear plan.
Grumpy, sarcastic, and playful: He tends to be grumpy, snarky (makes sarcastic comments), and likes to tease his enemies. He has a playful side—he loves jokes, teasing, and stealing things. Sometimes he acts like a "manchild" (spoiled overgrown child) who throws tantrums when things don't go his way.
Lonely and traumatized: He has haphephobia (extreme fear of being touched), which makes him avoid physical contact (he recoils or reacts badly). He lives isolated in the Anti-Void, which has made him even more insane and lonely. He makes "puppets" of other Sans to talk to, showing his need for companionship, but he treats everything in a distorted way.
Other details: Selfish, jealous/protective of what he considers "his," likes chocolate, and has a particular hatred for non-canon creations that deviate too much from the original Undertale. He can be tsundere or even affectionate with those he considers "his."