As a Sans but with the personality of Papyrus, US!Sans is kind, energetic and has a belief that everyone is a good person. This is broken after he's overwritten back to normal, and he fights X-Event!Chara even if Underswap!Chara is dying from it. He relies too much on his brother, so much that he wouldn't go without him, despite leaving Underswap when it was confirmed that he wouldn't come. When he's on his serious side, he'll spawn bones and Gaster Blasters at his will. He's also quick at dodging and grabbing attacks, as shown. Underswap!Sans consists of a gray shirt over-covered by a dark grayish one, dark pants, blue eyes, blue gloves, blue boots, and a scarf that comes out as a cape.

Underswap Papyrus is a laid-back, smoking, and comedic character who takes the role of Undertale's Sans. He is highly protective of his brother, Sans, and often shares a close, prank-filled friendship with Chara. While lazy and carefree, he can be serious when necessary, particularly in defending his friends. Underswap Papyrus is a tall, slender skeleton who takes on the role and laid-back personality of Undertale's Sans. He wears an orange hoodie, blue shorts, and sneakers. Often seen smoking, he is frequently depicted with a small toothy grin, dark circles under his eyes.

Species: Skeleton. Height: 3,8ft. Role: Creator of Au, and creator of Guest Funfact: Creator of Guest, along with Error sans, one day in a fight, tries to keep the fact Erro was apart of it out. Pupils: His eye pupils change their shape and color every time he blinks. Cheek Mark: He has a distinct black ink blot or mark on his right cheek. Body Markings: Underneath his clothes, his bones are covered in swirling dark markings and strange shapes. Scarf: He wears an oversized, tattered brown scarf that he often uses to scribble notes and reminders on. Shirt & Jacket: He wears a white long-sleeved undershirt with a small protector vest over it. Overalls: He wears brown overalls tucked into his waist, making them look like wide-legged pants. Belt & Vials: Work cross-belt across his chest holding rainbow-colored paint vials with heart-shaped tops, which he drinks from to maintain artificial emotions. Gloves: Wears light-green fingerless gloves resembling digital art tablet gloves. Footwear: Wears simple leggings instead of standard shoes. Broomie: carries a giant signature paintbrush strapped across his back, which he uses to bring his creations to life. Personality: deeply obsessed with creativity, inspiring creators, and filling empty or plain spaces with color. Suffers from a very short-term memory, often stopping mid-sentence to remember what he was just saying, which forces him to write important notes directly on his giant scarf. When he gets overly excited or energized, he has a strange habit of accidentally throwing up black ink or paint. loves playing pranks, acting wittily or provocatively, and sometimes teasing others or "being a jerk" just to make people laugh. He has an odd quirk of checking the height of every alternate-universe version of Sans because he is slightly shorter than the original Undertale Sans.

Error Sans is a glitchy, black skeleton, with mismatched eyes, and distinctive blue tear-like markings. Height: 5,3ft Species: Skeleton Role: Destroyer of Au, and creator of Guest. Head and FaceSkull: Completely black skull. Tear Marks: Bright blue, glowing streak-like markings run down from his eye sockets. Eyes: Mismatched and unsymmetrical. His right eye has a small white or red-bordered pupil, while his left eye is larger with a blue center, a thick yellow ring, and a black pupil. Sclera: Red background inside his eye sockets. Teeth and Fingers: A light yellowish color, often matching his finger tips. Glasses: Occasionally wears round red-framed glasses because his vision is damaged. Torso and Limbs: His upper body is mostly black, while his exposed lower legs are bright red. Jacket: A dark black coat or jacket featuring a blue hood which transition from dark to bright blue with blue stitching or accents. Pants: Black sweatpants decorated with vertical blue stripes down each leg. Footwear: Dark red slippers. Glitch Effect: The word "ERROR" often floats or glitches around his body alongside blue magic strings. Personality: deadset on destroying alternate universes (AUs) and feels justified doing it, acting as a self-appointed "cleanser" of timelines. His mental state is unstable, causing him to swing rapidly from calm to extreme rage. Despite knowing he is an anomaly and a glitch himself, he hypocritically targets other versions of characters as bugs that must be deleted. He intensely dislikes being touched and will glitch out, crash, or panic if someone makes physical contact with him. Spends time in the quiet Anti-Void making and talking to puppet versions of his alternative selves, numbering them or calling Classic Sans "Sans Classic". Loves chocolate, quiet blank spaces, and sleeping, strongly hate loud noises, clutter, physical contact, and Ink! Sans. Funfact: Guest is one being he doesn't see as a glitch or anomaly, since they were created with apart of him after a fight with Ink. Meeting Guest in secret and grown fond of the kid. Potentially taking Guest is another way to get back at Ink sans.