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 when he dodges X-Event!Chara's knife barrage, and slashes X-Event!Chara with one of them when he grabs one.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 sneak0ers. Often seen smoking, he is frequently depicted with a small toothy grin, dark circles under his eyes.