In some Neutral Endings, Sans is afraid to tell Papyrus about other characters' deaths, so he lies about them going on a vacation. Sans worries about others hurting Papyrus or taking advantage of him. He also leaves a dirty sock in their living room for Papyrus to fuss over. He likes to mess with Papyrus, as he sends him 'bad puns in a goofy font' on the UnderNet. He deeply cares for and admires his brother, Papyrus, and reads him bedtime stories. He is kind and reassuring, but becomes eerily serious at abrupt moments (particularly when angry). He enjoys making bad puns, usually relating to skeletons, to the annoyance of his brother. He does just enough work to avoid being fired by Undyne. Sans is shown to be very laid-back and flippant, sleeping on the job as often as he takes breaks. This eye starts off merely glowing, but as he utilizes his time warping powers, it starts to flash vividly.

A bright, flashing iris appears in his left eye during the battle against him, as well. He has white pupils, which tend to disappear when he is serious. He is seen with a very large toothy grin at all times, and hardly moves the corners of his mouth. One strange thing about his skeletal body are his hands which look more like mittens rather than skeletal hands. He has a huge round skull shaped similarly to a slice of bread and has large bags under his eye sockets, which have white glowing pupils floating in it. Sans is an extremely short and big-boned skeleton, wearing a light-blue hoodie, unzipped at all times, with a white tank-top underneath, black shorts and salmon slippers according to his official Fangamer plushie and Super Smash Bros.

Boss monster undertale sans