He wears a blue jacket/hoodie, white shirt, black shorts, and slippers, and is always grinning in the game. In his battle, he is seen with a distinct glowing left eye when using telekinesis, and fights with bones and gasterblasters as well. At one point during his battle, you're offered the option to spare him, which results in him killing you. In English, he exclaims "geeettttttt dunked on!!!", while in Japanese, he comments that all he did "was try to hug you...", prompting differences in fanart based on the region.
During the peak of the game's popularity, Sans gained memetic status due to his association with edgy and angsty teens on the internet, as well as numerous fan games involving him that were usually cheaply made and unfairly hard. His fan-made alternate universe versions would similarly be swept up in memes.
