More on the story in Flowerfell.
Flowerfell Sans looks a lot like Underfell Sans, with the gray jacket, spiked teeth, single gold tooth, and red T-shirt, but there are some differences. He is constantly wearing a black scarf with red stripes and a necklace which looks like a SAVE point. He also has a single red eye. Sometimes he is depicted without his jacket.
Sans is shown to be evil, awful, and murderous once Frisk reached Snowdin, but after Frisk lost their sight, Sans' personality changes to kind and helpful throughout the way. He also acts as a guide for Frisk.