Ultra Sans Is an AU in which Sans turns into a being more powerful than Asriel Dreemurr after being dealt a fatal blow. Ultra! Sans is a character in a Fan-Made AU with the same name made by A Huge Pancake. In the Genocide Route, Frisk/the player killed Sans. However, instead of dying, Sans transformed into a form a lot like Omega Flowey's, with a giant head, big arms and hands. It doesn't even have legs. Full info: https://undertale-au-fanon.fandom.com/wiki/Ultra_Sans