Popcornpr1nce is the creator of Underswap.
The AU was always meant to switch not only the roles, but the personalities of almost every main character, along with occasionally switching interests for some characters, such as changing Sans' iconic food to Tacos instead of Spaghetti, along with changing the laugh to "MWEH HEH HEH", but popcornpr1nce's personal blog still states that Sans is a skeleton who would make puns.
Though, in many interpretations of Underswap, people didn't apply the part about Sans still liking puns and many treat Sans as if he hated them. Many end up going for a full personality swap in that regard.
Since then, Popcornpr1nce has abandoned the idea and concept of Underswap due to not liking how the fans have treated it, due to turning Sans' behavior in many common interpretations into the likes of a child, and giving him the name "Blueberry", and Papyrus the name "Carrot".