From the Super Mario Wiki
Garamond is a best-selling novelist living on Flopside's first floor who Mario meets during Super Paper Mario. He writes very quickly and is incredibly successful, and is named for the Garamond font. He receives his inspiration from a man in his dreams, who Mario later discovers to be Helvetica, a Flipsider. When Merlon learns of Helvetica purposefully sending Garamond ideas through his dreams, he suggests the two should swap places. Then, after the player beats the game, they will find that Garamond will have indeed switched with Helvetica, and lives in Helvetica's house in Flipside from then on.