Bowsette.exe is an entity from a copy from New Super Mario Bros Deluxe. When Bowser wanted to find a way to defeat Mario and Co, he came up with the idea to experiment with the Super Crown. Only when he put it on then did the crown revealed to be possessed by an entity from a parallel world. It killed Bowser and transformed him from a male to an all-female, with the crown becoming inseparable from her, and now ruling a vast empire from other copies of the game.