The .zip file comes with different versions of the game. Choose the one you'll like best:

-In Bowsette Edition A, the events of the original game are repeated, only with Bowser having-a-monster-girl-like body instead of his regular turtle-dragon-monster self.

-In Bowsette Edition B, Princess Peach has succumbed to madness and has captured Bowsette AND taken over Bowser's Koopa Troop during his/her visit to Dinosaur Land.

Credits:

Moltz
FuSoYa
Sonikku
Alcaro
Tsutarja
Smallhacker
JackTheSpades