majorgamer

You have to get the key first. You can find it when you enter the door that led you to the boo's haunted mansion. But
Instead turn to your left and you will come to some stairs the opposite direction of the boo's place and when you
Get to the bottom of the stairs enter the door and turn to your left than enter that door with th big star and jump into the blue water wall. You'll figure out what to do next when you enter.






Hope this helps! From Majorgamer.