After i get fifth star

Answer from: Luigi
If you mean "fifth course" and not "fifth star", then the fifth course is in the cage in the big boo in the castle backyard. Ground pound or punch the big boo to kill it and reveal the cage to Big Boo's Haunt. If you already got big boos haunt (course 5) and you've got 12 stars, you can go to the star door in the upper left part of the castle main hall. Run through the corridor there and you will fall into the first bowser course in the dark world. You need mario, luigi, or wario to beat bowser. get behind him, press A to grab his tail, circle the direction pad or the stylus and release A to throw him far far away. For this bowser level, if you throw bowser once into one of the spiked mines bombs, he is defeated, and gives you the key to the basement. Is this the answer you were looking for? i'm not sure. this is all i know. If you have 5 stars, just collect your 6th star and keep collecting stars and unlocking rooms, courses, and charcacters and secrets too.