After star dust fields go to the place where the man and the women are standing on a bridge talking about their pores go to the end on the right hand side there is a little gush of water put mario in frount of it press
up and walk into it mario should become really fat walk downwards then turn left not along the bridge at the end there should be a turbine get luigi to jump on marios head while facing the turbine then a mushroom or a coin will pop out go back fill mario up and repeat until you get unlimit stuff.