Ordinarily, you're supposed to have 80 stars to finish the game, but with this glitch, you can finish it with 50. Go into the room on the third floor which contains the levels "Tick Tock Clock" and "Rainbow Ride". Once you enter this room (which requires 50 stars to enter), run to your right, and climb onto the second step. Angle your character so that they're about halfway between the corner and the edge (and have them facing the corner). When they're in this position, charge up a run, start running, slide kick, and hold right on the D-pad. If all goes well, you'll slide into the corner, and get shot into the sky. From here, you can navigate your way to the top of the endless stairs while they are still endless, and enter "Bowser in the Sky", and hence finish the game, with only 50 stars. This glitch can also be used to access "Bowser in the Sky" as characters other than Mario.