Things You'll Need
Instructions
Begin the game and collect 10 stars as fast as possible. The easiest way to do this is to collect the first star from each sub-world in the first floor, then get the remaining stars you need from Bob-Omb Battlefield.
Enter the door with the large star on it in the first floor and defeat Bowser in the sub-world behind the door. You will receive a key to the basement.
Get 20 stars as as fast as possible. The easiest way to do this is to get all the first two stars from the first floor and basement sub-worlds, then get the remaining stars from the first floor sub-worlds (this includes Big Boo's Haunt). You should have 30 stars when you are finished.
Enter the door with the large star on it in the basement, and defeat Bowser in the sub-world behind the door. You will then receive a key to the castle's upper levels.
Get 40 stars as fast as possible. The easiest way to do this is to get the first two stars from the remaining sub-worlds, then get the remaining stars from the basement worlds. You should have 70 stars when you are finished.
Enter the door with the large star on it in the castle's upper level. Defeat Bowser in the sub-world behind this door in order to beat the game.