As you are running up the stairs to fight Bowser for the final time, collect the 6 Life Mushroom and Life Shroom. You will first be on a sphere with spiky plants. Bowser will roll into a brick ball and chase you. When he is nearby, spin. Do this two times. Next, you will be at a rock with little plant things. He will breathe fire. Protect yourself by hiding behind the plant things. He will then curl up into his spiky shell and come at you fast. When he is close, hit the plant thing at him. Do this until you are at where you usually fight Bowser. Make him ground pound the glass and burn his tail. Hit him once, then hit him again when he is on his back. The last time you do this he will spin very fast. Time it, then hit him.