Use the following trick to defeat Bowser at end of story mode. Bowser starts by sending lots of fire-breathing Koopas after you. To defeat them, jump on their heads. However, make sure that they are not about to breathe fire or you will lose a heart point. This is followed by three fire rings that can expand, contract, or spin in any variety, and you must jump over them. After that, Bowser breaks out of the screen and begins to attack you by jumping on you, running into you, or breathing a lot of fire. You can avoid all those attacks by running around him in circles, but do not get too close or his spikes will hurt you. Notice the blocks that he jumps on will start to break; after he jumps on the same one three times, he falls through. Finally, he drinks a potion to make him huge. The red fireballs he throws out of his right paw can be picked up once they cool off. However, if you wait to pick them up after he starts to shoot fire, they will be reactivated and you can pick them up and throw them at him by pressing B button, by jumping and throwing on the little circle in front of the ledge near his nose. Do this five times, and you will succeed.