As either Super or Fiery Mario, get behind Bowser and let him walk towards you. Jump, and try to land on the axe and Bowser at the same time. You will defeat Bowser and move on as Super Mario. In the next World, the next power-up you'll get is a Mushroom, which will make Mario small! The next power-up will be a Fire Flower, which will turn you Fiery, but you will remain small. Note: This will not work in 8-4.