Beating this level will lead you to the Star Road. At the beginning of the level, dodge the falling pillars and the spiky wheels. Spin jump them if necessary; that will not hurt Mario. Having hit the colored switches will help you greatly in this level. You will fight the Reznors at the end of this level.
Near the end of the level, when you see the first big red door, jump up to the grey ledge and proceed to the right. It is extremely tricky, but if you can demonstrate top-notch flying skills by flying over the long lava pit to the right, you'll earn nine 1-ups!
If you touch the jumping flames, you'll fall in the lava and lose a life. The key to getting over the pit without hitting the jumping flames is to keep Mario as close to the ceiling as possible. Press the back key as soon as Mario's head dips downward to boost him up again. An alternate method is to use a flying spin and then while spinning bounce from fireball to fireball. You might need to experiment a little to get the timing just right. It's tricky, but you'll be rewarded!