I heard from people at Newgrounds.com that they are having trouble with the final bowser battle (and the meteor).
So I decided to post a guide here for anyone else that needs help, (oh and mods. Please sticky this if you can, it will help people in the future.) Now lets start the walkthrough,
~THE FINAL BOSS~
We start out with bowser standing on the opposite side of the battle platform. Wait until he jumps up and shoots fire balls, Then run under him. You will now be behind bowser, (this part is hard to explain but ill try to tell you as best as I can)
Quickly jump up facing bowser and press down. Mario will dive at bowser`s tail and will grab it, You will go spinning in the air with bowser. Press SPACE at the right time to send bowser flying at one of the spikey-orbs, He will get damaged. (About 90% of the time he falls off the platform after he gets hit so be patient for him to jump back up to the platform.)
After three hits he will fall off and die. Congragulations, you killed bowser. But you aren`t done yet,
WARNING! SPOILERS!
Peach comes out of her cage and thanks mario. But before they can do anything else, the ground shakes. Kamek comes and puts a reverse spell on the meteor controller to destroy bowser`s castle, But then a meteor falls where mario is standing and the castle crumbles apart. Leaving mario falling.
~THE FINAL LEVEL~
The final challenge has begun, Jump on platforms and try not to hit the lava. Keep running and jumping until you see a spinning platform spinning slowy, This part is hard so don`t get mad at me if you fail. When it is the right time, Jump on the platform and continue until you reach the second part. You are now in the castle grounds, Keep jumping over lava and get blue coins when they are available. Then you will see several pieces of the castle spinnning in air, Jump on them and try not to fall. Then jump at the right time to get to the next platform. Yet continue until you reach the third part, When you get to the third part, most of the castle is destroyed and it looks like the meteor is floating above the lava. There is not much to explain at this part but to jump off of sinking platforms,
After you beat the third part and hop in the sling star a short cutscene will play where the meteor destroys what remains of bowser`s castle. Awesome! you beat Super mario 63! now grab some popcorn and watch the cool ending credits.