Grrrr... I was hoping someone would ask how to get a 100 on Secret 5.... ah well...
Anyway, to beat Hookbill at the end of 4-8 (I think that is who you were refering to) you must first get a few eggs. Do this by jumping on his head, and he'll cough them up. Once you do that, hit him in the head about 4 times, which will cause him to gradually lose his balance, and if you did it correctly, Hookbill SHOULD end up on his back. Then, jump onto his stomach and do a Ground Pound (Jump + Down) and that is one hit. You must do this a total of 3 times to win.
If you EVER need help with ANY level of SMA3 or Yoshi's Island, I am the one to ask. I got 100s on every level of SMA3 3 days after I got it. I know my way around the game VERY well.
I don`t suffer from insanity. I enjoy every minute of it.