my little 7 year old brothers figured this out, and i've been playing this game even before he was born o_O.
once you get all 120 stars in this game, and talk to yoshi on top of the castle (theres a cannon by the lake you can get in), you get 100 lives, not only that, but your triple jump ooks cooler, and i've noticed that when you land, if you hold down the jump button you will "bounce".
My brother landed a triple jump in lava, and he "bounced" out of the lava, no damage!
it was so cool! just wanted to share this with you all.