A baby Yoshisaurus Rex! He would attack the person who came up there and the others would scream and run away.
No, no... better yet... Miyamoto! Hee hee. Or Charles Martinet. Both of them up them maybe? They could be relaxing on the roof in recliners, just chilling out and waiting for someone to come up there and recieve their prize... of lemonade. To be serious I think there could just be a different color Yoshi that gives it to you.
Oh crud, I think I know what they're going to do! There will probably be some big stupid present behind the main tower that has the 100 lives/special jump inside and a note on top that says what Yoshi says. Anyone agree with me here?
On November 21st, Nintendo will unleash the greatest handheld system on America that this world has ever seen. Two screens, two extra buttons, one touch-sensitive screen, wireless multiplayer, voice recognition, and more. Prepare to severely wet yourself.