In 2-7 (Lakitu's Wall), eat at least one fat Shy Guy to give Yoshi a huge egg. Go through the course up to the part with the Message Block and the car morph bubble item. Shoot the big egg straight up at the Message Block. The egg will hit the block twice, causing the screen to go crazy. Yoshi will disappear, the stars will come to the foreground, and you might even get a small message text box lingering on the screen. Even though Yoshi is gone, you can still move around. For a real challenge, try finishing the level! The game will freeze up if you make it through the goal ring, however.