Go to Valley of Bowser 4 with a Yoshi before you enter the level. It also helps to be caped. Go through the level until you encounter the block with a vine that is after a lava section. Jump onto the block and then jump at the wall. When you hit the wall, jump off of Yoshi (hit A) and jump to the right. You should land on top of the wall, but the camera won't follow you. Now, walk to the right and you'll fall through the wall to your death.
Submitted by: SolarCloud