Instructions
Travel to Broque Madame's shop in Blubble Lake.
Speak to Broque Madame. She will tell you she's been experiencing some back pain and will ask for some help. Agree to help her, then select "Goomba Storm."
Turn your DS on its side so that the D-pad is on top, and the "A" and "B" buttons are below. When the challenge starts, a steady stream of Goombas will fall from the top of the screen.
Tap the corresponding button prompts as the Goombas pass by to remove them from the screen. The goal is get them all but, at the very least, the vertical perspective should help you miss less. Hitting 150 will net you a "B" ranking, while 250 will give you an "A," along with the Treasure Ring.