First as yoshi go to the bomb-omb battle field. Eat a goomba and make it an egg. Then Jump on another goomba and fire the egg at the same time. You will get an invisible box. Start walking around and things will start disapering. After some time (depends on your game) the game will freeze and to access the menu press l,r,left,and A at once. Then let go and hold down and b. Then let go and press start and select and you should be at the menu.
*Note* only works 75% of the time