This is to be done in the Forest of Illusion 1. Basically what you do is come to the box with assorted power-ups. Get the star Power-up AND RUN AS IF YOUR LIFE DEPENDED ON IT! At the same time hit as many enemies as possible. You should start getting lives, at the end you should have goten about 20!

What's Cool in the GBA version Mario or Luigi depending on who you do it with will say a little comment!