This fantastic cheat will get you 99 lives easily -- you can always return for more! Go to the Supermassive Galaxy in World 4 and choose the first Star challenge. Play through the level until you get to the hockey puck-shaped planet with three supermassive Koopa turtles patrolling it. DO NOT grab the Spin Drill -- you'll have to get hit to lose it if you do! Run up behind a Koopa and long-jump (press Z while running and then press JUMP) onto its back. You need to long-jump from about a turtle-shell-length behind it to catch the "sweet spot." Continue to hold the analog stick to the RIGHT and hold JUMP to continually bounce off the Koopa's shell. If you fall off or hit the head, try again. If you hold these buttons you should be able to maintain momentum while constantly bouncing on the shell. After a few bounces you'll rack up 1-Ups for each hit.