On the level 4-2 go stand on the right side of the first falling platforms. Stand underneath the three blocks. Jump up and there will be hidden blocks. Climb on those blocks and hit the left block of the three. A beanstalk will appear. Climb it. You will now be in mushroom land with tons of coins! When you finish this small level, which has no enemies, you will come to a warp zone, where you'll have the chance to warp to the levels 6, 7, or 8.