New Super Mario Bros. Wii: 3-4 Replay -- Almost Impossible to Fail

Now that the switch has be activated, this level becomes much easier. You reach it after completing 3-5. New features with this switch include the fact that it can be activated from the map (no going through another level to reach it) and it can be deactivated. We're going to leave it activated because you cannot progress without it. With the blocks filled in, almost all gaps leading to the void are covered up. It is also easier to dodge some enemies and the paths allow you to avoid difficult areas, such as that immediately past the midgate. Finally, a red pipe is accessible, which takes you to the main goal (black flag), allowing you to progress to the castle. I got this within 2 tries playing solo.