Fail a level 8 times and the game will give you the option to turn on an "Auto Pilot" mode in which Mario completes the level on his own. This appears as a Super Guide block at the beginning of the level. Hit it to activate the mode.

Collect all three Star Coins on a particular level to unlock the Hint Movie for that level. This Hint Movie reveals the developer's best chops at New Super Mario Bros. Wii -- how to get infinite 1-Ups, secrets and Star Coins.