Free Lives!
In World 1-2, go passed the first Koopa to the raised platform with the next Koopa and a Goomba. Nix the Goomba first, then steal the Koopa's shell by jumping on it. Turn to face the back wall (while you're on the platform) in front of the three blocks. Chuck the Koopa and jump straight after. As long as you don't touch anything, you should bounce up and down on the Koopa shell while it ricochets endlessly against the back wall, scoring loads of lives.
Reveal Rosalina
Conquer the Star World Super Galaxy to unlock Rosalina. You'll be glad you did - she has an awesome spin attack.

Did you know? In some parts, if you blow on the Wii U mic, you can repel enemies!