Begin playing one of your game saves with a low battery charge on your remote to initiate a message from Cranky; he will warn that your battery is low and award you extra lives to help you out.
Bonus level
All levels in a world except for the Boss levels have hidden K, O, N, and G letters. Collect all four of those letters in all levels in a world to unlock a bonus level. There are a total of eight bonus levels.
Extra lives
Resume a game from a save with a Wiimote with a low battery. Cranky will warn you that your battery is low and give you three extra lives.
Hidden Music galleries
To unlock the following, complete the following tasks.
Gallery
How to unlock
Gallery: Beach music
Beat the Boss at the Beach section.
Gallery: Cave music
Beat the Boss at the Cave section.
Gallery: Cliff music
Beat the Boss at the Cliff section.
Gallery: Factory music
Beat the Boss at the Factory section.
Gallery: Forest music
Beat the Boss at the Forest section.
Gallery: Jungle music
Beat the Boss at the Jungle section.
Gallery: Ruins music
Beat the Boss at the Ruins section.
Gallery: Volcano music
Beat the Boss at the Volcano section.
Metroid - Ridley's head
In the silhouette level of the factory area, at the background of the factory equipment, you see the shape of Ridleys head.
More hits and rewards
When you collect your prize from the barrel at the end of the level, keep the Wiimote vertically and make punching motions to get multiple hits, and more rewards.
Rare Orb
Successfully complete the bonus level in a world.
World 9
Collect all eight Rare Orbs to unlock World 9, "The Golden Temple".
3 Extra Lives...