To constantly have your shield up simply press the B button rapidly. This will keep you from taking damage from enemies, But you will still take damage from environmental hazards. (e.g. Lava, Swamps, etc.) Note: Do not hold down the B button because you will just start charging your Elemental energy and be vulnerable to attack.
Megablast
This cheat only works with Blue and Black. Hold B Press Y Right After You Charge Your Energy All The Way Up.
Le-Wahi
In this section, the camera automatically turns toward the next point of intrest. Just follow the way the camera to progress through the level.
Play as Takua Nuva
Successfully complete the game using all six Toa.
Extra bonuses
Complete a level with all Lightstones collected as each Toa to unlock a bonus at the Extras menu.
Defeating Makuta
When you are at the end of the game and are battling Makuta. press A(2), Y. You should be gliding and dodging all attacks except for the flying bees.