Unlock Takua Nuva
Win the entire game using all 6 Toas.

Unlock extras
Get all lightstones with each Toa to unlock an item in your extras menu.

Defeating the Brown Rakhshi
To defeat the Brown Rakhshi, corner him on one of the floating wood raft-like objects. Then, shoot that one with elemental energy and you will win the level. Note: This is sometimes difficult to do.

Dodging attacks and refilling your Mana
When getting attacked (this works well when facing more than one opponent), jump and use your shield rapidly. The attack will completely miss and you will refill your Mana. Note: Do not do this with dragonflies and other flying enemies. It may work, but there is less chance of it working. For extra effect, while in the air press (Attack). Since enemies are vulnerable when they attack you, they will get serious damage.

Easy wins
Rapidly press / to keep your shield on. Then, walk and fire. You will win. Note: This does not work on some Bosses.