Kraahkan

The Kanohi Kraahkan was the Great Mask of Shadows, a mask of incredible power. It was made and kept in Artahka untill it was stolen by the Makuta.

When Teridax and Takanuva merged to form Takutanuva, the Kraahkan and Avohkii also merged, forming a mask with the powers of both Light and Shadow, or unofficially known as the Mask of Light and Darkness by Greg Farshtey. However, the two beings and their masks soon split apart again.

After the Piraka reached Mata Nui, Reidak threw the Kraahkan into the water surrounding Metru Nui because when he picked it up, it kept blasting him with Shadow energy.

Sometime after this, Makuta Icarax dived into the Silver Sea and emerged with the Kanohi Kraahkan. He then replaced his old mask with it.

Powers
It allowed the user to control the shadows and feed fear and/or anger into those affected by its power. It is made out of Protosteel, and can also gave the user the ability to see the darkness in the souls of others. The Kraahkan also changed shape - it was transformed to look like a Hau at least twice.

Trivia

 * There is only one Kraahkan.
 * In Dark Mirror, the Kraahkan was displayed unguarded in the Archives as a trophy, and as an insult to Teridax.