Iden

"Only [Matoro's] body is over there. His spirit is floating in the air over here, and no, I don't know how it happened. Matoro thinks it has something to do with his mask."

- Hahli, BIONICLE Legends 3: Power Play

The Kanohi Iden was the Mask of Spirit.

Powers
The Kanohi Iden gave its user the power to temporarily release their spirit from their body. When released, the user's spirit was undetectable, and their physical body went limp; the user's spirit could move at high speeds while released. The only beings who could see and communicate with an Iden-user's spirit were Elda or Rode-wearers.

An Iden-user's body will appear dead while their spirit is unleashed. When a being was in their spirit form, their physical body was vulnerable, as they couldn't protect it. Because spirits cannot survive without a body, if an Iden-user's body is placed in stasis, their spirit will eventually fade away. The same is true if a user's spirit were to encounter Voporak's time field.

In spirit form, a being could not affect the physical world. This included accessing their Element, as that required a union of the mind and body. However, a Toa's powers were tied to their spirit, so if an Iden-using Toa went into another body, the body would have the spirit's elemental powers. Additionally, an Iden-user could possess living (but spiritless) bodies or self-powered robots.

Example Usage
Toa Matoro used his Iden to secretly communicate with Hahli in the midst of battle with the Piraka in BIONICLE Legends 3: Power Play.

Great

 * Toa Inika Matoro - Formerly; transformed into his Tryna by the Ignika when he became a Toa Mahri.

Powerless

 * Matoran Matoro - Formerly; changed into an organic Great version when he became a Toa Inika.

Trivia

 * If an Iden-user possesses a corpse while a Tryna-user focuses their power on the deceased body, they can work together to mimic the deceased being.