Krana-Kal were specialized Krana, mutated by the Bahrag's energy and a mutagenic substance. Like regular Krana that were literally the brains of the Bohrok, the Bohrok-Kal were controlled by the Krana-Kal. The Krana-Kal were unlike the other Krana in that they could act independently, without depending on the Bahrag, and were able to communicate with other beings using telepathy. Krana-Kal also had a unique property that allowed them to turn from a different metallic/opalescent color to a high polish silver color and generate an impenetrable shield around their hosts when at the final stages of their mission.
The Toa Nuva defeated the Bohrok-Kal by overloading their powers with the Nuva Symbols. The Bohrok-Kal were destroyed, with only the Krana-Kal remaining intact.
Xa-Kal: Liberator Krana, the most important of the Krana-Kal, one of these needed to be be brought into physical contact with the Bahrag to complete the Bohrok-Kal's mission.
Za-Kal: Overseer Krana that could communicate telepathically with other Krana-Kal and had the limited ability to read minds and sense strong emotions.
Vu-Kal: Transporter Krana that could move its Bohrok-Kal host over the surface or through the air at great speed.
Ca-Kal: Seeker Krana that were linked to the Bahrag and could sense their presence within a limited range.
Yo-Kal: Excavator Krana that could sense stress points in the earth and detect underground movement.
Ja-Kal: Tracker Krana that could detect distant obstacles and enhance all of the senses of the Bohrok-Kal, especially hearing and smell.
Su-Kal: Demolisher Krana that could provide tremendous strength, endurance and resistance to heat and cold.
Bo-Kal: Visionary Krana that could see in the dark and tunnel through any substance except for the floors and walls of the Mata Nui underground.