The Rahi Nui was a bizarre creature that appeared to be a combination of a Muaka, a Tarakava, a Nui-Jaga, a Nui-Rama, and a Kane-Ra. It was created by Makuta to serve as a tracking beast for the Dark Hunters Nidhiki and Krekka. Its natural tools were horns, wings, teeth, power forelegs, and hindlegs. It also originally possessed all the base Kanoka disk powers, including teleportation. Using that particular ability, it could home in on Toa wherever they might be. The Rahi Nui fed on Toa power, making it immune to elemental blasts. The first recorded encounter with the Rahi Nui was with the Toa Metru, who defeated it and caused its atoms to disperse. Over 1,000 years later, it appeared on Mata Nui, minus its special powers. The Toa Nuva and Vakama defeated it, after which its whereabouts became unknown.
According to Turaga Vakama, not even the Bohrok-Kal could tame the Rahi Nui. Even at the height of the Toa Nuva's powers, they could not hope to defeat it, only contain it. It was created for one purpose: to defeat Toa.
Turaga Vakama once recited the words of an ancient text from memory: "Beware the Rahi Nui...beware the beast of horns and claws, who stalks land, sea, and air. Born to seek the Toa, it will bring down all the works of Matoran in its path. You will know it by its roar, by the shaking of the ground as it strides, by the fierce glow in its eyes. Guard well against it, or it shall be the end of all."
The Rahi Nui could let loose a roar so loud it could almost knock the Toa off their feet. It was bigger than anything and of the Toa Nuva had ever seen, being at least three times the size of a Toa. The head of the beast was that of a Kane-Ra, with long, sharp horns that could pierce solid rock with ease. Its forelegs were those of the Tarakava, whose powerful arms could deliver a stunning blow to even a Takea shark. Its body and hind legs were those of Muaka, whose powerful claws could shred solid protodermis. It also possessed the stinging scorpion-like tail of the Nui-Jaga, and a larger version of the Nui-Rama's insectoid wings.
It was strong enough to send Tahu Nuva flying by charging into the shield projected by his Hau Nuva. According to Vakama, it was bred for power, not intelligence.
It did not wear an infected Kanohi Mask. Makuta had no need to control it with one, since it hated Toa and all who stood with them.
The Rahi Nui was a monstrous hybrid creature with the head of a Kane-Ra, the forearms of a Tarakava, the body and hind legs of a Muaka, the wings of a Nui-Rama, and the tail stinger of a Nui-Jaga. When first encountered by the Toa Metru, it also possessed all six [sic, eight] basic Kanoka disk powers.
The Rahi Nui was a monstrous hybrid creature with the abilities and natural tools of five other beasts. It also had the ability to feed on the Toa's elemental energies and use that energy to grow bigger. When it grew, it did not grow heavier.