Karzahni was also known to be as powerful as Teridax but whereas Teridax was considered as pure evil, Karzahni himself was completely insane.
Around 100,000 years ago, Karzahni was created alongside his brother, Artakha by the Great Beings. Soon after their creation, the two beings fought for the Mask of Creation. Soon after the battle, Karzahni was lost and he was banished into the island, which he created and named it after his name.
While Artakha chose to make a heavenly island for good Matoran workers, Karzahni chose to take in the bad ones, intending to repair their faults and return them to their homelands. However, his ability to fix the Matoran was not up to par, and he completely rebuilt the Matoran, but into weaker forms. To compensate for his inability to properly repair the Matoran, he gave each of them weapons. He then sent them to the Southern Continent to make sure his failures would not be discovered.
The Turaga eventually noticed that Matoran sent to Karzahni never returned from their exile, and stopped sending their poor workers. Angered by the lack of Matoran coming to him, Karzahni went into denial, blaming the Matoran for his failures. He refused to send any more Matoran away and trapped them within his realm, replacing their masks with his own twisted designs, stripping them of their identities.
Quest in Mahri Nui
It was sometimes during the Great Cataclysm struck the Great Spirit and when Teridax was defeated and Imprisoned by the Toa Metru, Karzahni immediately knows the existance of both Mata Nui and Teridax and he leaves his post in his island in search of power.
At the meantime in elsewhere, the prison called the Pit was heavily damaged and the warlords called the Barraki escape into the ocean, where they transformed into their monstrous forms and at the same time, Karzahni went into the ocean in the search of the Kanohi Ignika. When Pridak wa