Beyond the shores of Mata Nui lie a plethora of unique islands in the Great Ocean. Surrounding the Ocean is the Great Reef, a massive, mysterious undersea barrier.
The Island of Artakha, ruled by the being for which it is named, is a mythical land who’s existence is debated among Ko-Matoran scholars. It is said to lie beyond the great reef in a sea of silver protodermis where it is always day time. There wondrous inventions are made and the matoran there live happily. It is said that the master crafter of the island created the world along with his brother, Karzahni, and Ekimu and Makuta.
The Island of Karzahni, is a dreaded, shadowy land which surrounds the silver sea where Artakha lies. It is constantly covered in black clouds and home to matoran who haven’t done their job well. These matoran are tortured and mutated so they can no longer be recognized by their friends. The insane ruler of the island, Karzahni, is Artakha’s brother and created the world along with the three other gods. While the other three gods were responsible for creating the world, Karzahni was responsible for destroying the mistakes. The existence of his island is debated as well.
Mahri Nui was once a prospering island that traded with Mata Nui long before the cataclysms of Ekimu and Makuta’s rivalry. However, it grew too powerful and sought to conquer Mata Nui and defeat even the four great gods to gain control. It is said that, using their combined powers, the gods sunk Mahri Nui beneath the ocean and created a field of energy around it so no one could come out. Those who commit unpardonable crimes are also sent down to the depths of the massive aquatic city prison.
Odina(see G3 Dark Hunters)
Daxia/The Island of Light is a mystical island east of Mata Nui where the rumored Av-Matoran live. It is said that Ekimu rose up from its soil and blessed the island with constant daylight and the matoran with special powers. It is also said that the sun, which rises from there, is created in the massive mountain of light at the center of the island.
Destral/The Island of Shadow is a mystical island to the west of Mata Nui which is home to the shadow matoran(shadow matoran aren’t actually an element, their just a collection of different matoran), a secretive tribe that worships the Makuta. It is said that the dreaded Rahkshi were fused with their animals on the island and that Makuta dwells there. Rahi were first created on the island of shadow.
That’s all I have so far.