Necros Nui

Necros Nui is a deadly wasteland near the Matoran Universe's southern continent.

History
Necros Nui was once referred to by another name, which has now been lost to history, and occupied by Matoran and the Skakdi race, who had been relatively peaceful in this age before Spiriah's experimentats on them. The Great Beings had set up a vast machine on the largest island island in the chain to access the other worlds that they had made to tie to the Matoran Universe, such as the Elemental Zones or the Backup Dimension. However, a few ambitious scientists, Makuta and Matoran alike, began to experiement with the mechanics. Their incompetence at the machines workings opened up a temporal hole to a dead world that began to leak a deadly radiation into the Matoran Universe, altering the forms of the beings that lived there. Many changed into twisted mockeries of the beings who released them; these beings were referred to centuries later as the Demo-Makuta. The Makuta attempted to reverse the portal, or at least cause it to open onto another world to stop the temporal mutations, but the systems had been jammed by the corrosive energies relased from it. Many of the island's Matoran died or were changed into hideous creatures that would never again be able to live with their fellow beings, and most of the Skakdi fled before their territories were hit as well, though some were mutated as the other creatures were, though into more intelligent and malicious forms. These creatures, now forever changed into what would later be referred to as the Demons or the Corruption, were eventually forced back through the portal by a Brotherhood army, as the Makuta and Rahkshi were the only beings who could stay in the Corruption raditaion for an extended (but not infinite) period of time without being mutated. The portal was then shut by Zeko, the sole member of the group of scientists who had opened the portal who had stayed alive and largely unchanged through the entire ordeal. Its source stopped, the Corruption radiation died down, eventually ceasing to expand into the world and settling where it had fallen. The islands lost their individual names, and were forever after referred to as Necros Nui, the Great Decay. After the Great Disruption, Zeko was given this region to watch over, very likely as a punishment for what he and the others of his group had done.

The Escape
Millenia later, the creatures trapped behind the portal figured out a way to re-enter the world, and escaped back into Necros Nui. Zeko witnessed their arrival, and quickly reclosed the gateway, but not before most of the Demo-Makuta had been released once more. Their exposure to the radiation of the dead world for those many years had changed them into beings both like and horrendously unlike what they had seen in the Matoran Universe in their original mutation. Zeko managed to close the portal, but not before most of the Demo-Makuta had escaped back into the world.