Nynrah Ghosts

The Nynrah Ghosts were a group of approximately four dozen Matoran crafters from the island of Nynrah. The Nynrah Ghosts are the only known Fe-Matoran, (Matoran of Iron). Little is known about them, except that they modified the Makuta's armor when the Makuta evolved. They also created the Nynrah Ghostblasters, hence the name.

Other devices they made were the Exo-Toa, Zamor Launchers, and Fohrok. However, they secretly sabotaged the Fohrok, and upon learning of this, the Brotherhood of Makuta hired multiple Dark Hunters to execute the Matoran responsible. Eventually, only two Nynrah Ghosts were left. One of them became a Dark Hunter named Phantom while the other left to Stelt as a rouge Ghost. He modified Vultraz's Skyfighter and, due to his slow response to Mazeka, now does not have a mask as Mazeka crushed it.

Dark Mirror
In the Parallel Universe, the Nynrah Ghosts were wiped out by a team of Toa led by Nidhiki because they were making something that could be a threat to the Toa Empire.

The Kingdom
They evacuated to Mata Nui after the Great Spirit's death and still play at secrecy. One Nynrah Ghost gave Takanuva his Power Lance and Midak Skyblaster. Another Nynrah Ghost became part of Turaga Takanuva's ruling council.