"Prototype"

History
"Prototype" was created when a Dark Hunter once had an experimental weapon (implied to be a Spear of Fusion, like the one Vezon carried), and fired it at two Toa (Fire and Earth) just as they were merging together into a Toa Kaita-like form. The result fused them permanently and drove them mad, and the new being went on a rampage and disappeared. Centuries later, he was found injured in a swamp; he was nursed back to health by the Hunters and recruited, given the codename "Prototype".

Tools, Powers, and Abilities
Prototype retained control over the elements of sonic and earth, and his organic parts decomposed to the point that he was mostly machine. He was incredibly powerful, but also quite smart. His life force was tied to his armor, but after so long it was almost impenetrable. Prototype was sometimes used as a practice target for rookie Hunters; if they survive a fight with him, then they can handle their missions. Prototype almost killed Zaktan in the Piraka Rebellion, but Vezok tricked him into abandoning his post.