Necrosis

Necrosis
Necrosis was a being originating from a plane of shadows. He served another shadow entity named Mother, leading an army of zombie shadow Toa in an assault on New Atero under her direction. After the assault failed Necrosis went off on his own, seeking an artifact called the Ordon in an attempt to become omnipotent. His wish was granted, but he was seemingly killed in the process. He would later return, only to encounter the "end of the world" he'd been seeking for so long.

Early Life
Long, long ago, in another dimension, shadow Toa were created naturally, but the Makuta were afraid of them, fearing that they would one day replace them as protectors of the Matoran. They finally convinced the Hand of Artahka to seal them away in a pocket between dimensions. There, there was no light to contrast the shadow, preventing them from escaping via shadow-travel. One such shadow Toa, Necrosis, caught onto the heel of an inter-dimensional merchant as he passed through the pocket, and was dragged out of the void, being thrown thru dimensions.

Demon Of New Atero
Once he escaped, Necrosis intruded onto Universe-31 (TNC's universe), and attacked New Atero, first killing a large amount of Matoran hiding in shelters from the Po-Koro attack (enacted by the Chaos Legion) and later still using an army of continously regenerating shadow beings to try and destroy it. However, he was attacked and injured by Sylah and Shadus, retreating to avoid fatal injury and opening a portal for his brethren in the pocket void-dimension.

A large battle ensued, with the Shadow army having the upper hand until a lone Toa, Spordan, sacrificed himself to kill Mother, breaking the spirit of the army and forcing Necrosis to retreat as the rest of his kind were slain by a mysterious new Toa, Impora, who would go on to later aid the Toa of New Atero before disappearing as well.

The Ordon
Sometime later, Necrosis managed to convince Velika to give him a small force of allies, to retrieve a mystical device from a temple nearby, the Ordon.

Escaping with the device, Necrosis used the wish-device to become a fullbred Makuta, and to restore his former leader, Mother, into a hammer-like weapon. He called on Torok, briefly consulting him for advice on what to make his third wish, before Torok left, seemingly uninterested in him.

He later lured "Toa" Sylah to the Makuro HQ (a high tech tower in the city) and attempted to force her to join him, exposing her to a vision of her former life as a Matoran and gloating about his power.

Torok appeared and attempted to break the vision, incensing Necrosis to use the third wish to become a being like Torok. Unbeknownst to him, Kirathel, also having a deal with Torok, also used the Ordon at the same time, splitting the divine power between both entities and causing Necrosis to seemingly evaporate from the overload of power.

Discovering the Truth
Necrosis, having survived his transformation and become a being like Torok (down to choosing a Matoran-like form), briefly wandered the world, coming to understand his power. He met Kirathel briefly, and conversed with her about a "coming darkness". He later met up with the being Onisani, a Toa hunter from another world who could absorb and negate Elemental attacks (and had used this power to slay an entire team of Toa earlier). The two joined forces, before wandering near a Suva where the Toa of New Atero were fighting two of the Chaos Legion, Hanah and Hunter.

Though initially intending to watch, Necrosis detected a portal opening above the battlefield, summoned by Rahzahkea, and was telepathically able to deduce not only the Wrathbringer's origin, but also that of a second entity. The combined knowledge of two beings similar to Torok, along with the psychic feedback from both deities, was enough to overwhelm the nascent god-Necrosis' mind, causing him and Onisani to spontaneously disintegrate.

It is unknown what happened to either of them after that, though it is assumed they are dead.

Personality and Traits
Necrosis displayed both arrogance and sadistic tendencies, believing himself a superior being to the inhabitants of New Atero and avidly attempting to conquer them, as well as killing multiple Matoran for no given reason. It can be assumed his hate of Matoran, as well as Toa, stems from being imprisoned at the Makuta of his world's orders.

He also hated being powerless, which drove him to seek out the Ordon and use it to gain power when threatened by Torok.

While transformed, and possessing some form of cosmic awareness, Necrosis demonstrated a much calmer exterior persona, acting like he knew more than he let on and not deliberately engaging in fights with anyone.

Powers and Abilities
While a Shadow Toa, Necrosis possessed all the powers of a normal Shadow Toa, such as Shadow Manipulation and Creation, as well as a shadow-based teleportation power. He also worn a specialized Tryna, that could turn corpses into superpowered constructs of shadow, that could not be destroyed naturally unless the mask itself was disrupted during use.

As a Makuta, Necrosis possessed all the powers of a normal Makuta.

While a deific being, Necrosis demonstrated some form of Matter Manipulation, Cosmic Awareness like Torok, and Teleportation. It is likely he possessed more powers, but did not use them prior to his apparent demise.

Trivia
Prior to his death, Necrosis was the fourth villain the Vanguard initially fought, preceded by Marendar, the Empire, and the Chaos Legion.

Necrosis' ultimate fate is uncertain, as the Wrathbringer has demonstrated a power to revive those it slays as minion entities, although due to his power, it is unlikely the near-mindless Wrathbringer would be able to do this effectively.

It is unknown what the other entity Necrosis saw was.