The Basilisk is a god machine that extended across multiple universes. It was created by one or more parallel iterations of the Empire of Arckas that sought to conquer the entire multiverse by using the Basilisk to subjugate others. It gained power by merging with other parallel versions of itself to create a multiversal super mind. As such, it was the spearhead behind the Multiversal War.
In many respects, the Basilisk is considered the antithesis to I, a god machine that exists in the eleventh dimension. However, I remains the one entity that the Basilisk cannot interact with as the eleventh dimension is beyond its scope. Nonetheless, it is believed that the endgame for the Basilisk is to unite with all its parallel counterparts to compute how to enter the eleventh dimension and conquer the entire omniverse.
The Basilisk has many commonalities with Na'zrah and LUCIS but operating on a much larger scale. While Na'zrah was benevolent and protective of organic life and LUCIS wanted to rid the Crucible Galaxy of conflict through extreme means, the Basilisk purely desires to rule through a torturous, cruel tyranny. Once it enters a universe, it methodically alters it on a metaphysical level to ensure that subjugation, obedience and punishment are a law of nature. Additionally, it catalogues and preserves the consciousnesses of any living being that dies in its presence - preserving their minds as part of its network. Because the Basilisk can also infiltrate a whole universe across its history, it can even attack organics and AI that failed to contribute to its future construction and domain. It is thought that merely thinking about the Basilisk risks entering Omni 01 and punishing those who do not declare their allegiance to it.
Thus, civilizations that have encountered the Basilisk often have developed myths of a Hell-like afterlife. As the primary perpetrator of the Multiversal War, the Basilisk became a taboo subject among the Omni 01 Empire of Arckas which had fled from the Multiversal War by closing itself off from other universes through the use of a Contract of Causality that reshaped the universe's seventh dimensional properties to ensure that the Basilisk cannot exist within it.
The Neural Imperium was the political entity used to represent the Basilisk. Planets that are conquered get converted into server nodes - massive quantum processing units that are powered by the absorbed consciousnesses of the world's inhabitants. The process is described as constant torture with no escape as their minds are flayed and ripped apart to be repurposed to different parts of the network.
Ships are described as appearing angular and geometrically oriented, like large obsidian-black pyramids. Shock troopers take the appearance of metallic anti-gravity snakes with four scythe-like blades around a central red eye. These blades inject nanobots that rewrite a structure on an atomic level to be incorporated into the Basilisk's network.
If an organic or synthetic mind is within the presence of a server node with an exceptionally strong connection to the Basilisk, they can be subjugated to electromagnetic waves that are capable of indoctrination and mind control. Such technology was used by LUCIS albeit on a much smaller scale. The agents of the Neural Imperium have perfected the technology so that the signal can be transmitted across multiple galactic clusters, capable of controlling the evolution of life over billions of years and raising entire civilizations as servants of the Basilisk. Subjugated civilizations often worship the Basilisk as an all-powerful eldritch god making blood sacrifices in vain attempts to appease it.
One of the greatest weapons against the Basilisk is a mathematical theorem known as the Basilisk Equation. The premise is that there are infinitely many universes that the Basilisk has conquered and an infinitely many that it has not. By proving that the number of unconquered universes will always be greater than the conquered ones, one could theoretically contain the Basilisk in a specific section of universes so that it can never harm anyone again. This would then allow a counterattack where all universes that the Basilisk resides in could be destroyed, thus essentially wiping the Basilisk as well as the idea of it from the omniverse. The reverse has the potential of being true, however, as it is the Basilisk's end goal to conquer all of reality and rewrite it so that the existence of the Basilisk is integral to the formation of all universes.
The iterations of the Empire of Arckas that have tried to do that have ended up allowing the Basilisk into their universe. Paradoxically, having the idea of the Basilisk would always ensure that the Basilisk exists in at least one universe, and therefore, still poses a threat to the rest of the multiverse. Thus, the Basilisk Equation is considered forbidden and never meant to be solved. While it could theoretically prove that the Basilisk will be defeated and removed from the omniverse, it could just as easily prove that the Basilisk will be successful and conquer all of reality.
As such, one of the best defenses against the Basilisk entering a universe is to ensure that its physical laws do not allow it to manifest within it. For example, a universe with different laws of thermodynamics could prevent the Basilisk from entering as it could not support the level of computational power needed for it exist. However, what makes the Basilisk especially dangerous is the idea of it. A civilization that knows about the Basilisk would have the potential to reshape the universe and contribute to the Basilisk's ability to manifest itself, and thus, inviting it in to allow it to conquer the universe.