nyx

As in case of most of the Old Corporations, we know only scraps. These are things recovered from the Abyssic Magma Breacher Ship, found orbiting the Anknor's system sun, the Septagram. Abyssic Magma's memory core was heavily damaged by the fire which consumed much of ship's interior but we were able to extract partial data from one of the backup memory crystals.

• Five Great Serpents speak through the Navigational Cortex. Do never question their wisdom. Let the termination of the Arch-Servant Nathaos sink in. Blasphemy will not be tolerated.
• We've lost the war. Our worlds were destroyed. They call us the vilest ones that ever existed. But remember - they are blind. We are the only ones who saw the enlightening flames of Hell. Now - only we remain. We must complete the circle.
• Admiral, the Master's signal has reached us. Yes, a single pulse, but the frequency was impossible to mistake with anything else. Yes, I understand. Our sacrifice will not go in vain.
• Prepare the beam to launch.

What do we know - or what do we suspect:

NYX sigil contains Five Great Serpents, as well as the Eye of the Abyss, along other symbols. We suspect that there are more, as no aspect of any Old Corporation was accidental.

They excelled at making Sleeper Agents. The Dreamer stated that they've made a 'perfect doppelganger'.

Their entire structure was built on lies and misinformation. And if they were deceiving themselves, we can be sure that everything projected by them outside was also not true. Thus, we cannot even believe any NYX-related relics or artifacts. Everything NYX-related must be treated with extreme caution.

Moreover, I personally think that they excelled at memetic warfare. Everything we know about their inner workings and their prowess at the field of biotech seems to confirm it. What scares me the most is the fact that they treated their own kin as lab rats. I cannot even imagine what they did to their enemies... 

They most likely encountered the Fallen Ones as the first humans ever, maybe except some cosmic eremites from the ancient past.