Nigthmaers (yes I want to spell it like this because it has "aer" in it, which is basically acient way of saying "air").

There is not a lot known about these ghostly creates besides endless legends and myths. They are said to come from a distant gas giant, full of dust and an atmosphere of pure magic (hallucinogenic atmophere). These creates can live in our heads, ships, builds, and even our friends. They are said to be able to travel the minds of others and imitate what they can perceive. Before time itself Nightmaers have lived in quiet, but something has now triggered them. In the fall of the Endless it is you who will find out why.

And the main quest will eventually reveal that the Nightmears are pure gas & dust, that the Endless used them to power their tech, and that their purpose is to findout where the last Endless lives (everyone tortured by them was just a means to get information).

Their main points are that they can hid/camouflage their ships or cities, copy abilities from other factions, and that they are religious and worship their home planet.