My Lord: I recently recorded the first references to the night demons called the “mara.” (And, incidentally, my use of the term “night demon” is intentional–there are other kinds so I find it worth the trouble differentiating one from another.) They are indeed a breed to be feared–animated shadows even a shade darker than the deeps of the Twilight, slinking through the night like a poisoned breath. But, I recently was able to speak quietly with one or two people who know a bit about their limits.
Ironically, light in general does not seem to be much of an impediment to them. A normally-lit room, or a cloudy day simply makes them stand out in starker relief. However, they abhor direct sunlight or fire, and both seem to burn them. Being shadows themselves, they can quickly retreat into a shade cast by something else. This allows them to travel, albeit with difficulty, in the sunlit lands by slipping from shadow to shadow along the way. My informant did tell me that on several occasions mara have been trapped by luring them into a shadow and then quickly surrounding it with very bright light. The shadow becomes like an island in a sea of flame to them, and they dare not leave their haven.
The mara’s greatest weaknesses (that these people apparently know of) is mental. They are ravenous in their taste for blood–something I do not yet understand since by all accounts they cannot consume it–and they will do virtually anything for it. This can sometimes be played off against their other driving force, which is their servitude to the starsisters. The former is consistently willing to betray the latter, and the latter is always seeking to indulge the former in any way it can in the service of its mistresses.
I am not sure that this isn’t a “weakness” in only an academic sense. It would be a very dangerous fate to tempt to even speak to a mara, let alone try to game one. I do not look to try it myself.