So I entered this on BZP, where I hope I interpreted the guidelines correctly. It is my first attempt at doing actual custom MOCing, and I think I succeeded. This is my best MOC so far IMO and I'm glad how it turned out.
Here is the description I gave him.
On the island of Okoto, tales are told of a being that stalks the twilight. The village elders name him, Nox, the thief of the night. The legends say that he comes when the mind is most vulnerable, after a great loss, or a great triumph. His presence is heralded by a chill air and a shiver in the spirit, then all light is extinguished. As a vampire feeds on blood, the creature feeds on the strong emotions given off by others, leaving his victims empty, and without purpose. In the past, hunts have been made in search of the devil, but all have been futile. However one hunter was able to come within view of the monster, describing it as a hideous amalgamtion that seemed to be ripping itself in two. He said that the right side of the body resembled the Mask Makers, but the left glowed blue with a terrible energy. He described the monster's words, how it hated itself and wished to depart in peace. With every step, it seemed to fade in and out of reality, only the right side keeping it anchored in the world. The hunter could not bring himself to end the creature, and departed shocked at what he had witnessed. But perhaps these are just fables and there is no Thief of the Night. However I am inclined to think otherwise.
So I will welcome criticism on the MOC as I really need to develop my MOCing abilities with constraction. Not sure if I'll do anything with the character itself in a story or other, but there's always the possibility.