There is a spirit that comes from before the foundation of the world of DARK•HERITAGE, but which lingers still nonetheless. This spirit is sometimes called Grigori, the Watcher, and it is primarily known as being a spirit of hunger. No one knows for sure how Grigori came to be such a near-personification of appetite, but it is so today.
Now, Grigori comes shrieking and howling from the highlands in the mountains when winter thunderstorms rage throughout the peaks. If he finds a person, alone and unprotected, he can possess that person, and reshape his body into a fearsome form, full of muscles, sinews, teeth and claws. He's often been described as centaur-like, and with gigantic antlers, although other descriptions have, at times, been given as well.
When this happens, all who live in the area need beware, for Grigori, now embodied, goes on an orgy of rape, violence and hunger, killing all in the area before his host body dies from the strain (this usually only takes a few days, luckily.) It is possible, although extremely difficult, to kill Grigori's host body, which expels the spirit and banishes it back to its frozen mountain haunts again for a time, but Grigori is immortal and immune to any weapon or magic that men can wield--only his possessed body is vulnerable, and even then, not very. While possessed, a mortal body becomes terrifyingly potent--strong, nearly invincible and horrible. An entire squadron of tough mercenaries was known to have been killed by The Watcher, their desecrated and violated bodies and body parts strewn across a snow-covered landscape to be found several days later by another patrol. This took place in the Caurs Mountains during the reign of King Guilhem Huc des Peyrasmortas, during one of the interminable border squabbles between nobles in the area. The incident raised awareness of the Watcher amongst the members of the King's Inquisition--which was a slightly different organization than the one formed later by Huc des Peyrasmortas descendant following the scandal of the only public performance of "The King in Yellow" and the King's only brother revealed as a demoniac heretic. Secretive scholars have tracked incidents that match the modus operandi of Grigori, and cataloged them, although such records are kept under lock and key at the Academies at Razina and Terassa. Rumored copies in the hands of private collectors, and floating around somewhere in Porto Liure also abound.
Reports of Grigori's activities range rather widely in the circum-Mezzovian region, but always come from high in the mountains, and fierce thunderstorms and the advent of cold weather seem to be a common correlating theme. Professor Alfons Gombal of Razina believes that Grigori goes into long periods of torpor where he attempts to rejoin his brothers in the mountains, or at least replicate the conditions that he enjoyed in Kadath before his exile. He cannot return to Kadath, or even come near it, so he languishes in what mountains he can climb.
Although not meant to be a reflection of such, Grigori can best be represented in d20 by the Lord of the Feast, a creature detailed in Privateer Press's Monsternomicon II. For other systems, such as m20, you will have to convert as best you can, based on the detail given here--although, of course, one of the main attractions of m20 is that you can use d20 material more or less as is.