Hums-to-Gods-in-Darkness

Special Equipment:

lots of moss, runes all over them. One has a nest on top of it.

Appearance:

The stone circle consists of two dozen and one large monoliths, an outer circle of twelve hewn of grey-black granite, the inner circle of twelve crystalline iron ore and the inner central monolith of pure black volcanic glass.
They used to be connected by paths forming arcane patterns, but those have long been overgrown.

Background:

The Brethren of the Red Chalice were an order of mages dedicated to increasing their own influence, but not of inherently evil bent - they were protective of those serving them, and actually samaritan towards their allies, even those neutral towards them, but should one have been deemed an enemy, he could expect anything from poison to a demonic visitation.
To aid their calculations concerning the movement of the stars, opening of astral gates and interpretation of portents, they erected a great stone circle above a powerful nexus of cosmic energies - deep below, a magma river took its course, while purest springs bubbled up from artesian wells, and all this was surrounded by a verdant forest abundant with all sorts of life.
Once enchanted, the stone circle was working well, but one Archmage, Dahlia the Coruscant, was still tdiscontent with its performance - most mages that used it did not understand all the function, fumbled up, and the results were imprecise, at other times, it was simply impossible to keep all the data and measurements in one's head, or have them laid out clearly before you. Then THE idea was sparked in her head by an apprentice complaing: 'about the big damned soul-less stone circle'. She smiled brightly, gave him a grateful kiss, and ran off, leaving the befuddled apprentice to his calculations (and she smiled, for now she had an excuse to invite him to her chambers when the sun set).
Dahlia gathered youngsters, twelve times twelve, and gathered them in the circle - by each of the stones, there stood five, and twenty-four by the central one. She instructed them to hold hands ... and burned them all with sorcerous fire. Even as their youthful souls were fleeing to the stars above, she gathered them and spun a greater mind of the matter, wiping all memories, but giving the potential for growth, learning and development.
The rest of her life, she spent teaching the stones, even while the order rose to greatness. When she died at the blessed age of 107 years, she was buried under the central stone, in a burial chamber filled with her artifacts and riches.
The stones had developed the persona of a youngster on the brink to manhood, curious, thoughtful, but, though enjoying the company of others, assertive and conscious of its superiority of spirit - and not too kind to let someone offending it by his stupidity feel it.
Besides calculations, the sorceress taught the stones how to enact a plethora of rituals, and how to schedule them, as well as many spells... She use the stones to predict the ebb and tide of manna, to divinate the fates of her fellows, or as a name generator for demons, probing the abyss to find one responding to the new-found name.
Even after Dahlia's death, the order profited greatly from the stone circle, but their power became too much for their enemies to stomach, and they allied, waging war against the mages. In their plight, the enemies set loose horrors even knowing of drives a man insane, demonic constructs of bone and rotten flesh, and great hydrae and raging salamanders, walking beside their armies.
The circle trapped them all, by cleverly designed spells, locking them away with the aid of the mages, but still, the wizards could not overcome the sheer numbers of their foes, and fell, one and all - but their victory was hollow, for neither they could enter the vaults the mages hoarded their treasures in, as the stones were warding them, and without the support of their supernatural allies they were unable to even mar the surface of Hums-to-Gods-in-Darkness.
So they went. And years passed, with the stones growing bored, and weaker - still they are virtually indestructible, but much of their power is gone, and do not let yourself be fooled - Hums-to-Gods-in-Darkness LIKES being powerful, and directing people around - but he needs a sacrifice a week, or a willing virgin sacrifice a year, or a unicorn for a decade, to be going at full power.

Recently, though, Hums-to-Gods-in-Darkness has begun to despair, for, with the shielding spells for the vaults still going, the entrapment of the vile beasts was beginning to fade - soon, they will emerge.
He wants to take revenge on those who slew his order, and wants to keep the tomb of his 'mother' safe too, but nothing goes without power. And you remember that apprentice from the start of the story? Yes, he sired a kid with the sorceress Dahlia, and that kid's descendat is still out there, and the circle knows it.

Roleplaying Notes:

Hums-to-Gods-in-Darkness has the personality of a somewhat playful, cocky, even arrogant at times intelligent mainframe. he cannot move, but he can possess any mage that passess the circle's boundaries, and act/speak through him. This is VERY hard to resist, but as soon as the victrim leaves the circle, he's free again.
The circle will get angry at stupid people very quickly, and is not that difficult to offend, either. And do not underestimate it only because it has not been fed for a century or two - it can still toss a few meteors around.
When idle, it will divinate the characters' futures, or at least try to, and then smile knowingly at them, or drop hints, for example about healthy food, or whom the character should 'mate' for the best offspring. Or which of the characters would be a good virgin sacrifice.
Most of all, it needs a few competent mages to re-enact the ritual to bind the beasts again, but it does not tell that all mages that are involved will die, their souls and bodies burned to ash...
If the characters are intent on looting the vaults or the grave, the circle will certainly not aid them ... but with the fading energy, soon the vaults will stand open - but of course, the PCs would have then to deal with all the horrors the failing wardings would unleash.
Other than that, the circle will try to lure promising wizards into its vicinity, to rebuild the order. Someone HAS to take care of the world, right?
A final note: what if some wizards hid in the vaults before their enemies struck? There will be artifacts that let you go without food, and provide for you, lots of armor, weapons, and knowledge ... if the PCs manage to persuade Hums-to-Gods-in-Darkness to let them inside a vault, then, in Fallout style, the descendants of those trapped there previously, will emerge, armed to the teeth, and with reasons to believe that what chased their ancestors down there is still lurking. For a twist, the PCs could be the descendants of the mages, finally set free. Or set loose?