So, everyone knows the deal with spirits: you make sacrifices to them, and unless you've done something to really piss them off then they'll give you stuff in return. But why should it always be humans who do the sacrificing, and spirits who receive the sacrifices? Think of all the power they must contain, those spirits, glutted with centuries worth of offerings. What would happen if, instead of you sacrificing things to a spirit, you sacrificed a spirit to yourself?
It's been tried. It didn't exactly work out well.
Long ago, far to the south, there was a kingdom whose people worshipped an insect-spirit which took the form of a giant scarab beetle. (They probably worshipped other spirits or gods as well. It's not important any more.) Over the centuries, their priest-kings had developed very good relations with this scarab-god. In times of dire need, they would make enormous offerings upon its altar; and, in exchange, it would take on physical form and come to fight for them in the form of a monstrous scarab beetle, ten feet tall and virtually indestructible. The people revered the great scarab, and the spirit grew fat upon their sacrifices.
Well: times passed, and upon the borders of this kingdom arose a new empire, determined to subdue all rivals to its power. When the invasion came, the reigning queen called forth the scarab-beast, just as her ancestors had done; but the armies of the empire were fierce and numerous, and even a giant unkillable beetle-monster can only do so much. Day by day, the queen saw her armies pushed back, her territories shrinking, until finally her royal capital itself came under siege. One day the invaders tried to storm the gates; and when the scarab-beast limped back to her temple-palace after seven hours of fighting, covered in wounds and missing two legs and one mandible and bleeding horrible ichor all over the stone floor, the queen lost faith in it altogether. She led it down to the sacrificial chamber, which - as usual - was full of fresh sacrifices for it, bidding it climb up upon the altar to feast and regain its strength. Then she sealed the doors, poured several barrels of oil all over it, sat in the sacred seat normally reserved for the spirit itself, recited the prayer of sacrifice (substituting her own name for that of the deity), and burned the scarab-beast alive.
When the spirit died, all the insects for a hundred miles around went mad. The invading armies were driven back by endless swarms of stinging flies; the kingdom's inhabitants soon followed, fleeing their homeland in all directions, bearing with them stories of locust swarms so vast that they blocked out the sun, and insect-monsters the size of houses burrowing out of the swarming earth. For many years it was assumed that the whole nation had either fled or perished, destroyed by the hubris of its queen; but when the first scouts started to creep back across the borders, they found something far stranger than mere heaps of old corpses. The villages, towns, and cities lay abandoned, but beside them stood immense mounds of earth; and in these mounds dwelt a bizarre race of scarab-people, who spoke an approximation of the language of the old kingdom in bizarre voices composed of clicks and hums. They seemed to have no memory of ever having been human; they lived peacefully enough, using giant beetles as beasts of burden, and devoted all those energies not required for their own survival to the construction of great idols of their goddess, who seemed to be the only being they regarded as worthy of their worship. The idols always depicted the same thing: a woman of regal stature with the head of a scarab beetle. They called her the Insect Queen.
Is she still in there, in the ruins of the old temple-palace? Occasionally a band of adventurers tries to find out; but the closer they come to what was once the capital city, the larger and more aggressive the swarms of giant beetles become. Wise parties content themselves with just looting a few old shrines; the Scarab Men care nothing for the worship of any being other than the Insect Queen, and will look on in bemused indifference as teams of adventurers hack the gold and jewels from the ancient temples their ancestors erected to other gods. Foolish ones insist on pressing on towards the old capital, even after having half their expedition eaten by mindlessly aggressive scarab beetles the size of oxen. They don't come back.
The Scarab Men have sent an embassy to the Wicked City. This has not happened before. The Ambassador and her entourage have become one of the curious sights of the city, riding through its streets on palanquins balanced on the chitinous backs of giant beetles, on their way to discuss who knows what with the Ministers on the upper floors of the King's Tower. In their spare time (which is plentiful), they sit around carving endless icons of their goddess out of whatever material comes to hand; the embassy building is full of them, now, covering every flat surface, perched precariously in tiny alcoves or over-crowded shelves. The scarab-men just keep making more of the damn things. Anyone who breaks one gets fed to the giant beetles.
You can play a scarab-man, if you like. Treat them as fighters, except that they cannot perform feats of strength, gain +1 AC from their hard carapace, and take 1 extra damage per hit from bludgeoning attacks. They can wear any armour, but it will need to be made specially to fit their unusual body shape.
Scarab-men have very poor vision (-1 to ranged attack rolls), but can sense nearby movement with their antennae. They have a secondary pair of vestigial arms, with half the length (and half the strength) of their main ones, ending in small three-fingered hands; these arms can be used for holding things (lanterns, for example), but are useless for combat. They also have beautiful iridescent wings, which are totally incapable of actually lifting them off the ground. They can eat virtually anything, including dung and carrion, but their companions will probably prefer not to watch them do it...
All scarab-men have an instinctive, ancestral reverence to the Insect Queen. Any scarab-man who sees someone deliberately damage one of her statues or defile one of her temples will fly into a hysterical rage and attack them until either the scarab-man or the defiler is dead.
Starting equipment: Chainmail cuirass (AC +5), heavy shield (+2 AC), heavy mace (1d8 damage), crossbow (1d8 damage, 2 rounds to reload), holy symbol of the Insect Queen, tiny idol of the Insect Queen, hymns and scriptures of the Insect Queen, weird trinkets worth 1d6x10 sp.