It was Time. He could smell the female scent on the air, and he snorted at it, despite his age. He had driven off the young bucks this year, through size and cunning, and all the shes here were his. All he had to do was take them. And so, he chased the scent to them.
... This was not right. There was the smell, but no she! And with a hissing sound, something struck his flank, and bellowing in pain and terror, he fled, as fast as his body would carry him, his instincts caring which way he went, only knowing to flee. And he did, past the edge of the forest, and into the place that reeked of blood, unable to smell it for the hot stench of his own. And in short order, he stumbled, and he fell, rolling down the banks into a shallow river, his head mercifully landing above the water, and he slept, too tired to move.
And when he awoke, he drank deeply of the water about him, and again, slept. It was several risings and fallings of the sun later that he staggered to his feet once more, driven by a hunger he knew he could not sate out here. A hunger for food, and a hunger for females. And he strode towards the forest, his six feet thundered in perfect harmony, and his great horns lit the way, despite the dark of the night.
Standing a full seven feet at the shoulder, Donnerwunsch is, or was, an enormous and muscular stag. His pelt is the dark black of a storm-riddled night, streaked by marks of crimson, the brilliant red of fresh blood. His six hooves never actually bring his legs into contact with the ground, each step reverberating with the roll of thunder as he treads with toes of solid sound. His horns are crafted of lightning, sparking and crackling as St Elmo’s fire climbs between them.
Donnerwunsch, despite his size, strength, and excess legs is still, in mind and instinct, a common deer. He is more or less entirely unsuitable as a mount, except for perhaps some very few druids or ranger types. He will fight and flee like one as well.
What is truely special about him, however, is the aura that the blood of the God of Desire has infused him with. All creatures capable of feeling lust or the mating urge that come within several hundred feet of him have that emotion or instinct kindled to its fullest - The desire to rut is overwhelming, enough to give pause even to hardened soldiers, doubly so if appropriately gendered members of the opposite sex are present. The affected have been known to fight each other over choice of mate. As his legend grows, there have been some small villages that have erected shrines to him as a fertility deity!
Why is everyone so ... randy? Donnerwunsch has made his haunt near a town that the PCs are staying in. Can they survive each other, and possibly random dwarven(troll, ogre, whatever) suitors as they seek the cause?
Seeking to save his dying race, an elder of an ancient race (Elves, etc) has heard the legends of Donnerwunsche. He hires the PCs to capture the beast to inspire his fellows to new feats. Alternatively, the richest house-of-illsrepute in the capital is looking for a new mascot.
A crafter seeks the stag’s horns, hooves, or anatomical ahem for a project. The PCs must obtain.