Unable to speak, and no longer breathing, Brian shuddered as he shrank while more fluid pump out of what had been his mouth. Teeth were gone, along with his tongue, yet he could 'taste' the liquid spewing out. It occurred to him that there was only one place all this piss could come from - his former human body was liquifying.
Dar let go, and Brian flopped helpless down, almost touching the ground. Vision was fading, and he had a last view of Mike mounting yet another mare as the world went dark and silent. But not completely gone. The sensations of his foreskin wrapper, the pulse of blood through his veins, and the continuing gush of urine became intense. He could taste the pee, aware of the heat and saltiness of the liquid, and feel testicles strain as they prepared a very different and thicker substance.
Urination ended but he was getting stiff, filling with Dar's blood as he hardened. Brian felt hot, felt need, felt pleasure, and then shuddered as stallion's cum shot from what had been his mouth. The intense orgasm took away all thought for a while, and when Brian was aware again, he could feel the comfortable pressure of Dar's loincloth holding his mass against Dar's crotch.
Awareness faded in and out, a kind of sleep overtaking the former elf much of the time, but when Brian was 'awake' he found he really enjoys his new position. Sex, both masturbation and with partners, was intense, and urination had a different kind of satisfaction with it. This went on for a while, perhaps months, perhaps years, and Brian barely remembered any other existence. Then he found a new sort of awareness, once that was dim at first, but got steadily stronger. A heartbeat outside his body still sent blood through his veins, but it seemed very different. New muscles formed, and he was aware of limbs for the first time since he'd been absorbed.
As he continued to develop, Brian realized he was an unborn embryo, developing in a womb. But as what? Dar could easily father a foal, or he may have impregnated a human female. Given the stableboy's magical capabilities, Brian's mother could just as easily be a cow, a dragon, or a goat. He was too tightly constrained by the womb to tell anything. He'd have to find out what he was after he was born.