Tye decided to hold off. To be honest, he wanted to see how the magic worked here, and he could probably stop things from going to far - if he chose to. Having Mike become a Shire-based centaur wasn't that big a deal, but he knew the stableboy intended to match Mike up to the mare a little more perfectly than Mike might want. He decided to leave it up to Mike, though he would make sure there were no tricks played. If Mike became a horse, it would be because he chose it.
The centaur shivered slightly as Liam continued to pull the brush through his fur. It felt amazing. and the glossy black hide forming over his back looked just like that of the mare beside him. She was really a beautiful animal, and affectionate. Her thick, powerful lips pulled at his side and arm, returning the grooming of his massage. Being so close to the powerful female began to get him aroused, and he felt himself drop. Mike flushed a little, realizing his cock was enormous and hanging down under his belly.
Liam noticed the heavy shaft as it stiffened and chuckled. "Enjoying this?" He stepped down off the bucket and used his free hand to heft and rub Mike's penis through what felt like a foreskin. As he stiffened, the tube of flesh stretched and then slid back to reveal the flared glans. Liam ran the soft bristles of his brush down the length of the shaft, turning the mottled pink and black skin solid black.
Mike's eyes widened and he grunted as the sensations nearly overwhelmed him. Powerful magic throbbed into his testicles and rose up into his belly. It was so weird. He would never have let the boy handle him like this if he'd asked, but now Mike did not want him to stop! His cock arched up, bobbing with each pulse of blood, and he felt pressure building in his loins.
The boy watched Mike's face with a knowing smile. "You are a centaur. There is no reason to feel shame for reacting as a fine stallion. It is your nature." Mike felt his cheeks burn even so, being masturbated like an animal. Was it normal for a centaur to have a stallion's lack of modesty? It did make sense, since they were just as exposed. Mike shuddered as an orgasm built. "I want to accept that, but it's not easy. I'm used to clothes..." He rocked involuntarily as his massive, now-black testicles began to stretch taught. "Oh, man! A stallion! Yeah!" That last was shouted as his huge cock erupted with a blast of cum that splattered Mike's equine chest, forelegs and part of the back wall.
Mike stood panting and wide-eyed as the intense sensations slowly faded. He became aware of Liam brushing him again and grinned. "Bet not too many stallions in here can put out that kind of load." Liam chuckled as he finished up Mike's back. "Wait until I am done. In a few minutes you'll have recharged Shire balls to empty."
"Great!" Mike felt eager now, not even remembering his prior embarrassment. Liam was working on his side, but the magic was beginning to spread on its own. Mike's tail darkened and lengthened, and the glossy black hair eased down his other side as well. It was more than just color - more muscle was forming under the hide, and the centaur shifted as bones lengthened and thickened. Mike's tail lifted, and he took a very horse-like dump without even noticing.
Tye watched the manure fall and grinned. That load of cum had carried Mike's human modesty with it. He doubted if the centaur would notice, much less care, if he took a piss in the middle of a bar. The stableboy had rather effectively made that part of Mike's awareness fully equine.
The transformation was moving quickly now. Mike was obviously taller, and his equine parts were almost fully Shire. Muscles rippled in his human portion now as it became proportionally larger. Mike's brown hair turned black, and his skin began to darken. The centaur was huge, even larger than the female who was now shuffling in an agitated manner. She was in heat and wanted the male very badly.
Mike stared as his arms darkened and bulged. Twisting around, he grinned at the powerful Shire body that was now his. He must weigh more than a ton now, and he felt like he could drag a building off its foundation. The change of skin color was unexpected, but he liked the way his coal-black skin flowed into equally dark horse hide.
Liam stood back as the last physical changes finished up, through Tye could still sense the throbbing of magic. "There you are. Magnificent!"
Tye had to agree - Liam was eye-popping. He appeared to be older, maybe in his early twenties, human portion perfectly matched to the powerful draft stallion below. Mike's featured were coarser now, but still recognizable even sculpted from black flesh. His eyes were larger and looked to be a mix of horse and human, not quite either. The shape was mostly human, but Mike's iris's were those of a horse.
Liam moved to the stall gate and let himself out, carefully closing it to keep Mike and the mare inside. "I think you have some business to attend to."