Mika began running the brush over the centaur's equine back. Where the bath had made the horse hide glossy, the magic bristles lengthened and darkened fur so that the normally mix of white and brown undercoat also turned midnight black. The centaur was watching, obviously fascinated. "I don't have enough gold to reward you for this, boy."
As the grooming continued, Mike saw the already powerful draft horse body get larger and more muscled, yet show indications of increased youth as well. He was sleeker, shifting on his hooves with energy. The effect was reflected in the centaur's human parts as well, dropping him to his early twenties. It was not all positive, though. He could see the handsome youth's features getting coarser, teeth getting larger.
Despite Robin's instructions, Mika stopped grooming when the centaur's equine portion was fully transformed. He did not want this nice person to be tricked into becoming a beast. As it was, the centaur had very become very homely - not obviously equine in the face, but it took no imagination to see the protruding jaw and wide nose as the beginnings of a muzzle. It was so tempting to keep going! So little work left to make the centaur into a magnificent Shire stallion. He raised the brush partway, then made himself drop it back to his side.
The centaur grinned as he twisted this way and that to inspect himself, the obvious delight fitting his teenage face well. "This is amazing! You have made me younger and stronger." Then he stopped and looked at Mika with a chuckle. "So, have you decided if you are going to finish me up into a draft horse or not, the way your master ordered you to?"
Mike started to protest, but the centaur smiled. "Centaurs have excellent hearing. So, what now?"