As Ken bean to change back, he noticed that the prime stud was over by his clothing, and a cold hand clutched at his gut. The medallion! Being unable to wear it as a horse, he had taken it off with his clothes and left it on top of the pile! He stumbed on still-changing legs, shouting to chase the animal away. But it was too late, he saw the glint of sunlight on the medallion as the boy/horse grabbed it in his teeth and galloped to the far side of the pasture.
He chased after it, hoping that the boy/horse wouldn't figure out how to use it. But he had boasted and tormented the boys after he changed back, and before he got close the stallion suddenly shrank and changed into a familiar-looking human. It was the other kid, though he seemed to have made a few improvments. He was more muscular, handsomer, and obviously still rather horselike between the legs. The boy glared at Ken as he got closer, and then concentrated a moment.
Ken's muscles suddenly locked up - he was frozen in mid-step, unable to move, and fell forward to land face-first in a fresh pile of horse manure. He heard the boy laugh, and then the pounding of hooves as the horse who had the first boy as his penis galloped over. When Ken was finally able to move again, he sat up and wiped the horse shit from his face and saw both of the boys restored and looking at him with very satisfied smirks.
The horse had a normal dick and balls now, apparently courtesy of the boys. Ken was releived that they weren't making him go back there, and suddenly felt terrible about what he had done. "Look, I'm really sorry. I don't know what I was doing - you guys never did anything bad to me. I think it was the medallion! Please don't make me a horse's dick again!"
The boy with the medallion sneered at him. "You were gonna leave us stuck. But being a horse's dick is too good for you. That horse shit looks pretty natural. Let's make it permanent."
Ken started to scream as he suddenly felt himself reform, but the sound emerged as a fart. There was a thick, dark mass in front of him, with coarse hair blocking his vision most of the time. When it lifted, he could see the pasture beyond, and hills of furry flesh on either side.
His body seemed to pulse from the feet up, but it wasn't the sexual throbbing of being a penis. Something thick and heavy squeezed up, and erupted from his mouth. The stink and taste left no doubt. He had been turned into a horse's asshole!
He could hear the two boys laughing. "That will teach the creep to pick on kids!"