After a minute or so of standing around naked in front of the witch, he was starting to think the whole thing was a trick, and he'd just embarrassed himself in front of a commoner for no benefit. Then a dull pressure in his forehead, which he had been thinking was just a nervous headache, started turned into a heaviness as though he had put on some kind of headdress. The witch gasped in excitement, and Damon crossed his eyes and reached up his hands to find the three-foot-long pole that was poking out from his hairline. He gripped the smooth, hard material in both hands, unable to reach all the way to the pointed tip.
"I... I... I'm really changing!" he said with surprise in his voice.
The witch cackled, "What, were you starting to underestimate my potions? That's one mighty horn you've got there!"
A sudden wave of magic washed over his crotch and then his limbs jerked and flailed in bliss. The pleasure was as powerful as an orgasm but somehow different. His lungs heaved as he looked down and saw that his manhood was shrinking! Finally it withered away entirely leaving a single hole which merged with his anus. Damon screamed!
"What happened to my... my... ?"
"Damon, come on now, you've read the storybooks," said the witch. "Even peasants know that unicorns can only stand virgins. If the energy of sex is so repulsive to them, how could they ever have it themselves? They have no genitalia and reproduce only through magic."
Dan patted his hands all the way around his nether regions, finding that sure enough there was nothing there. No sexual feeling down there at all. In fact, he was starting to ache under a lightly painful aura emanating from the witch. He realized that he was now able to sense that she was not a virgin, and he that when this was over he would have to leave.
Before he could think anymore about this, Damon winced and groaned as new flesh and bone blossomed out of his spine and fluffed out with hair. He felt unfamiliar muscles twitching and looked back to see his tail.
It wasn't like when his horn grew in. His horn was like a big rock sitting up on his skull. This new part actually felt alive! It was covered with short white fur for the foot and a half, then the rest of it was bushy like a horse's tail. He waved it around in circles just to feel it move. He was about to reach out and grab it when he noticed something was wrong with his hands.
They weren't hands anymore! They'd stretched out into long forelegs ending in a couple of toes. His fingernails had turned black and were growing out into cloven hooves. His ankles lurched and forced him up on tip-toes. Damon toppled over and found himself on all fours. He looked back and saw his back hooves finish forming.
The back of Dan's long digitigrade feet started to grow out long mop-like hairs, and the same thing happened to his forearms. Even the top of his head and the back of his neck started as his mane grew in. Then everything else got covered up in short white fur. Finally, his face gave way and erupted into a bone and skin. His new muzzle pushed his eyes apart, and he saw almost all the cottage around him without needing to turn his head. His ears poked up into points, and the change was complete.
"Congratulations, new unicorn. Now run to the woods and be free!"