Luke trotted happily, his broad hooves making loud clacks against the pavement. He was pretty sure he knew who the sponsors were - the famous beer company actually had a large facility in town where they gave tours and showed off thier... Luke's lit up and he changed direction slightly. Some of the hitch horses were kept at the in-town brewery, and he wanted to compare himself to a real stallion.
Although Luke knew there had to be magic involved, he didn't realize the costume picked up on the wearer's desires. Most people just wanted a great costume, and nothing else would have happened if the costume was returned. But Luke not only admired the great Clydesdales, he envied them. And just as the clerk had noticed changed continuing as Luke left the store, the centaur that arrived at the brewery stables was already a lot horsier.
Several Clydesdales were running out in a paddock area with a groom watching over them. Although he had not been expecting an addition, the young man chuckled as he opened the gate to let Luke in. This wasn't his first Halloween. And as for Luke, he had eyes and a nose only for the mares. There was a gelding in the small herd, but he was mostly ignored. Luke was pleased to see he was the largest of the Clydes, though he wasn't sure why. The one of the mares lifted her tail and he forgot all but a powerful need to mate.
If he had any doubts about the costume's completeness, they vanished as his equine cock pushed out. The huge member hung heavy and hard, swinging under his belly as he impatiently worked to line up. Then he surged forward, sliding over the female's rump. It took a couple of prods before he entered her, and then he was lost in instinctive passion. The act was repeated twice more, and by the third mounting a normal-looking stallion was covering a mare.
The groom grinned as the last changes completed, knowing they had another fine young Champion. And Luke, fully sated and no longer remembering ever having been human, pulled up grass with the other horses.