Madame Marissa had an issue with one of her teachers. She had tried to resolve it amicably but she could not and that is why she had to do what she had to do. She had to turn him into a human pony and that is what she did to the guy. He was shocked and he was humiliated by what she did but there was nothing he could do about it. He had to change.
Madame Marissa and her friend wanted to teach this guy a lesson no one had taught him up until then. He was turned into a human pony and it was a very painful affair for him. He cried and begged the mistresses to stop what they were doing but they did not. They nearly broke his back as they rode on it and whipped him when he did not act the way they wanted.