Of course, even the best mage had problems in the art and the former princess was no better. After the decision to change her various royal guest that trespassed in her forest she encountered the first hurdle, namely the limitation of transformation magic, as this branch of the art was difficult to master, and the main issue was that the transformations were not permanent.
She could change a man into any kind of animal, the more unaltered the body mass between the two forms the easier it was, but the curse could last days, and a week was already pushing for all that it was worth.
This was unacceptable, because all her hard work would be undone naturally after a short while. That was when inspiration stuck her: she read extensively about duels between mages, more often than not incurring in a bid to steal the research of the other practitioner, and in one instance recorded the wizard attacked changed his body to that of a pike fish, and hid into a nearby lake until the other magic user left, after he couldn’t find him.
That spell should have been impossible, because she remembered that the invading man was very stubborn, and seized the home for nearly three weeks! The besieged mage probably could not refresh the spell fearing the detection of the magic usage, so this could be the answer to this riddle. What could be the reason for the extended duration?
After a few hours of research the witch was pretty sure of her answer, and it was obvious in retrospect: the key aspect was the desire and will of the cursed. A man didn’t desire to be an animal for long, so their willpower actively fought the spell, draining and neutralizing its effect.
Following the new line of research the sorceress, after months of experiments, was able to finally craft her masterpiece, a spell that could permanently alter the body of the subject at will. The curse was not without drawbacks though, and could only be used when the recipient was willing to change in the form of an animal, keeping their minds completely intact in the process. This is where the deviousness of the witch began to show, because the spell recognized the desire of the afflicted to be a beast and tricked, for lack of a better term, the body into recognizing the old form as the transformation and the new form as the rightful one.
The own body of her victim would fight against a return to humanity, even with outside magical help, and she was the only one able to reverse it, being the creator. This way even if the princes regretted ever becoming animals in the future their willpower will keep them as they are.
The next step was to kidnap some royal, and trick or persuade the inevitable gullible prince with dreams of glory into dropping on all four all on his own…