Clone Transformation, an advanced course in Transfiguration, was normally closed to students in the lower years, because its prerequisite was mastery of Transfiguration.
Even among fourth-year students, very few could master magic this advanced.
Zheng Qing had learned Transfiguration entirely by accident.
When he first enrolled as a freshman, the headaches that had lain dormant for over a decade returned. The School Hospital and the school's senior professors examined him at length without finding the cause. In the end, they resorted to the simplest, most heavy-handed solution: teaching Zheng Qing the spell wizards used to evade calamity—Transfiguration.
To use a rather poor analogy, someone had a sore foot, and the doctor's eventual prescription was to replace it with a healthy one. The reasoning might have been wrong, but the result did indeed cure the pain.
In short, through a series of accidents, Zheng Qing began learning Transfiguration.
At first, he needed the aid of a magic potion to perform Transfiguration. Each transformation consumed a vial of Transformation Potion, which was extremely expensive. Old Yao had once reassured Zheng Qing that the cost of his transformations had already been covered by the health insurance for publicly funded students. But from the discreet inquiries Zheng Qing made afterward, the school's other publicly funded students did not seem to enjoy such generous coverage.
Of course, the other publicly funded students did not seem to have suffered headaches that the School Hospital could not treat, either.
As he transformed more often, Zheng Qing's understanding of Transfiguration deepened. Gradually, he no longer needed to actually drink the Transformation Potion to transform. Later still, he could successfully transform simply by looking at the Transformation Potion, or thinking about it. Put more simply, he had mastered Transfiguration through "muscle memory."
He knew how it worked, but not