Po: [Tai Lung] was a student, the first ever to master the thousand...scrolls of...kung fu...and then he turned bad...and now he's in jail.
Tigress: He wasn't just a student. Shifu found him as a cub and raised him as his son. And when the boy showed talents in kung-fu, Shifu trained him. He believed in him, he told him he was destined for greatness. It was never enough for Tai Lung. He wanted the Dragon Scroll, but Oogway saw darkness in his heart and refused. Outraged, Tai Lung laid waste to the valley. He tried to take the scroll by force and Shifu tried to destroy what he created...but how could he?
"[Sunset Shimmer] was one of my most ambitious students, but when she did not get what she wanted as quickly as she liked, she turned cruel and dishonest."
—Princess Celestia, My Little Pony Equestria Girls