Bone of Impurity

The Bone of Impurity is a curse native to the Northern Barbarians. It's cast on Chang Geng by Xiu Niang. "'The Bone of Impurity is unparalleled; no one can detect it; no one can cure it.... One day, you will grow into the world's most powerful warrior and begin to be unable to distinguish between nightmares and reality.... You will become a ruthless madman-'"

Symptoms
The long term effects of this curse is intended to drive its victim insane by blurring the lines between dreams and reality. As the victim of the curse is "blessed" with superhuman intelligence and strength, the victim is expected to be able to attain a lot of power or authority. Upon going insane, the victim should then be able to cause a lot of harm.

The victim will experience bouts of attacks by the curse whenever his mind is not stable. These attacks can last many hours at a time and bring about indescribable pain. During an attack, the victim's pupils will separate and others will be able to see dual pupils in each of the victim's eyes.

The curse is usually cast by someone whose country is broken, and the nation can no longer be preserved. Such a cruel curse and method would be used as a sacrifice to the evil gods in exchange for vengeance.