First and fomoest, Chang(伥) is a kind of Chinese ghost. Some ancient Chinese books describe Chang.
In Tang dynasty, Dai Fu, written a book Guangyiji, to record mysterious, supernatural things.
At chapter Xuanzhouer, he writen,
At the end of TIANBAO(C.E. 742-756) in Tang dynasty. There is a child living near to the mountain, at Xuanzhou. Every night, he always seeing a ghost leading a tiger to cheat himself. This happened more than ten times. The child told parents, “I will die because the ghost was leading a tiger. People are saying,’If someone is eaten by a tiger, then he will become Chang’. I will become Chang, if I died. If that happened, I will lead tiger to village. You can set a trap in the road it must take, and you can catch a tiger”. Several days after, the child died by the tiger. long time after, his father have a dream that the child said, “I have been Chang already. I will lead tiger to village. You can set a trap in the west of the village.” The father set the trap. when the trap was set, a tiger was caught.
In book Beimengsuoyan, which was written by Sunguangxian in Ming dynasty, recorded:
One died by tiger, or drown in water, will become Chang. They must seek someone to replace themselves.
This is a definition of Chang. But later, Chang’s meaning narrowed to a ghost was died by tiger.
The book named Zhengzitong, Tingyujitan, which was written in later years of Ming dynasty, give more detail about Chang:
It was said, that one was eaten by tiger, not dear to go elsewhere but serve for tiger, called Chang. Chang is the guide of tiger. If Chang meets a trap, will find another road. people killed by tiger, with cloth be loose and stripped, is leading by Chang. If there is a person followed by Chang, tiger will eat him.
There is a Chinese idiom, 为虎作伥
为虎作伥 means become Chang and help tiger to kill people. It usually means help a villain do evil.
This is my writing exercise. If you think there are mistakes, please point them out.