Ao Yin is an ancient being, born in the netherworld (阴间 yīn jiān), and is one of the ten fearsest beasts in Chinese mythology (十大凶兽 shí dàxiōng shòu) - said to be on par with Qiong Qi (穷奇 qióng qí).
Ao Yin feasts on living creatures and has a particular appetite for human flesh. He is shaped like a bull, has four horns and a long coat that closely resembles a coir raincoat.
It is said that Ao Yin enjoyed wreaking havoc in our world (阳间 yáng jiān) so much that powerful ancients (unclear which ones) had to banish Ao Yin to Peng Lai Xian Island (蓬莱仙岛 péng lái xiān dǎo) using magic to imprison him in a space he is unable to leave.