(Ha, good old Chinese folklore, handling the X requirement easily!)
They leave disease and putrid swamp in their wake.
A Xiang Yao is a spirit with nine horrid heads on a large snake’s body. They bring disease and sickness, poisoning fresh streams into putrid swamps. They serve the great black dragon Gong-Gong, bringer of the great floods. It’s best to stay far away – an encounter is likely to leave you sick and weak.
Image taken from the Mythical Archive