Something formerly human. They are unburied bodies under a warlock's spell. They try to grab hold of you while wailing and emitting a horrible odor.
This things may not look tough on their own but they come in large groups with the Green Flyer, they can cause Poison but don't worry Poison does not take away much HP.
The Japanese name for the Zombie, Shiki (屍鬼) is a type of spirit that inhabits corpses. The characters in its name literally mean "Corpse Demon".