Hollow Men

Striking a similarity between zombies and skeletons, they tend to have varying sizes, but always humanoid.
Hollow Men are ancient corpses animated by the restless souls of the dead (also called 'Wisps', see wisps for more info.)
They often attack in large groups and waves, showing a form of intelligence and battle strategy, the purpose of this is unknown.
Hollow men are EXTREMLY flammable, due to their extremely dry and dusty bodies.
Somehow, despite being completely dry dead husks of ancient people, they somehow bleed.
This blood origin has never been explained.