What is the headless hound?

Answer 1

A headless hound appears to be a large black dog, but with an eerie green glow where the head should be. The creature's flanks may be lined with scars or torn open, exposing faintly glowing bones and the absence of innards. The headless hound attacks with a ghostly bite that passes straight through clothing and armor to the flesh. The defender's armor class is modified only by any Dexterity bonus. Bitten flesh heals at half normal rate unless magic is used. If five or more headless hounds are present, their howling requires a saving throw to avoid fleeing in fear (only required once). The headless hound takes half damage from normal weapons. Despite their spectral nature, headless hounds are not undead. However, they are immune to sleep, charm, and hold spells. They are more properly faerie-kin, and according to folklore will cease their haunting and join the wild hunt if it passes nearby. Anyone slain by a headless hound has a chance of returning from the grave as a shadow-like spirit, to be pursued nightly by the headless hound pack.