Nocturne is the name given by the Templars to the monsters they hunt. Their origins are unclear, as is their true nature. They seem to exhibit characteristics both natural and supernatural, and they seem to have existed alongside humanity for as long as we’ve been here.
There are several breeds of Nocturnes, each with different strengths and weaknesses. They all seem to possess some degree of enhanced strength and most have some kind of enhanced resiliency or regenerative ability. On the other hand, they all seem vulnerable to decapitation and silver. Consecrated items and holy relics also increase the effectiveness of whatever weapon/shield/armor one uses.