The Dark Knight (name unofficial) is a very powerful enemy fought in the Dusk Tower. It has a counterpart, the Light Knight, that is fought in the Dawn Tower. It can use its weapon for close range, but it is more likely to throw it at you. It acts like a boomerang.
It is best to grapple this knight with your Oraclos Chain if you are going to attack it with your main weapon, for you will not come out unscathed if you run in and simply attack. Grappling its wings causes it to fall to the ground, making it easier to attack.