There are enough differences though, it's definitely NOT just a reversed and recolored image.
and
however... XD
What makes it even more interesting is that Duskbringer and Nevermove are used as a gapclosing potential. Nocturne can chase enemies hit by his shadow trail and Swain can drag people to him.

Nocturne is a demon. Riot calls it his demonic hand.
Makes sense.
That was my first reaction too, nocturne's other hand