Awesome! The sheet is looking sexy. 

And at th moment, i'm still in the process of looking for a picture that properly captures them, but imagine what would happen if you mixed a Predator, a Space Marine and every single 'eldritch' race in sci-fi. They're large humanoids (about 8ft) donning strange armour; flitting in and out of the physical realm with such blinding speed that they appear only as an outline of ethereal smoke at times. They are ferocious, and get in your face so fast that most characters won't have time to react before getting sliced in half. Hence creative tactics. 
But yeah, i'll update you when I find a suitable image.