Ok so i just came up with a theory :P Theory: You'll notice in one of the scenes shade's eyes are yellow, but his eyes are supposed to be dark blue. Black diamond happens to have yellow eyes, and she/he apeared at the end of the chapter, giving shade a necklace. So I think that the necklace could be an outlet to get in shade's mind and posses him..? But, in the ravensong prophecy they say "Feather's pure white" and white raven is related to this because she's named after a bird with feathers, and the color white. She also happens to have one of these necklaces... so black diamond could also be trying to posses her aswell I guess
