I started thinking about reave and how the mechanic interacts with blue. The reave kicker mechanic will not itself appear in blue. However, blue at all rarities is able to interact with the graveyard, particularly where instants and sorceries and sometimes even artifacts are concerned. At common it can return them from the graveyard (expensively). At higher rarities it can exile and play them. So there is some good mechanical overlap between blue and black and reave that's can be combined to encourage a style of deck where you're rewarded when sorceries or instants leave your graveyard. A couple of commons that can help set things up:
I made the trigger here a sacrifice to present the cephalids as a dark and desperate race.
And the new signpost uncommon:
So both of the above cards can trigger Blightcoast Reaver's additional ability. Oh, I just now realized he has "Reaver" in his name but he doesn't actually have reave. I'll have to rename him.
I'm probably going to do some more iterating of Xirn, too. I essentially gave him the same ultimate as Jaya in order to make the old U/B dynamic work. What I need to do is give him a graveyard exile engine as his + power to help this concept.