Suggestions should fit within the general theme of the deck. Yes, economy is a factor. ie don't tell me to take out a card that has cmc of 2-3 for one that has a cmc of 6-7. That's just silly.
Let's start w/ the creatures:
Nip Gwyllion and Mourning Thrull are good early drops w/ the life gain. Getting two Edge of the Divinity on Nip Gwyllion turn 2 can be quite the frightening prospect. Getting smacked for 7 life gain damage that early on will definitely take you right out of your comfort zone.
Blind Hunter A 2/2 flyer w/ an accompanying 2pt life suck and another 2pts when it haunts something.
Nightsky Mimic Practically all the spells are black and white in this deck, so it's rarely gonna be anything but at least a 4/4 flyer when it swings.
Necrotic Sliver If necessary you can just sink the 6 mana into taking out whatever permanent. Think of it like a black and white Desert Twister in those cases.
Deathbringer Liege Practically everything in this deck is black and white, so almost every spell will trigger a kill. All the creatures are black and white, so they're gonna get the 2/2 buff. SCORE!
Now for the spells:
Edge of the Divinity = Holy Strength and Unholy Strength in one. How can you go wrong w/ that?
Unmake Mortify and Vindicate Gotta have removal in there. Mortify can take care of some of those pesky enchantments, too. Vindicate can take care of ANYTHING.
Batwing Brume A fog w/ pain. Enough said.
Cauldron Haze The most recent of additions to this deck. Helps a lot of the moving parts in this deck. Wanna kill my Deathbringer Liege? Well, now he's got persist and I just killed one of your creatures! HA! Recycle my Necrotic Sliver to kill a 2nd bird w/ that one stone? SURE!
Used to have a couple of Metallic Sliver in here just to get extra use out of the Necrotic Sliver ability but I cut them for another each of Batwing Brume and Cauldron Haze. I think it was a good idea. : /
