I think a sacrifice outlet would be good with all of your resillient threats and "Dying matters" creatures. Something like Nantuko Husk or Bloodthrone Vampire for the beats, or Viscera Seer for the value.

Other cards to think about are:
Bloodsoaked Champion, a much more aggressive version of Reassembling Skeleton.
Geralf's Messenger for similar value. Also aggressive, but he's very annoying for your opponents to deal with.
Vampire Nighthawk is a house if he doesn't eat a Lightning Bolt. Gaining life makes racing more profitable for you, and he does serious work on defense- trading up like a boss.

I also have a modern mono black deck if you'd like to take a look. SLAP THEM WITH YOUR BIG BLACK DECK

Thanks, I was meaning to add nighthawk just too hungover to think this morning. I went reassembling skeleton because bloodartist/deathgreeter not really aggressive enough to suport bloodsoaked champ. Replaced kill spells with ruthless ripper, and add vamp night hawk to add more early aggro, and support bloodsoaked.