Volrath's Stronghold could be useful, as well as Cavern of Souls , since it helps you place your commander.

A generic Sac engine (Such as Viscera Seer or Bloodthrone Vampire ) can be good if someone wants to Oblivion Ring your creatures. Also, Cauldron of Souls is useful if you want to sacrifice your things twice (Persist/Undying negating each other), allowing them to comeback and, if you have a Grave Pact effect, you can sac your stuff and have basically no consequences over and over. Braids, Cabal Minion can be annoying for your opponents, forcing them to sacrifice stuff, in the same way that Smokestack does (Note: Permanents). Puppeteer Clique can be cool (infinite loop with Mikaeus (wink wink)) and allows you to revive big stuff from an opponent's graveyard, have their ETB effects and, if you choose, you can exile them, wich is nice, it's kinda like Nezumi Graverobber with more shenanigans

Crawlspace can be replaced (In my opinion) if you can manage for your opponents to have no creatures.

Murder would do a better work than Hero's Demise , since you can kill anything with it.

If you're playing multi-player, cards like Contamination will turn the table against you and you'll get beat into oblivion just for playing it.

Finally, Victimize is an awesome card that lets you place fat stuff in play by sacrificing a small creature and do lots of stuff.

Overall, it's a nice deck, even though, in my experience, mono-black tends to be a bit repetitive.

A few cards that may help your deck's control strategy are Smokestack , Karn Liberated and Ogre Slumlord . Smokestack punishes opponents for not playing creatures and opens up the possibility of getting your opponents to sac their enchantments and artifacts. Karn Liberated also gives you a way to eliminate artifacts or enchantments. Ogre Slumlord 's ability triggers whenever a non-token creature dies, so as your opponents are forced to sacrifice their creatures you get to build up a buffer of rat tokens to save your other creatures from Kuon's Essence.