Transgress the Mind out of the sideboard should help against Bant. Lets you take
Collected Company or a
Spell Queller.
Defeat also kills
Spell Queller and
Reflector Mage, but since you're in mono black,
Grasp of Darkness is pretty much strictly better (maybe swap 2
murder for 2 Grasp since its 1 mana cheaper, and keep the extras in the sideboard).
Infinite Obliterations seems decent from the sideboard as well, naming whatever gives you the biggest problem (Queller,
Reflector Mage, Ulamog).
It's sad, because in pretty much any other standard, Vampires would be really good, but with Bant Company around it really limits the number of playable decks. If you want to compete, you have to be able to compete with Bant, which means being ready to stop
Reflector Mage,
Spell Queller and Slyvan Advocate. Removal hits all these, and
Transgress the Mind hits CoCo. This is why Black Control is doing okay still, because it's able to hit all the key cards of Bant.
Since the vampire deck is more aggressive, you'll have to adapt to give it some of the benefits of Black Control.
Voldaren Pariah seems like the best place to start, since flipping it "should" clear your opponents board and leave you with a 6/5 flyer. However, as Frimmel mentioned, with
Reflector Mage it makes it a challenge to flip.
Maybe run a playset of
Call the Bloodline? Since pretty much all your creatures have madness, you can still fill your board, and when a
Pariah does land, you can just sac tokens for it. Something to think about.
Hope you found this helpful! Good luck and Happy Hunting