Obviously you have the experience, but I cannot see how you're getting land-flooded with this deck on a consistent bases. With 11 6-7 drops, and other cards like Imposter and Big Drana being so mana hungry, I'd think you'd want to run closer to 36-37 lands. Having more reliable draw (Greed, Erebos, God of the Dead, Arguel's Blood Fast  ^Flip) or just more draw in general (Night's Whisper, Sign in Blood) would help smooth out the games you were drawing lands and help you cast your bigger spells.

Not having that issue anymore. I adjusted lands and added Magus of the Coffers, Phyrexian Arena and Necropotence, and it's running very smoothly now. I'll keep your suggestions in mind in case it gets out of balance again. Thanks!

Definitely worth adding Necropolis Regent and Nirkana Revenant they both just add power to the deck Cabal Coffers is much more durable than magus of the coffers but it’s not an easy thing to get a hold of so definitely worth an add another not so easy thing is Cavern of Souls it just stops blue decks from countering your vampires, things I’d remove for them gifted atherborn it’s not that great in honesty and I’d remove Skeletal Vampire on the basis that it’s a lot of mana when you could have a bigger powerhouse in play like either of those two. Reanimating Wise you could add Patriarch's Bidding I always recommend it for tribal decks and I would still leave Mutilate in as it’s still powerful in a mono black deck Sudden Spoiling can help you get around nasty abilities or big monsters, if equipment is the way you want to go then I’d add Lashwrithe

Feel free to have a look at my deck Drana mtgo it’s more voltron based and list needs updating as I now have a few new adds but feedback would still be appreciated

The first three you listed are on my maybeboard, which I will be getting and putting into the deck eventually. I'd like a Cavern of Souls but they're way too pricey for me right now. You'd be surprised how many times Gifted Aetherborn saved me - everyone's afraid of that little guy. Skeletal Vampire will be removed eventually, but for now he's there as a mana dump late game. Patriarch's Bidding is neat but I run into way too many tribals in my area, so it would be a gamble. I do like Sudden Spoiling but I've ran it in this deck before and it was lackluster for my play style. I definitely want to stay away from being equipment-heavy, but Lashwrithe is amazing in mono-B. Overall great suggestions, but right now I either don't have them or they don't fit my play style. I'll keep them in mind for later.