Dark deal has a bigger, better brother- Delirium Skeins. It crushes combo and control if it resolves, and while it hits your own hand thats usually ok with a waste-not out there. Run both. I'd go with a 4/3 split, as that and waste not are your deck's 'thing'.

Maindeck sangromancer is definitely the right kind of idea, trying to take the edges off of those aggro matchups. That said, its a four drop, and you'll hopefully have already emptied their hand. A bigger ETB is worth looking for, I'd go with Gifted Aetherborn or even Vampire Cutthroat over nighthawk- it costing less mana matters so much when you need it as fast as you can for burn.

Remember that your opponent is likely to have at least some creature removal in all but the most aggressive matchups, so you want creatures that either naturally resist that (hexproof, protection, etbs, etc) or only matter against the aggro matchups that are removal-light, so that you can spend your hand disruption on their threats. Night's Whisper and Sign in Blood will serve you better than asylum visitor.

Shrieking Affliction or Profane Command in place of attempting to finish your opponent off with creatures is a good option, and the other is to cheat creatures out of the graveyard so that they are less valuable. You can do a lot with sac triggers to dodge removal if you stay on the creature plan- an Indulgent Aristocrat and a Call the Bloodline is surprisingly functional if you run stuff like Call to the Netherworld. It effectively blanks a lot of removal, and killing their hand quality by leaving them with dead cards is great.

The idea of t1 disruption, t2 enchant, t3 big discard is solid, play heavily into that. Once the game is stalling out and you're both in topdeck mode, you want to be sure that you maintain the advantage. Ok, so the classic lili plan is out of the window because its stupid expensive, but Ob Nixilis Reignited will be castable most of the time you want it, and with a lot of maindeck discard has basically the same abilities.

Remember, black's main advantage is flexiblity- feel free to grab something out of my big list Mono black deckbuilder's toolbox to find something that hates on your metagame.

Thanks again lagotripha. I definitely agree that skeins needs to be added and I went with Abyssal Persecutor as my sangromancer replacement. I'm concerned that I don't have enough 1 drops though. What should I remove for a couple more of those? Or do I even need them?

This feels a lot more solid now, perhaps a little heavy on the four drops. I think that if you need more early game, drop a couple persecutors- you can probably run shrieking affliction in their place to similar effect.

Two sangromancer or persecutor, a dark deal and another kill spell would probably be my split, but its one of those meta calls- all depends on what you are likely to need to survive.