Bel

okay, going through these one at a time, it seems like you've alredy figured out most of your cuts but I'm also not a fan of balor, tzaangor shaman, mutalith vortex beast, or blood for the blood god!. dark ritual and scroll rack are also a bit too cute, i'm not sure they're actually going to do what you want, but i'm down on dark ritual outside of specific decks anyway.

as for what to add to make you more resilient, if you want to be a tribal deck i would look at generic tribal cards like kindred discovery to draw cards or patriarch's bidding to get your demons back from the graveyard. you're also a black deck so mass reanimation like living death is also an option.

mass reanimation also wins games but for extra spice you're in the tribe with liliana's contract as a wincon so consider that as well.

Balor's mostly there for extra damage and being a decently costed 5/5 demon. I get wanting to cut Mutalith Vortex Beast since it honestly doesn't do much, but why Tzaangor Shaman, Dark Ritual, and Scroll Rack?

Also, what would your advice be if I want to focus more on the spellslinging aspect of the deck? 

i don't like tzanngor shaman because i don't think your spells are good enough (with spellslinging it's a different story). i don't like balor because it's just so slow to do anything and what it does do is be mildly annoying. i don't like dark ritual because with so many big mana spells you're trying to cast i feel like i'd rather it be a permanent ramp piece like a mana rock and i don't like scroll rack because while i get what you're going for -- casting a spell in your hand off of cascade -- there are only a couple cards that really really want to be cast off cascade and it's not a great card besides that specific instance. as i said before, it's a bit too cute but also edh is about pet cards so go nuts if you want to keep it.

for spellslinging i'm imagining cards like flame rift, volcanic fallout and pestilence doing a lot of work, putting up large amounts of damage for your commander andto turn on big alternate-cost spells like treasure cruise, cave in, and gush.