InvisibleField101

I feel like a lot of the deck floats around 4 mana. Usually means that one piece of the combo has to survive a turn before I can cast the 2nd piece. Not sure how to go about accelerating my mana whether it be mana rocks or splashing green for birds

Ok there are some good synergies here that I like. Xathrid and artist are great and I like the idea of thrummingstone. Needs more apostles tho

That being said there are some definite changes I'd make to make the deck both more functional and easier on your wallet.
Take out everything that's white! Go black/green instead. Take out athreos, thrummingstone, enlightened tutor, and grimoire of the dead. I'd also recommend a different set of demons. Keep grisel and ditch the rest. Add 2-3 Rune-scarred Demon, and maybe 2 Demon of deaths gate since you don't HAVE to have 6 apostles to play him. Lastly maybe 1 Lord of the Void since he's a damn beast against AGGRO decks.

To replace thrummingstone and immortal servitude I recommend a playset of Bloodbond March. It's less mana than thrumm and will combo off faster. Bloodbond March also makes Xathrid less necessary so is drop him for 2 more blood artists.

Thinking the Deck should look like this

24x Shadowborn Apostle
4x Blood Artist
1x Lord of the Void
3x Rune- Scarred Demon
1x Griselbrand
2x Demon of Death's Gate
4x Bloodbomd March
1x Lightning coils
4x Evolving Wilds
4x Terramorphic Expanse
8x Swamp
4x Forest

Deck needs discard methinks. Duress, inquisition of kozilek, or thoughtseize would be nice for turn one but I think wrench mind is a pretty good idea too

Since you don't have creatures, why not use black suns zenith, damnation, anger of the gods to give you more range on your spells?

Your mana base is out of whack. You're running three colors with Just 4 land grab effects and only 20 lands?! The deck is far too dependent on top decking the proper mana you need. You probably want to add some terramorphic expanse or evolving wilds if you don't plan on running more grabs. Your mana curve is relatively small so I'd suggest hovering around 23 lands.

Also I would recommend Awakening Zone since it provides blockers/mana/sacrifice triggers and has great synergy with blood artist. If you do decide to run awakened get zone you might consider dragon appeasement. If you have enchants that make tokens every turn its very effect draw advantage late game.

You might wish to consider Sakura tribe elder over Emissary since you can crack it at instant speed. People tend to ignore emissary in my experience.

Priveledged Position doesn't protect your deck from its biggest threat (day of judgement/pyroclasm effects) on top of costing 3 green it's unlikely to see play until late game if at all.. You should focus constantly dropping out devour/sacrifice fodder instead of trying to protect it. Replace it with some goblin assault which is just like rabblemaster but pyroclasm won't get rid of it.

You already have good token generation but those tokens are just going to sit there til your fatties can devour them. Add Beastmasters ascension to give them a huge boost.

I think you should go down to 2 bombardments. Your devour critters are your largest source of damage and your fodder should be saved for them whenever possible. Also multiple copies of bombard are redundant.

Hope This helps