May want 4 Deadbridge Chants

Golgari Grave-Troll is big and dredges for 6
Darkblast dredges for 3 and does it again
Life from the Loam gets lands back you dont need that is your graveyard

Stinkweed Imp good blocker never dies and dredges 5
Nyx Weaver mills you then gets your win card back

Splinterfright would help you too!

he plays 4 Splinterfright look at the dack

lol my bad XD

BTW its deck not "dack"

Satyr Wayfinder would help you out a lot. Cheap for a good mill-4 and draws you out some land. I'm also a big fan of Nyx Weaver and it would help you out a lot if you put something wrong in the graveyard. Plus spooky spooky spiders!

I was originally running 4 Wayfinders, but I'm currently experimenting with Dawntreader Elks. As for Nyx Weavers, I'll give 'em a go due to popular to demand, plus Spiders seem to be a recurring theme for this deck.

Gurmag Drowner He's awesome. Mills four (counting the sacrifice which can be himself) and he get's you a thing. Totally better than the Armored Skaab or Necromancer's Assistant, don't you think? +1

Good list. Have you considered altering your mana base slightly for Nighthowler in place of a couple of Spider Spawning? It puts even more creatures in your deck and although it doesn't have any helpful keywords like Splinterfright's trample, it counts creatures in your opponent's graveyard too. You can Bestow it on the Aven or Crows for a massive flyer or just have a huuuuuge Splinterfright; plus it'll stick around if that creature dies.

Sideboard looks solid enough. Maybe fill it out with 3 Nighthowler if you aren't maindecking them. +1

For the sideboard, you might also like Caustic Caterpillar instead of naturalize, that way you still get some value out of it in case you mill it. But I definitely agree that nighthowler is the bee's knees.

I know it ain't budget, but I think that Deadbridge Chant and Lord of Extinction will do the trick

Lord of Extinction sounds great, but it's $15. No thanks, for now.

How about Grave Strength?

Revenant could be something to consider as well

Sultai Ascendancy is awesome!

For milling (maybe as a replacement): Gather the Pack

I'd advice to run some form of removal. Murderous Cut would be perfect; you're probably going to mill a ton of lands as well, which you don't really care about, so you can delve them.

Maybe run some sort of grave return (cards like Macabre Waltz and Dutiful Return, maybe even Possessed Skaab or Greenwarden of Murasa).

Sideboarding countermagic is also advised. I'd recommend sideboarding 4x Negate or Rakshasa's Disdain, to prevent you dying to something like Tormod's Crypt, or worse, Hedonist's Trove.

Just bought all the cards needed and this deck is awesome :D

What about Nemesis of Mortals?

@Nasur86 I was thinking about Nemesis of Mortals, but I think it's outclassed by many other creatures in the deck.