This is definitely a very powerful creature deck. I would first recommend more dredge, which would drop creatures into your graveyard. The Shambling Shell is great for that. I would follow that up by adding more ways to pull creature back from the graveyard. Rise from the Grave is good as it can also pull a creature from an opponent's graveyard too. Bone Splinters is a good removal spell for this kind of deck. You sac someone who you've already used, such as the Eternal Witness or Acidic Slime to get rid of one of their annoying creatures, then you bring back your sacrifice to trigger its effect again. Since it looks like you want creatures in the graveyard I would also recommend Boneyard Wurm , Splinterfright , and Svogthos, the Restless Tomb as they all get stronger with creatures in the graveyard. Golgari Germination is nice with creature sac as you get 1/1 saprolings each time. Death's Presence could help you power up creatures as you sac others. Reveillark could be nice earlier on. You use it too bring back the Yavimaya Elder or other creatures that help you build up a mana base after you sac them. As a possible near end game you could try Living Death clearing your opponent's field and filling your own before you rush them the next turn. Finally as a win con you could have Mortal Combat since you are already making heavy use of your graveyard and benefit from having creatures in there or putting them there.I hope my suggestions are useful. Your deck does seem like it could be a difficult one to fight as everything keeps coming back for more. Beware the Undead Alchemist though, it could be a major problem for self mill.

Thanks for the comment! This deck is super fun to play. I'm glad you like it :)

Since this is a control deck, I'm not really looking for aggressive cards like Boneyard Wurm , Shambling Shell , and Death's Presence . Splinterfright could be interesting, but he's pretty easy to remove. I'll try him out in a few games for sure.
Reveillark is a good idea. I'll proxy one and see how it goes.
Living Death is definitely something I want to add. Twilight's Call is filling the slot until I can get my hands on one.
Bone Splinters , Rise from the Grave , and Golgari Germination are small potatoes. Not worth cutting anything to fit them in.
Mortal Combat would be fun to pull off but it's not very practical. I'd have to mill over half my creatures to win lol

MORE DREDGE!

Golgari Thug

Golgari Grave-Troll

Also Dread Return, Treasured Find, Living Death, and Entomb

What do you think I should cut?

Hmmm, maybe less sweepers? Because I think you want cards that only fill your graveyard that way when you play a card like Living Death You get the most out of it and your opponent gains little to nothing

Yosei, the Morning Star ends games, when paired with Saffi or Nim Deathmantle. It also works with the Karmic guide combo.

As for cuts you probably don't need 38 lands. I wouldn't go below 36 though.