A couple suggestions,
I would get rid of Diregraf Ghoul granted your getting a 2/2 for cmc 1, but it enters the battlefield tapped and doesn't provide any benefit to the deck beyond the fact that it's a 2/2. Replace it with Vengeful Dead it has a cmc 4 but you're really killing 2 birds with 1 stone. You're getting rid of a low utility creature and replacing it with a high utility creature, and you're getting a Blood Artist style card. It's not a bad trade of as far as cmc goes either, you've got 12 other creatures with cmc 1.
Another suggestion would be to replace 1 Dark Ritual and 2 Swamps with Cabal Coffers. Better utility than Dark Ritual since it can be used repeatedly. As well as doubling your mana output for repeated sacrificing of Gravecrawler
I wouldn't replace Unmake with Hero's Downfall they have the same cmc however Unmake bypasses idestructable, and regenerate.
I would however replace Unmake with Grave Pact it bypasses indestructible, and regenerate, and stays on the field for repeated uses with a cmc4 versus 3.
What I like about unmake is it can target stuff, unless I get the deck to go fast enough to cause the sacrifice of all their creatures. What I liked about downfall is it can take out plainswalkers as well. But you have a point about the regen and indestructable.
Good idea about cabal coffers, but I don't know about using vengefull dead, he seems just so bad, and he and gravepact might slow the deck down alot.
If you're going to run Carrion Feeder + Gravecrawler, you might as well run some other cards that will actually take advantage of that interaction (e.g., Grave Pact, Vengeful Dead or Noxious Ghoul). Otherwise, the deck ends up being a bit one-dimensional. If anything, Undead Warchief seems unnecessary, because you aren't really benefitting much from the cost reduction with the current decklist.
4 carrion feeder
4 death baron
4 undead warchief
4 diregraf ghoul
4 festering goblin
4 gravecrawler
4 dark ritual
4 tragic slip
I was thinking of hero's downfall and blood artist instead of unmake and undead warchief.
I would get rid of Diregraf Ghoul granted your getting a 2/2 for cmc 1, but it enters the battlefield tapped and doesn't provide any benefit to the deck beyond the fact that it's a 2/2. Replace it with Vengeful Dead it has a cmc 4 but you're really killing 2 birds with 1 stone. You're getting rid of a low utility creature and replacing it with a high utility creature, and you're getting a Blood Artist style card. It's not a bad trade of as far as cmc goes either, you've got 12 other creatures with cmc 1.
Another suggestion would be to replace 1 Dark Ritual and 2 Swamps with Cabal Coffers. Better utility than Dark Ritual since it can be used repeatedly. As well as doubling your mana output for repeated sacrificing of Gravecrawler
I wouldn't replace Unmake with Hero's Downfall they have the same cmc however Unmake bypasses idestructable, and regenerate.
I would however replace Unmake with Grave Pact it bypasses indestructible, and regenerate, and stays on the field for repeated uses with a cmc4 versus 3.
Good idea about cabal coffers, but I don't know about using vengefull dead, he seems just so bad, and he and gravepact might slow the deck down alot.
Nameless Inversion and Fleshbag Marauder are also decent, recurring removal options. If you cut some of the weaker 1-drops, you might as well run some number of Leechridden Swamps, because "why not?"
Lastly--obligatory Gray Merchant of Asphodel recommendation.
4 carrion feeder
4 death baron
4 diregraf ghoul
4 festering goblin
4 gravecrawler
4 dark ritual
4 tragic slip
4 grave pact
2 cabal coffers
1 Nykthos, Shrine to Nyx