This deck actually seems pretty sweet. Maybe try a couple of Gray Merchant of Asphodel s. That card is actually pretty sweet.
Daaaamn pretttttyyyyy! For acceleration, DEFINITELY ADD AS MANY Dark Ritual as possible. Wait, that's not legal in modern. Nevermind.
Almost might want another whip. Looks really solid though. I maybe would considering dropping to 2 Griselbrand s. And I honestly think that 23 land is too many. My mono black (granted, it caps at 4 mana) runs only 18, and especially with your Nythkos and Whip, things are easy enough to play, getting up to 4 mana (all you'll really need) will be really easy. If your plan works out, you'd also only need 1 hit with an Umbra Stalker to win the game. Might wanna drop him down to 3.
Solid as HELL though. Might have to consider making something like this. +1 for sure!
I could not get past the Bloodghast he works wonders against mill. I put him in the yard and a land brought two of them out next turn. Damnit.. well done here.
In my opinion, you should use some draw spells and the best for monoblack decks is Sign in Blood . Also since you discard all your hand at once, it wont be a bad idea to have a reanimator spell, i suggest Footsteps of the Goryo , it doesn't work with all your creatures but is awesome with Griselbrand and Geralf's Messenger +1
B.F.M. (Big Furry Monster) is a must have in this deck
I hadn't realized Nantuko Husk was modern. I just looked and it was reprinted in both 9th and 10 edition.