-3x Despise
+3x Blackmail or +3x Duress

-2x Liliana's Caress
+1x Geth's Verdict
+1x Gatekeeper of Malakir

I will definitely replace the Despise with Blackmail when I acquire them. As for the removal I also agree that more is needed but I am unsure on the numbers of Geth's Verdict and Gatekeeper of Malakir to play. I will also probably bring in some of the stuff from the sideboard into the main

From personal experience, I can tell you that Hypnotic Specter outstrips Nyxathid any day of the week. +1 bc I love rack.

I'd cut 1x of Raven's Crime because it's redundant when in the GY.
Maybe you can up your Gatekeeper of Malakir count to 3x. He's good at what he does.
It's a nice build... overall, I kinda like it
Cheers! +1 for Racks

I'm keen to do some testing with Hypnotic Specter in the main board as the discard a card at random could be a blowout. Nyxathid is only really there to side in if we face a fast creature based match up as a blocker. He could also be an alternate win condition against a deck that can remove our rack's with ease.

I can definitely see trying to fit another Gatekeeper of Malakir in somewhere as well because he has won me super grindy games where i just couldn't find a rack but could control the opponents board. I would probably remove one of the utility spells to fit him in and not Raven's Crime as it's just such a good card in your opening hand even though later ones are not as great.

I agree with putting Hypnotic Specter, but no more than 3x for this build, as you already have other creatures. I still think that you should cut 1x Raven's Crime, reducing criminality by a solid 25%. No, seriously... 4 is too much, I talk from experience on this one: Thiopental (Brigdeless 7-Rack Quandary).
Nyxathid is good, but as you said, only again creature-heavy based decks (not so many nowadays).

Oh, and I just saw you have 4x Necrogen Mists... that might be too many, considering that they are redundant if you get more than one because they are redundant.

I'm in a good mood, sorry for the bad jokes. Cheers!