First of all I am +1ing you for running Kalitas. I never see him run anywhere. As strong a card as he is, he is also VERY mana intensive. Getting to cast him even once will be a challenge with the deck the way it is now. You need more mana sources.

Things like Sol Ring , Everflowing Chalice , and Phyrexian Totem ... or things that help your mana like Caged Sun and Gauntlet of Power or Extraplanar Lens . At least then you would have a better chance of seeing him get into play and potentially being able to cast him again.

Also some ways to protect him/give him haste would be helpful. Swiftfoot Boots , Lightning Greaves are EDH Staples for this but any equipment offering haste or hexproof/shroud would be great.

And Skeletal Vampire is one of my favs :)

Liliana of the Dark Realms is good in EDH, espically when you want to combine it with Nirkana Revenant to boost her to massive levels of power. If you run Urborg, Tomb of Yawgmoth you can also run lands like Strip Mine and they will still be swamps on the battlefield. But not in your library, unfortunatly +1 Upvote

Think about some reanimation such as Reanimate , Animate Dead or Rise of the Dark Realms

Boardwipes too such as Black Sun's Zenith or Damnation might help

It's a mono colored deck so adding a Nykthos, Shrine to Nyx can get you some extra mana when you have a strong board presence

Butcher of Malakir is fine but if you want something more permanent consider Grave Pact . Pair either with Grave Betrayal for lots of fun after a boardwipe

Think about exchanging Nightmare Lash for Lashwrithe or Strata Scythe . Scythe gives you more power because it counts all swamps on the field, not just yours. Lash gives you an option to equip for mana or life and comes with a creature you can swing with if you have no one to equip it to. Also, if you're running vampires, Blade of the Bloodchief is kinda a must

Urza's Incubator might be something to consider. Don't know if you need more kill spells, but I think Go for the Throat and Victim of Night are both good (and both work with the flavor, especially victim). Also for mana, Crypt Ghast is good, and if you have some $$ you can run Extraplanar Lens and Snow-Covered Swamp for every swamp. That way you get doubled mana, but your opponents who run regular swamps won't.

@markbeloit I don't run Victim of Night because I mainly play this deck with my father who runs a zombie tribal deck, but thank you for Urza's Incubator .

I too have a vamp deck Commander Tell me what you think. +1 from me

I'd say throw in an Adaptive Automaton , but other than that, nice tribal!

I could offer a decent amount of card draw options, but at the least, Phyrexian Arena

You should play Dark Depths just because you're playing Vampire Hexmage just so you have the possibility of the god opening of turn 1 Dark Depths pass turn 2 Swamp into Dark Ritual into Vampire Hexmage sacrifice it to remove all counters from Dark Depths and then put a 20/20, indestructible and flying token into play :) fun right. Other than that it looks like a really fun deck +1.

Oh and if you're playing against decks that warrant a spot for a card like cremate you should just play Bojuka Bog or Grafdigger's Cage or even Tormod's Crypt instead they're better imo.

Considering that your running 31 vamps how about running lots of creature ramp card that buff them up

I would say to change your swamps to Snow-Covered Swamp just in case you fight people who run Extraplanar Lens since most people who run that card also run snow-covered lands.