I would drop the 1-offs of the cards to summon spirit of the night. The chances of drawing all three in a 60 card deck are slim to none unless the game goes for a long time.
I do like the sorceress queen and krovikan vampire combo, but I would drop the sengir, black knights and norritts. They just seem like weak cards in general.
Other cards include pox or smallpox to start acting like you are the strange black creature which feeds on everything cards/life/etc. The Syphon soul helps out with the Shauku, Endbringer loss of life that you sustain so you'd be able to stay in the game a little longer.
Spirit of the Night seems like it'd be pretty difficult to cast, even with Dark Ritual. I know you can tutor him out, but I think you'd have a difficult time assembling the combo with only 1 copy of the tutors, and even then you're sacrificing 3 cards to bring one unimpressive (at least in multiplayer terms) fattie into play. Then someone plays Swords to Plowshares and you start to cry.
I'd cut Pit Spawn and Krovican Vampire for the same reasons.
Can you afford 4 x Demigod of Revenge? It would be really good in your deck, and could take the place of the fatties I recommended cutting above.
A copy of Dread would make your opponents think twice about attacking you. His evasion also makes him good at finishing off anyone low on life.
Hunted Horror can be a gamble, but it's also a way to make an ally at the table. You can drop Horror and give the tokens to whomever has the fewest creatures, and he'll probably thank you for it and attack someone else. Meanwhile you have a 7/7 trampler for only BB.
Almost any black deck not running Vampire Nighthawk is a crime in my opinion. The card is just too good. I don't know why everyone loves sengir vamp its not good. I would drop it and as stated 1-2 offs are not going to help your consistency. I would run a minimum of 3 cards you need to draw consistently.