I need help with my blue black infect deck?

I would consider adding the new black discard card, Distress. Phyrexian Obliterator might be a good addition too. I would remove Lilliana Vess entirely, she is just too slow in this deck and is rotating out soon as M12 is not reprinting her. You might want to run Sword of Feast and Famine or Sword of Body and Mind which will give you some more damage with Phyrexian Crusader.