Hi!
I'm not that experienced with B/W myself, but I do believe this build would struggle for consistency.
The first thing that comes to mind is that you'd probably be better of with a couple of more Lands in your deck. I usually play 26-27 lands in a Control deck, because you really don't want to miss a land-drop in early stages. I can't really see why you'd run
Warped Landscape when you have no need for colorless mana. I think you'd be better of by replacing them with 2 more copies of
Shambling Vent and possibly 1 copy of
Blighted Fen since you might be able to pull the Sacrifice ability as you play a long and controlling game.
For the Planeswalkers, I believe the new Sorin will be a lot better than Ob Nixilis because it can also kill a Planeswalker, which will be quite important in the following Standard format I believe. Maybe try with 2/3 Sorin and 1 Ob Nixilis, might even want to cut the Ob completely because he becomes very vulnerable after you use his killing ability. Think about it, the soonest he'll come into play is turn 5 and if you - him, he'll be pretty easy do deal with for your opponent while he's only at 3. I'd also try to run
Gideon, Ally of Zendikar. I think he'll get very good in the upcoming format because it will be a bit slower from the start so Gideon will be able to see more play and influence games more often.
Drana's Emissary looks a bit too slow for me so I doubt she'd be able to get lots of damage in, and besides, you don't really want to tap your mana in a control deck, you want them to be open for countering your opponent's moves on their turn. Also, it's a very bad draw and/or topdeck in mid-late stages. You'd really want to draw something like Sorin,
Secure the Wastes of even a removal spell at that point. Or even a Gideon if you'd play him. (Which I really think you should because he's a win condition on his own as a 5/5 creature).
I'm not sure which low-cost B or W creature would replace her currently, but I think you don't even need to replace her with creatures. If anything, you should play an
Archangel Avacyn or two because the card will be broken in control decks. It can do a lot of
dirty work for you and is also a efficient attacking outlet if needed.
The removal in your deck is solid I believe. I'd try
squeeze in a
Planar Outburst so you have a board clear option if needed. Two copies of
Languish also seem a bit overboard since it's a Sorcery and it's not that cheap to cast. And you do play 4 copies of
Grasp of Darkness so I believe you could do with only 1 copy of
Languish in your main and maybe side another copy or two. I'd probably even just side all of them though. Depends of what you expect your meta to play I guess.
Other than that you should be set I think. I hope these suggestions help you out a bit and I wish you lot's of success with the deck.
Ohh, just remembered, you might want to look into some hand control cards like
Duress and
Transgress the Mind. Might be worth it since you don't have much draw power, might at least
disrupt your opponent's hand and make them play a bit slower. While also seeing what you'll have to deal with and when to do so, obviously.
Edit:
Read the Bones might be worth testing since it gives you some draw power.