Vengevine is your main kill condition, and there are a few ways to make use of him. Putrid Imp and Lotleth Troll are your primary creature enablers, as their discard abilities can bin as many Vines as you need at no cost to you, and can even give a permanent boost to your board power in the case of the Troll. The two also combo nicely with Blood Scrivener. Simply discard any cards you need in the graveyard or don't need at all and watch the extra draws come in. Your two discard outlets, as well as the Scrivener, are all Zombies as well. This means they allow for some great synergies with Gravecrawler.

Speaking of Gravecrawler, this undead rock star is key to really pushing out those Vengevines. Along with Basking Rootwalla, you should have no trouble whatsoever casting that second creature to trigger the Vine's reanimation. Cabal Therapy is a great defensive spell that also combos with Gravecrawler, and in some situations even Vengevine itself: if the only creature you have to cast is a Gravecrawler, feel free to play him, sacrifice him to Therapy and then play him again, triggering any Vines you have with just one Zombie. Carrion Feeder is an attrition beater that can feed off Crawlers to get bigger than anything else thrown at you.

Buried Alive is your enabler in spell form, and it can pack a punch! Grabbing three Vines is the obvious play, as it can end the game in a hurry. Grabbing three Gravecrawler is not out of the question either. Crippling Fatigue is another great option that can be tutored up if Smother is not available. It should also be noted that the cards don't all have to be the same; any combination of the three mentioned cards could all be justified in some situation or another. Grisly Salvage is, to a lesser extent, in the deck for the same reason as Buried Alive. The difference is it can dig for a discard creature if needed, while still pitching those that would prefer the graveyard.

Sideboard Suggestions-
Combo should be combated with discard. You already have Cabal Therapy, so throw in some Duress and call it a day. As far as graveyard decks go, you should know your options by now. Just don't play Planar Void or similar cards, as you need the graveyard just as much as anyone you would bring it in against.

Discard will help against control as well, but you also want to think about what they will bring in against you. Krosan Grip and similar cards can get rid of the permanent types of graveyard hate. If you have them or can afford them, Abrupt Decay again deserves a mention. Finally, Krosan Reclamation is a little cute, but can save you from Surgical Extraction-style cards, so it's worth a look.

Aggro decks can be handled pretty easily with black removal. One I have yet to mention that can pack a punch is Deathmark, but really anything works. Attrition is a favorite of mine that just destroys most creature-based decks, thanks to your four main deck Gravecrawler. Go ahead and try it out, it's hilarious.