From my experiences playing Tribal decks I would advise you reconsider the zombie theme. I found that they rarely have individual standout cards, and I struggled to get enough out to pose a threat for more than a turn, and one wrath can take a while to recover. I concede that you have Balthor in the deck, but you need to pay 7 to remove him the first time, and 9 the second, making it difficult to pull off.
I would suggest instead opting for a range of big black spells that really work overtime, so that you don't need as many pieces, and use Balthor for big game swinging moments.
Creature wise I would suggest adding
Chainer, Dementia MasterDrana, Kalastria BloodchiefGeth, Lord of the VaultPhyrexian ObliteratorRune-Scarred DemonNirkhana RevenantAvatar of WoeVisara the DreadfulButcher of MalakirMassacre WurmScion of DarknessSheoldred, Whispering OneExtractor DemonI also recommend to get maximum mileage out of your Crypts and Coffers
VesuvaDeserted TempleExpedition MapI played a Thraximundar deck that used mass graveyard as it's central theme, which worked for a while, until Wizards printed
Bojuka Bog (Speaking of which, I would strongly consider this) and
Nihil SpellbombThey pretty much killed the deck, it either wins gloriously, or fails completely.
That's partly because I target myself with
Traumatize and play
mesmeric orb and other similar spells.
Living death should get a look in, and I'm a firm believer that any mono colour deck should be running
Strip Mine and
Wasteland as dealing with a problem land is often worth the lost land drop. In no way am I suggesting you strip lock someone, I just think that there are certain lands that need to die on sight.
