I recommend adding cards that create tokens (in your case it would best be zombie tokens) that you can repeatedly sacrifice for card advantage. For example; if you were to have
nephalia smuggler on the field with
geralf's mindcrusher and constantly kill it with
vampiric rites, then you'd be able to gain 1 life and draw a card for two mana, mill your opponent for five cards every time your zombie dies and re-enters the field because of its own undying effect, and
nephalia smuggler would
flicker your creature so it's +1/+1 counter would keep resetting. This way you would have a big guy that wont stay
dead and an opponent who's health (and deck are always on the clock). If you did decide to take the zombie route then you'd probably want to cut back on the snakes and lean towards cards like
ghoulcaller gisa and creatures that make zombie tokens upon dying or have the undying effect. Just food for thought.