Ahh, ok i understand what you mean. Also the
whip of erebos would be good in a variety of black/ any other color type of deck. If you repeatedly summon the grey merchant of asphodel with a large group of black devotion permanents then you'd have a large health swing. Personally I don't have the whip but with the grey merchant I like to play him, sacrifice him using bone
splinter or something, then cast escape from the underworld to bring him and another creature back. I like playing the returned creatures so adding
returned centaur and
returned reveler makes a zombie deck very
dangerous. You wouldn't even have to play and instant or sorcery spells, just creatures to mill out the deck and steal health. Those would be some excellent additions to this deck as well since you're playing commander and every card is a single. Mill isn't always encouraged when larger decks are involved but your opponent only has 1 copy of every card in his deck.
Returned centaur enters the battlefield and he mils 4 cards,
geralf's mindcrusher mils 5 and
rotcrown ghoul also mills another 5 when it dies. Try putting those in an
unearth deck and watch the fun begin.