Zombies Zombies Zombies

I really like how Soulless One still plays off of Marrow Chomper even after it devours some zombies. Just gobble up several of your weaker zombies or your zombie tokens that aren't needed, and not only does Soulless One remain powerful, but Marrow Chomper grows in strength.

Undead Warchief is also a great addition to this deck seeing as with him in play, it becomes insanely easier to play your Endless Ranks of the Dead and Army of the Damned, and to top it off all of which will be buffed up by his +2/+1.

Some card additions you could try would be Moan of the Unhallowed or Cemetary Reaper. Moan of the Unhallowed wouldn't give an amazingly substantial benefit considering you already have a few token-creating zombie spells, especially with Parallel Lives which is awesome in this deck by the way, but would help if you seem to be lacking the mana to play Army of the Damned, et cetera.

Personally I think Cemetary Reaper would be very nice in this deck, and here's why: With Marrow Chomper eating up your cards like Walking Corpse, Diregraf Ghoul, and perhaps other cards, you can just have it poop them out and either feed them back to him or have them added to your token army. But if you plan to bring those back with Ghoulcaller's Chant, you can still spawn tokens by exiling cards from an enemies grave! It also might be nice to have more +1/+1 counters on your zombies as well, which should never be overlooked.

In the end this is a really nice deck that is well made and I enjoy seeing people using black/green for zombies because of how uncommon that is lol. +1 like from me!