Moar Foul-Tongue Shriek! Foul-Tongue Shriek is awesome! I also suggest adding a few Duress/Transgress the Mind. +1!

I really like this deck! I play one very similar and have found that Retreat to Emeria works really well to keep rally triggers hitting. You might also consider dropping Kalastria Nightwatch for a playset of Drana's Emissary since they're so hard to deal with when you have more than one on the board. I'm also running Dazzling Reflection as an answer to Eldrazi ramp. Let us know what kind of records it puts up! +1

Also, Vampiric Rites is great for card draw, and triggers Zulaport Cutthroat.

Only suggestions I can think of are Bloodbond Vampire and Serene Steward since you have lifegain focus.

Sorry if I've said that already. Hard to remember what's cleared comments and what's new with all these similar decks popping up. :)

If you can manage to get Gideon, Ally of Zendikar them it would help, his 0 ability can trigger more allies.

Also if you are going to put a retreat in, then add fetch lands if not remove it and put in more removal like Grasp of Darkness or Ruinous Path or even Silkwrap