Abrupt Decay - it's a very powerfull card and a staple in G/B. It allows the removal of creatures, as well as another permanent like Liliana of the Veil. Plus, it can't be countered.
Birthing Pod - this is one of the reasons the deck exists. It's a very good card that creates the chain of creatures that we want. It also has the advantage of having phyrexian mana, which really flexs the mana base.
Brainstorm - Besides Ancestral Recal I believe this is the best cantrip available. Combine it with a fetche or Birthing Pod and you can change your top deck. Buy 3 cards, put 2 that you don't need on the top, and then shuffle with the previous cards mentioned.
Cloudshift - the deck tries to take the maximum power with the ETB effects, and one way to abuse these is with blink. You can even put a Shriekmaw permantly in the game with he's evoke cost and this card. (Pst...you just destroyed 2 creatures of your opponent).
Eladamri's Call - it serves as fixes, not mainly to start the chain, but to get a creature that you need ASAP, like Eternal Witness or Shriekmaw. The deck runs few creatures, so there are times when you'll be starving to have one. This is where this card comes in and it lets you choose the one that you need.
Recurring Nightmare
- this is an impressive card, but since it's mana hunger I only run 2. It's used in the late game, but when it comes is massive. It's a trigger for ETB effects, can bring big guys to the fiels, it helps with spot removal. And it's always recurring.
Sensei's Divining Top - An impressive artifact that makes a huge impact when in play. It's very good to organize the top deck, and it prevents you from drawing big creatures that you don't want at the moment.
Swords to Plowshares - A very good removal that can keep coming back with the help of Eternal Witness.