
As you may suspect from this deck's "boss" creature, this deck interacts a lot of the time with the graveyard. And with such a powerful ability, you'll want some big creatures in the graveyard to fuel the Defiler.
Creature (23)
2 Blisterpod
2 Carrier Thrall
2 Loam Larva
2 Rot Shambler
2 Stalking Drone
1 Essence Depleter
1 Voracious Null
2 Netcaster Spider
1 Null Caller
1 Broodhunter Wurm
1 Smothering Abomination
2 Seed Guardian
1 Kozilek's Pathfinder
1 Brood Monitor
1 Baloth Null
1 Dread Defiler
Non-Creature Spells (12)
2 Bone Splinters
2 Oblivion Strike
1 Vines of the Recluse
1 Altar's Reap
2 Corpse Churn
1 Grasp of Darkness
2 Natural Connection
1 Pulse of Murasa
Land (25)
1 Blighted Woodland
1 Evolving Wilds
2 Fertile Thicket
4 Wastes
8 Swamp
9 Forest

With the number of Eldrazi Scions you'll be sacrificing in this deck, this should net you more than a few extra cards. He can always sacrifice himself to draw a card if you have nothing else you want to sacrifice. Plus, he's 4 power so he's a good target for Dread Defiler's ability.

It's a great way to sink in mana you otherwise might not be using, but needing to have those pure colorless sources can prove to be tricky with the deck as currently constructed.
Another notable uncommon from Oath of the Gatewatch is Seed Guardian. When he dies, he replaces himself with an X/X Green elemental creature token, where X is the number of creature cards in your graveyard. This obviously gets better as the game goes along.

To fuel the graveyard, it's probably good to have another copy of Smothering Abomination. You'll also want some top end threats such as Oblivion Sower or World Breaker to make the Defiler's ability more threatening.
These two Eldrazi are pretty menacing The Sower is a big presence and can steal opponent's lands, too. World Breaker helps to exile one of your opponent's more important cards while being a 5/7 with reach.
There are 4 copies of Wastes, the colorless Basic land, already in the deck. But you'll probably want at least a few more. Also, a couple more copies of Blighted Woodland provide a stable source of pure colorless mana that can give you additional mana ramp in the late game. Also, Grasp of Darkness is solid removal that you can easily add a few more copies of to the deck.
"Vicious Cycle" does provide a useful base from which to launch a Green/Black Eldrazi deck, but it may not be the most consistent at winning with the Defiler. The deck depends on you being able to cast your bigger creatures before your opponent has any way of dealing with them. Eldrazi Ramp has already proven to be a playable deck, especially when you add creatures such as Wasteland Strangler and Blight Herder to the mix.
Adding White allows you to exile creatures with Silkwrap and Stasis Snare and fuel the Stranglers and Blight Herders. Also, White gives you access to Eldrazi Displacer which has an infinite combo with Brood Monitor and Zulaport Cutthroat to drain your opponents to death.
There are plenty of different directions you can go with this deck, but honestly the best top end finisher you can choose is Ulamog, the Ceaseless Hunger. As a starting place for a Green/Black Eldrazi deck, it's solid enough, offering a good balance of useful creatures, mana ramp, creature recursion and removal. But there's plenty of room for improvement.