This decks primary goal is to use Varolz and Corpsejack to Scavenge the most cost-efficient creatures I can find in standard. The deck has a few ways to win doing this. I'll go through each card and explain their purpose:

Mainboard:

Corpsejack Menace: Corpsejack is a pretty solid 4 drop, and one of the pivotal cards in this deck. Each time a counter is placed on a creature you control, you place twice that many instead. This can get gross, fast. Each of those Slitherheads in your graveyard can now be scavenged for +2/+2 for 0 mana. This can get really ugly with Hydras (I'm thinking about adding some of these in the future).

Desecration Demon: I picked Desecration Demon over Deadbridge Goliath for a couple reasons. First, he's even better deal to scavenge (Using Varolz). 4 mana for 6/6 is incredible by itself. Combo'd with Corpsejack thats 12/12 for 4 mana. He also can force opponents to make some difficult choices when he's on the battlefield, and he can fly. Incredible deal here.

Bioshift: Here's an awesome combat trick. Thank you Simic for coming up with this. Say you creature is about to get removed thanks to a removal spell, or some other awful thing. Bioshift can take those counters that you spent your hard-earned mana on and move them to another creature so that all you are losing is the creature they were placed on! Granted this takes another creature to be able to use at all, but the bonus is that Corpsejack will DOUBLE the moved counters as well. If he's in play, you basically get to double the counters on the field for 1 green mana. It's a super versatile card in this deck.

Grisly Salvage : This card exists to help fuel the graveyard with prime scavenge material and to help get me some land if I'm having a difficult time drawing it or to grab a pivotal creature from entering the graveyard.

Jarad, Golgari Lich Lord: This guy is the deck's secondary win condition. Done building up your awesome creature with counters, but can't manage to get him through to your opponent's spindown? Sac him instead. You can pretty easily build up a ludicrous number of counters, and that damage goes straight to your opponent. He can also get beefier if you don't happen to grab Varolz till late game and have a bunch of creatures in the Graveyard.

Dreg Mangler : Not a whole lot to say about these guys. They are an awesome 3 drop to put some pressure on, and give me a way to scavenge without having Varolz in play.

Lotleth Troll: This card can get way out of hand super early in the game. The perfect opening hand will involve some land, a lotleth troll and a bunch of Slitherheads. Turn 2, play this guy, discard 3 slitherheads for a 5/4 on turn 2. Scavenge those same 3 slitherheads for a 8/7 on turn 3 ready to swing.

Putrefy: Nice, cheap removal spell that does an awesome job at it. Pretty cheap, and takes care of artifacts (for whatever thats worth) and prevents regen.

Ranger's Guile : Awesome card to stop removal on those creatures you've been building up, can also be played as a combat trick

Slitherhead: This little guy is awesome...as long as he's not on your field. Awesome scavenge material (hard to beat +1/+1 for 0 mana) and an awesome combo card with the lotleth troll. Can also serve a chump blocker or bait to sac for Varolz's regen.

Varolz, the Scar-Striped: Golgari Maze-runner extraordinaire. This guy makes this deck work. Can turn any creature into +1/+1 tokens.

Vraska the Unseen: Vraska is mostly just here for flavor. I find that I use her -3 ability more often than the others, but I have won games with her ultimate before. She can help get rid of pesky permanents, and provide an additional threat that your opponent can't just ignore

Sideboard:

Abrupt Decay: If you're needing more cheap removal this will do wonders

Drown in Filth : Indestructible creature removal (read: Theros Gods) and Graveyard fuel.

Elixir of Immortality: Save that precious Graveyard from getting exiled. Bonus 5 life.

Golgari Charm: What an awesomely versatile card. Protect your creatures from boardwipes Supreme Verdict, Knock out 1/1 token armies, and destroy enchantments. All those options for 2 mana.

Ranger's Guile : Extra one in here just in case you need more!

Treasured Find : This is a neat card I have trouble finding room in the mainboard for. If you have issues with sending critical stuff to the graveyard, this is the card for you.