The Deck I've been using on M15 Duels of the Planeswalkers.
You can easily get the title "The Nemesis" and the achievement "Why Did It Have to be Snakes?" using this deck.
By exploring Theros, you can also get the "Insult to Injury" achievement by sacrificing an opponents Akroan Horse with Bloodflow Connoisseur.
You can also get the "Not again" achievement relatively easily by playing the same spell 5 times from the graveyard. (Masked Admirers, Spider Spawning or with Sheoldred, Whispering One)
It is also possible to obtain Second Life with Death Cultist and Tribute to Hunger but it is a stretch and I'd recommend a different deck if you are actively hunting that achievement.
Obtaining Cards: If you choose B/G you will start with many of the cards you need to get started.
In world 1 Innistrad you should get Prey Upon, Spider Spawning, Bloodflow Connoisseur and Tribute to Hunger. You can also get Necromancer's Assistant, and Cobbled Wings might come in handy if you are struggling with the boss.
In world 2 Theros, you should get Nemesis of Mortals, Satyr Wayfinder to replace your Necromancer's Assistant and Titanic Growth.
In world 3 Ravnica you will get Golgari Guildgate, the important parts of your deck should now be complete and you should easily be able to beat the game.
Death Cultist comes from the last world, but is of relative unimportance and you can use any other 1 cost creature to take it's place, and the rest of the cards are freebies from bonus boosters at the start of the game.
Some tactics:
Raised by Wolves Could easily be replaced with something different, however, I have found the ability to turn a 1/1 into 2, 2/2's and a 3/3 very important for locking out an opponent in a pinch. If you play 2 on the same chump creature, you will suddenly have a 9/9 and 4 wolves.
Bloodflow Connoisseur's ability can be played at any time. If a creature is going to be destroyed outside of combat, just sacrifice it.
Nemesis of Mortals gets cheaper to play the more creatures are in your graveyard and can cost as little to 2 green to play. Bloodflow Connoisseur's ability costs nothing, so if you have some 1/1's in play and need something bulky, you can sacrifice it and swap it out for a 5/5. It's monstrosity ability also gets cheaper, so it can result in some interesting scenarios where you can sacrifice a bunch of creatures during an attack or defence and create a 10/10 on the spot.
Satyr Wayfinder is a great card. Not only does it keep your mana topped up, it also fills up the graveyard to fuel the rest of the decks abilities. You can often play Nemesis of Mortals very early. If you play a single cost creature you can draw Masked Admirers from the graveyard for 2 mana, and play it for a card draw to keep your hand topped up.
Spider Spawning can completely overrun the field and win the game quickly. The bigger the graveyard is, the more spiders you can spawn. However, the really neat thing is that it can be played right out of the graveyard, meaning that if you milled it with Satyr Wayfinder, you can play it whenever you want without it having to be in your hand; you can wait a bit for more spiders for an attack, or you can play it for a defence, and if it IS in your hand, you can play it on 2 consecutive turns. Spiders have reach, so having just a few makes you very safe. Having 9 or 10 can win you the game and it is very easy to do.
Even if a certain boss wipes the field of all your creatures, you can play Spider Spawning from the graveyard and repopulate it.
Prey Upon keeps the opponents side of the field empty and open to attack, you can also use it to take care of fliers, and you can combine it with Titanic Growth. If there are particularly strong enemies Tribute to Hunger and Titanic Growth can take care of those too.
Craterhoof Behemoth and Sheoldred, Whispering One are there just because. playing either one will likely create a win scenario.
