Wither & Die
Aim
The idea behind this deck is to cast creatures with wither, then rapidly remove -1/-1 counters from these so they become big hitters with high toughness.
Then when they have amassed -1/-1 counters on opponents creatures start a chain reaction of creatures dying by subsequently moving those counters around using Blowfly Infestation, hopefully board-wiping an opponent and leaving just enough counters on my creatures so that they survive.
This is then followed by a rapid removal of the counters on my creatures again via creatures such as quilspike or casting green and black spells to remove counters from Noxious Hatchling or regenerating Deity of Scars.
A conventional game for this deck normally sees Woodlurker Mimic hit the board of turn 2 followed by a Rendclaw Trow on turn 3 turning the mimic into a 4/5 and providing an early big hit against my opponent. Past this a Noxious Hatchling or a Deity of Scars are the next creatures to aim to have out, the benefit of playing Noxious first is that counters come off it quicker in subsequent turns due to the fact most spells in the deck are dual colour.
Once Blowfly Infestation hits the board the maths begins, with opponents being reluctant to swing in case the -1 storm starts and board wipes everyone. If I've got Melira, Sylvok Outcast out by this point then it really deters opponents. Melira also ensures Rendclaw Trow stays on the board regardless of what happens to it.
Key Combos
Blowfly Infestation + Noxious Hatchling
Establish -1/-1 counters on opponents creatures until they hit critical mass and start pinging around the battlefield killing everything in their path.
Melira, Sylvok Outcast + Noxious Hatchling
Melira ensures Noxious comes in as a 6/6 straight off the bat.
Melira, Sylvok Outcast + Rendclaw Trow
Perpetually persistent Rendclaw.
Noxious Hatchling + Quillspike
Taking counters of Noxious makes Quillspike a possible 13/13.
Main Board
Deity of Scars
A high toughness big hitter where the removal of its -1/-1 counters is a double benefit in that it regenerates it and makes it bigger.
Melira, Sylvok Outcast
If out on the battlefield first ensures Noxious Hatchling and Deity of Scars enter the battlefield at full force and when the -1 storm starts with Blowfly Infestation that my creatures stay alive.
Noxious Hatchling
One of the key creatures with wither. As all the cards in this deck are both black and green the -1/-1 counters rapidly drop off making it a 6/6 with wither for only 4 mana (plus the benefits of whatever you cast to get the counters off).
Quillspike
Can be made massive by improving my other creatures. For example if a Noxious Hatchling has been cast on the previous turn I can then pay 4 mana to make Quillspike a 13/13 whilst removing all the counters from the Hatchling. This also keeps the -1/-1 counters at an acceptable level if the they start flying around due to Blowfly Infestation.
Rendclaw Trow
Can be made to be very persistent if the -1/-1 counter it acquires when dying is removed by Quillspike over and over again. It is also a useful at putting -1/-1 counters on opponents creatures.
Woodlurker Mimic
Almost every card in the deck is both black and green which means it'll be turning into a 4/5 with wither on most turns and is therefore very useful at putting -1/-1 counters on opponents creatures.
Vraska the Unseen
A nice little distraction for opponents as I slowly wither their creatures to death, and if timed right a Blowfly board wipe can leave their defences open for a black assassin creature to win the game.
Blowfly Infestation
The key to the deck, as it allows the -1/-1 counters I have established on one or more opponents creatures to be moved to one creature after another when one dies. This ability is a potential board wipe if played correctly.
Gift of the Deity
The deathtouch ability is useful, having every creature block something with wither and deathtouch is ridiculous. Deathtouch allows me to control the amount of -1/-1 counters that will exist on opponents creatures such that they only end up killing theirs rather than all of mine when they get moved around.
Golgari Charm
Its -1/-1 allows the -1/-1 storm to be triggered if a particular creature is close to dying, regenerating each of my creatures if also quite useful. This card forms part of the thematic Golgari element in this deck.
Contagion Clasp
Once -1 counters have been established on opponents creatures, allows me to control when the -1 storm will start and-or wither away larger threats. It also allows me to accelerate Vraska's loyalty counters such that I can have the 1/1 game winning creatures out by turn 6.
Sideboard
Spidersilk Net
Provides the deck with flying defence and also contributes towards my creatures surviving an accumulation of -1 counters if the storm begins.
Disclaimer
All my deck centre around trying to do one or two things well based around a certain theme, they are not intended to be able to defend and cope with everything and anything that comes their way. (Good Card Suggestions vs Deck Dilution)
I am a 'kitchen table' player with a limited budget. As with all my decks advice and suggestions (as well as +1's) are always very welcome but keep in mind anything above the $5 per card mark I'm unlikely to consider.
The more reasoning you can give with any suggestion you make, the more likely I am to consider running it in the deck. This is because I can't always spot the combo or idea you are going for. Letting me know what your thinking gives me a better insight into how you think this deck might be made better by the suggestion.