Ramp:

Gyre Sage: Mana Dork

Solemn Simulacrum: (R) Basic to play tapped. Repeatable with Glissa

Sol Ring: Mana Rock

Fixing/Consistency:

Expedition Map: (R) Any land to hand. Repeatable with Glissa

Other: 

Jet Medallion: Black spells cost 1 less

Sword of Feast and Famine: Untaps all lands

Draw: 

Ob Nix Reignited: (R) +1: Draw a card, lose 1 life

Phyrexian Arena: (R) Draw a card, lose 1 life

Deathreap Ritual: (R) Draw 1 card at the end of a turn where a creature died

Read the bones: Scry 2, Draw 2, Lose 2 life

Solemn Simalcrum: (R) Draw one on death. Repeatable with Glissa

Nihil Spell Bomb: (R) Draw one when going to grave. Repeatable with Glissa.

Removal:

(R) Repeatable

Permanent: 

Beast Within: Gives player a 3/3 beast instead

Maelstrom Pulse: Destroy all tokens/cards on board with same name as target

Song of the Dryads: target becomes forest

Non-land Permanent: 

Vraska: (R) Destoy target on -3

Abrupt Decay: Destory target with cmc 3 or less

Non-Creature Permanent: 

Woodfall Primus: (R?) On ETB, destroy. Persist

Land: 

Creature: 

Glissa: (R), Deathtouch, First Strike

Sourceress Queen: (R) target becomes a 0/2

Reaper of the Wilds: (R?) Deathtouch

Skinrender: 3 -1-1 counters

Vhati il-dal: (R) target power or toughness becomes 1

Grim Poppet: remove self -1-1 to give target -1-1 counter. starts with 3 counters

Dismember: Target gets -5/-5 until end of turn

Hero's Downfall: Destroy target

Putrefy: Destroy target

Sudden Spoiling: target players creatures become 0/2

Black Sun's Zenith: (R) X -1/-1 counters

Incremental Blight: 1 target gets 1 counter, 1 gets 2, 1 gets 3

Crumbling Ashes: (R) per controller's upkeep, kill a creature with a -1/-1

Ob Nix: (R) Destroy target on -3

Garruk, Apex Pred: (R) Destroy target on -3

Executioner's Capsule: (R) Destroy Target. Repeatable with Glissa.

Artifact: 

Wickerbough Elder: (R?) remove a -1-1 on self to destroy, starts with 1

Putrefy: Destroy target

Sylvok Replica: (R) Destroy target. Repeatable with Glissa.

Enchantment: 

Wickerbough Elder: (R?) remove a -1-1 on self to destroy, starts with 1

Sylvok Replica: (R) Destroy target. Repeatable with Glissa.

Planeswalker: 

Hero's Downfall: Destroy target

Garruk, Apex Pred: Destroy Target on +1

Kamahl, Fist of Krosa is just mean in this deck... But consider it.. just in case.

Notes:

1. Only 1 infect creature. Not likely to cause problem

2. Consider static pump effects for creatures that intentionally carry -1/-1 counters

3. Deck probably needs some land ramp or consistency spells

4. Needs early game creatures added. Ramp maybe?

Weaknesses:

1. Low life gain

2. Few draw sources

3: Low creature count

4. Few wipes

5. May have difficulty with fast decks

6. May have difficulty with +1/+1 decks:

7. May have difficulty with Flying + Hexproof creatures

8. Weak commanders for theme

9. -1/-1 may hurt self as well

10. Little ramp

11. Deck's creatures that hold -1/-1 to do effects are fragile

12. Little recursion

Notable possibilities from Sideboard:

Dusk Urchins: possible 3 cards drawn on death (normal). At least 1 draw. (Could be more with pump)

Deity of Scars:  is a large regenerate creature with upside from -1/-1

Strengths:

1. Opponents creatures get weaker and weaker.

2. Proliferate gets through hexproof and shroud

3. Proliferate will boost Planeswalkers

4. Glissa supports proliferate

5. Vhati il-dal supports killing things

6. Gain control of opponents creatures with -1/-1 counters

7. Use Wickerbough Elder or Grim Poppet with Torture to destroy things

8. Use Quillspike to remove -1/-1 counters from own creatures to pump quill spike

Tokens: 

Flourshing Defenses: gain a 1/1 elf for each -1/-1 given

Tutor:

Demonic Tutor: Sorcery - To hand 

Vampiric Tutor: Instant - To top of deck

Life Gain:

Garruk Apex Pred: Gain life when destroying a creature

Proliferate:

Core Prowler: (R) proliferate on death. Repeat with Glissa

Plaguemaw Beast: (R) Sac a critter and tap to proliferate

Grim Affliction: Spell, Proliferate on cast

Throne of Geth: (R) Sac an artifact to proliferate, Repeatable with Glissa

Contagion Clasp: (R) pay and tap to proliferate

Contagion Engine: (R) pay and tap to proliferate twice

Wipes:

Black Sun's Zenith: (R) Creatures

Pernicious Deed: Creatures, Artifacts, Enchantments

Analysis:

-1/-1 sources

Repeatable:

Corrosive Mentor: All black creatures have wither

Necroskitter: Wither

Core Prowler: Infect

Harbinger of Night: -1/-1 for each creature per controller's upkeep

Lockjaw Snapper: Wither

Noxious Hatchling: Wither

Carnifex Demon: ability to add -1/-1 to each creature by removing a -1/-1 from itself. Starts with 2 counters.

Midnight Banshee: Wither. -1/-1 for each nonblack creature during controller's upkeep

Grim Popper: can remove a -1/-1 from self to give to target. Starts with 3 counters.

Black Sun's Zenith: x -1/-1 to all creatures, shuffle into deck.

Blowfly Infestation: Enchantment, whenever a creature with a counter dies, put a counter on target

Non-Repeatable:

Skinrender: 3 -1/-1 counters to target on ETB

Soul Snuffers: -1/-1 to each creature on ETB

Grim Affliction: Spell, target gets -1/-1 counter

Incremental Blight: Spell, 1 target gets 1 counter, 1 gets 2 counters, 1 gets 3 counters.

Contagion Clasp: Artifact, on ETB target gets 1 counter

Contagion Engine: Artifact, on ETB each creature gets 1 counter

Torture: Enchantment, ability to add 1 counter to enchanted creature

Ob Nixils Reignited from BFZ will be added (Replacing Ob Nix of the black oath)

Drana from BFZ is a consideration