You've got life gain pretty well covered by most of your creature base, which is great, but to what end? You don't win by increasing your life total. You've got the start of something pretty nice here though. Here's my suggestions:
Cut: Nyx-Fleece Ram - Cute but slow Tymna the Weaver - Not the right deck for this guy as you're not going to be swinging each turn. Drana's Emissary - Too slow Wall of Reverence - Too slow Rhox Faithmender - Sort of redundant Obzedat, Ghost Council - Not the right deck for him Kaya, Ghost Assassin - Not the right deck for her Ajani's Mantra - Too slow Sanguine Bond Exquisite Blood - I know these go infinite, you'll probably find not too many people happy to see it though. I'd keep sanguine and lost exquisite. Thought Vessel - It never hurts to be sure of course, but this doesn't seem the sort of deck you'll be 7+ all that often. Alhamarret's Archive - Seems a bit winmore. The double life gain is irrelevant to you, you want separate instances of life gain. The double cards is fun, but there are probably better options for you. Righteous Confluence - Just not a fantastic card by any stretch.
As far as Planeswalkers go, I disagree with toctheyounger77 about Kaya, Ghost Assassin. I think her all of her abilities are relevant, although it is her card draw and flicker that I can see myself using the most. I do however agree with him about Sorin, Grim Nemesis. Taxing your opponents life total and increasing you card advantage is very helpful, and his ultimate can win a game outright.
One thing you will want to stock up on is ways to EXILE enchantments. Erebos, God of the Dead will ruin you day, and he is the first thing any competitive minded black player will tutor for. Having him show up as commander is also possible. There is a guy I know with a mono black toolbox deck that has 7 legendary creatures in it, and he will change commander depending on what everyone else is playing. I would make adding Anguished Unmaking and Utter End a priority. Also helpful is Oblation, Ayli, Eternal Pilgrim, and Return to Dust.
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So I'm guessing you want some feedback for the deck?
Is there anything particular you want to do with the deck besides gain a ton of life and exiling creatures to your heart's delight?
And that's what you need to think about. You have a million ways to gain life but no major plan for winning. Karlov could go voltron, you could go bleeder/attrition, reanimator, you have options. You just need to give us a direction you want to head in, as it will heavily impact the cards we suggest.
Feedback is always welcome.
(editing lands at a later time)
2 Karlov of the Ghost Council
Creatures (26)
1 Soul's Attendant
1 Soul Warden
1 Mother of Runes
1 Serra Ascendant
1 Deathgreeter
2 Auriok Champion
2 Nyx-Fleece Ram
2 Blood Artist
3 Kambal, Consul of Allocation
3 Tymna the Weaver
3 Drana's Emissary
4 Wall of Reverence
4 Crypt Ghast
4 Cliffhaven Vampire
4 Rhox Faithmender
4 Falkenrath Noble
4 Ranger of Eos
4 Disciple of Bolas
5 Sunscorch Regent
5 Obzedat, Ghost Council
5 Agent of Masks
5 Shattered Angel
5 Bloodgift Demon
6 Pontiff of Blight
6 Sun Titan
7 Defiant Bloodlord
4 Kaya, Ghost Assassin
5 Ob Nixilis of the Black Oath
6 Sorin Markov
Enchantments (12)
1 Blind Obedience
1 Authority of the Consuls
1 Bloodchief Ascension
2 Ajani's Mantra
3 Phyrexian Arena
3 Underworld Connections
3 Retreat to Hagra
3 Ghostly Prison
3 Aura of Silence
5 Sanguine Bond
5 Exquisite Blood
5 Polluted Bonds
Artifacts (11)
1 Sol Ring
1 Elixir of Immortality
2 Orzhov Signet
2 Tablet of the Guilds
2 Thought Vessel
2 Umezawa's Jitte
2 Sword of War and Peace
3 Pristine Talisman
4 Well of Lost Dreams
4 Aetherflux Reservoir
5 Alhammarret's Archive
2 Demonic Tutor
3 Read the Bones
3 Sign in Blood
3 Night's Whisper
3 Exsanguinate
3 Death Grasp
4 Diabolic Tutor
5 Debt to the Deathless
5 Fumigate
5 Righteous Confluence
Instants (2)
1 Enlightened Tutor
6 Beacon of Immortality
Land (36)
18 Swamp
18 Plains
Maybeboard
6 Kokusho, the Evening Star
6 Felidar Sovereign
5 Divinity of Pride
5 Archangel of Thune
5 Gray Merchant of Asphodel
3 Pious Evangel
2 Ayli, Eternal Pilgrim
2 Suture Priest
2 Zulaport Cutthroat
1 Soulmender
You've got life gain pretty well covered by most of your creature base, which is great, but to what end? You don't win by increasing your life total. You've got the start of something pretty nice here though. Here's my suggestions:
Cut:
Nyx-Fleece Ram - Cute but slow
Tymna the Weaver - Not the right deck for this guy as you're not going to be swinging each turn.
Drana's Emissary - Too slow
Wall of Reverence - Too slow
Rhox Faithmender - Sort of redundant
Obzedat, Ghost Council - Not the right deck for him
Kaya, Ghost Assassin - Not the right deck for her
Ajani's Mantra - Too slow
Sanguine Bond
Exquisite Blood - I know these go infinite, you'll probably find not too many people happy to see it though. I'd keep sanguine and lost exquisite.
Thought Vessel - It never hurts to be sure of course, but this doesn't seem the sort of deck you'll be 7+ all that often.
Alhamarret's Archive - Seems a bit winmore. The double life gain is irrelevant to you, you want separate instances of life gain. The double cards is fun, but there are probably better options for you.
Righteous Confluence - Just not a fantastic card by any stretch.
You've got some great stuff on your maybe board there. Add:
Kokusho, the Evening Star - this guy ends games
Divinity of Pride - will almost always be 8/8
Archangel of Thune - Great synergy with Karlov
Gray Merchant of Asphodel - similar to koko, he can be a win con on his own.
Suture Priest - Does exactly what you want it to.
Zulaport Cutthroat - Bleeder effect for all your opponents.
I'd also recommend:
Sorin, Grim Nemesis - This is the walker you want in this deck. Even if it's only for the first ability.
Necropotence - The best card draw available in the colours.
Divine Reckoning - Karlov will get huge. This will give him the board. There are variants of this too, such as:
Cataclysm
Tragic Arrogance
Cataclysmic Gearhulk
Death Cloud
Killing Wave
and so on.
Blood Artist - redundancy for your cutthroat and noble.
Noxious Gearhulk
Worn Powerstone, Mind Stone, Hedron Archive, a couple more mana rocks in general.
I know you said you haven't touched your manabase yet, and this probably goes without saying, but Cabal Coffers and Urborg, Tomb of Yawgmoth. They will make Exsanguinate and Debt to the Deathless into win conditions.
Hope this all helps, and good luck.
I have personally cut Deathgreeter, Blood Artist, Zulaport Cutthroat, and Falkenrath Noble because I have other decks that focus on sacrifice mechanics, and I wanted to be different with Karlov. If you do go the sacrifice route I have found both Gutless Ghoul and Dross Harvester to be allot of fun.
As far as Planeswalkers go, I disagree with toctheyounger77 about Kaya, Ghost Assassin. I think her all of her abilities are relevant, although it is her card draw and flicker that I can see myself using the most. I do however agree with him about Sorin, Grim Nemesis. Taxing your opponents life total and increasing you card advantage is very helpful, and his ultimate can win a game outright.
One thing you will want to stock up on is ways to EXILE enchantments. Erebos, God of the Dead will ruin you day, and he is the first thing any competitive minded black player will tutor for. Having him show up as commander is also possible. There is a guy I know with a mono black toolbox deck that has 7 legendary creatures in it, and he will change commander depending on what everyone else is playing. I would make adding Anguished Unmaking and Utter End a priority. Also helpful is Oblation, Ayli, Eternal Pilgrim, and Return to Dust.
Is there anything particular you want to do with the deck besides gain a ton of life and exiling creatures to your heart's delight?
BGU [Primer] Sidisi, Brood Tyrant BGU | BG [Primer] Mazirek, Kraul Death Priest BG | G [Primer] Polukranos, World Eater G
My YouTube Channel:
The Commander Tavern - a channel I just started where I'll post deck techs and gameplays. Please support by checking it out. Maybe you'll like its content and subscribe! Thanks!
And that's what you need to think about. You have a million ways to gain life but no major plan for winning. Karlov could go voltron, you could go bleeder/attrition, reanimator, you have options. You just need to give us a direction you want to head in, as it will heavily impact the cards we suggest.
The typical Lightning Greaves, Swiftfoot Boots, Whispersilk Cloak as well as Mother of Runes would help.
Enlightened Tutor will help you find Aetherflux Reservoir and others.