Probably Souls of the Faultless, because even though I have never played with/against it, it seems like most of the time it would only ever give you 1 trigger, if that. :(

Alright, made the switch, Souls of the Faultless is out, Noble Purpose is in. Curve is looking like decending stairs. Is 6 rocks going to be good enough? Or do I need more than 36 lands? Maybe both lol

Well I did some searching and I think you could actually improve the lifegain trigger cards actually! Here's what I think could be removed:
Drana's Emissary
Nyx-Fleece Ram
Suture Priest
Vampire Nighthawk
Wall of Reverence
Zulaport Cutthroat
Angel's Feather
Demon's Horn
Loxodon Warhammer
Ajani's Mantra

I think the following could replace them:
Moonlit Wake
Umezawa's Jitte
Contemplation
Auriok Champion
Profane Memento
Deathgreeter
Patron of the Kitsune
Shattered Angel
Sangromancer
Falkenrath Noble

Honorable mention lol:
Noble Stand

But to answer your question, your curve should still look fantastic before or after any of my suggested changes. Don't worry about the descending stairs bit, it just means you can play more 3-5 drops instead of the 1-2 drops you're playing :D

Umezawa's Jitte is on the aquireboard. Auriok Champion would be fantastic but budget constraints adding the fact umezawa's is already over $30. Loxodon Warhammer was there more to provide trample and lifelink to Karlov. Most of what you suggested I've looked at too and thought those might be nice. Its just they seem to all require creatures to hit the yard to do anything. Karlov exiles so that doesn't synergize. I just feel that if I run those I need another wrath or two :) Or possibly more removal, which I'm not opposed to running. The only problem with more wraths is Karlov won't get any benefit if he gets wiped out as well.

Then again, in a multiplayer game there will be a lot of creatures dying especially if there is a sacrificial theme.

Well, Blood Artist, Bloodchief Ascension, Profane Memento, Falkenrath Noble, Deathgreeter, and Moonlit Wake (and any other effects like that) are either good enough or not good enough, so I would highly recommend either running all of them or none of them. You know what I mean?

Yeah, its either I get to wait until my upkeep for triggers or hope something dies. Honestly I'm tempted to remove all the cute life gain on upkeep/death for extort critters. At least I can get a trigger or two off before the attack phase. I'll have to playtest this though as solitaire really doesn't paint the whole picture

I'm not going to update the list until I playtest the following:

Out

Zulaport Cutthroat

Cradle of Vitality: going to need all my mana for extort

Angel's Feather

Demon's Horn

Wall of Reverence

Ajani's Mantra

Nyx-Fleece Ram

Falkenrath Noble

Deathgreeter

Drana's Emissary

In

Blind Obedience

Thrull Parasite

Basilica Screecher

Syndic of Tithes

Basilica Guards

Kingpin's Pet

Knight of Obligation

Syndicate Enforcer

Pontiff of Blight

Tithe Drinker

Though I'm wondering if I should drop some of the high cmc cards like Serra Avatar

They're not bad ideas, but if you don't like extort either, then the upkeep triggers and activated abilities are the next best things.

The only downside is that I'll have to balance extort with karlov's removal. Lowering the curve would help. I'll go ahead And update the list just so I know where I'm at. Going to clean up the comments too if I can figure that out lol

You could always use Illusionist's Bracers and Rings of Brighthearth to abuse his ability... :D

Changes: (these are provisional until tested)

Loxodon Warhammer >>> Tablet of the Guilds: it's like a two for one deal, Angel's Feather + Demon's Horn . Not sure if this will stick around in the deck.

Chalice of Life >>> Ajani's Mantra: seems I only get one trigger from it most the time. I will miss the ping dmg though.

Sunbond >>> Nyx-Fleece Ram: the aura is amazing but paints a big target and no way to get it back.

Bloodgift Demon >>> Drana's Emissary: card draw is good but no synergy.

Planar Cleansing >>> Tragic Arrogance: a better wrath

Whatcha think?

If you really want a Tablet of the Guilds effect, Contemplation is probably better. :) everything else seems good

Contemplation is already in there :) Yeah I opted for the upkeep triggers instead of on creature death. I have seen Karlov lists that have a sacrificial themes to it and they would better utilize Falkenrath Noble and co. These changes also lowered the curve a bit allowing for more extort action. If extort isn't as glorious as it sounds with karlov then I might implement the gy trigger cards.

Playtested the deck in a 5 man game at the LGS and overall it did quite well despite a glaring setback. I was heavily mana screwed (only had three lands the entire game) but still survived somehow until about T9. A T1 Soul's Attendant lead to a T2 4/4 Karlov. T3 I had Tithe Drinker. t4 I had an Ajani's Pridemate. I was able to kill off one player by T5 from general damage and put 10 Commander on another. After that the game stalled for me as I was keeping land open to exile threats, just not enough to exile an infect flier which finished me off.

Observations

1. Karlov is a blast, everyone is afraid of him. He was a 38/38+ after a certain point and that's after being removed as a 26/26...

2. He needs evasion or he just sits there getting fat. Getting fat leads to being a big target. This is especially true for pods of 5 or more.

3. Extort actually works okay, but I might drop Pontiff of Blight due to cmc for something else.

4. More lands? Or I need to shuffle better.

5. Protection is essential. While he is only a 2 drop which helps a lot, he quickly gets fat

6. He is very capable of knocking out an opponent or two within the first two turns. Especially with a T1 Soul Warden.

7. I imagine token/swarm strategies, infect and wraths are Karlov's biggest enemies. Granted the extra life gained helps with this. I had 94 life before infect got me.

So I plan on making some changes. Mostly cutting some cute life gain stuff for evasion

On #6 there was a typo, damn you auto correct... I meant he can knock out a player in the first FEW turns, not two.

Maybe I should make a list of commander protection? Stuff like Lightning Greaves, Darksteel Plate, etc.

That would be lovely :)

Considerations

I'm just spit balling here. Anything I can think of that will protect Karlov and allow him to hit opponents or offer protection I'm just listing out.

Trailblazer's Boots: evasion

Unquestioned Authority: protection, evasion, and card draw

Eternal Thirst: evasion, lifelink and synergizes well with Karlov

Pentarch Ward: card draw, evasion, protection

Whispersilk Cloak: evasion and shroud.

Loxodon Warhammer: lifelink and trample

Righteous War: pro white and black for all my creatures. May be no bueno with the deck however.

Spirit Mantle: evasion

Holy Mantle: evasion, but a weaker version of Spirit Mantle

Samite Elder: pro white and black. Avoids a fair bit of removal.

Akroma's Memorial: protection, evasion, and a little bit of everything.

Pledge of Loyalty: pro white and black to a creature.

Sun Titan: a way to recur lost enchantments/aura/creatures/ect.

Changes for now:

Ajani's Mantra >>> Eternal Thirst

Nyx-Fleece Ram >>> Trailblazer's Boots

Pontiff of Blight >>> Whispersilk Cloak

Angelic Accord >>> Pentarch Ward

Tablet of the Guilds >>> Loxodon Warhammer

Syndicate Enforcer >>> Unquestioned Authority

Wondering if I should switch Kokusho, the Evening Star with Sun Titan. I think I'd get better use from titan.

Additional Changes:

-Kokusho, the Evening Star: 6 cmc and has to die to be synergistic

-True Conviction: sort of a win more card

-Blood Baron of Vizkopa: the protection is nice but Divinity is better

+Greed: more card draw, less expensive then Erebos and no worries of it being stolen

+Essence Harvest: others have noted how nice this card is, especially with how quick Karlov gets fat. It can easily one shot an opponent which in a multiplayer format is needed.

+Ob Nixilis of the Black Oath: he can extort and drop a fatty every other turn. His ultimate might be worth it using his own demons as targets.

Looking to add Hatred but not sure what to cut for it. Combos well with Essence Harvest or can be a finisher on an evasive Karlov.

Changes

Wrath of God >>> Divine Reckoning: wrath that spares Karlov

Merciless Eviction >>> Sun Titan: recurs auras, and weak extort critters that hit the bin

Eternal Thirst >>> Gift of Orzhova or Angelic Gift: Somehow I missed Eternal Thirst doesn't give flying. Orzhova synergizes well and Gift nets me a card... mmm decisions.

Righteous Cause, Noble Purpose, and Polluted Bonds on the cutting block. While each card is amazing often I find myself saving the mana that could be used on these to exile threats or saving for an extort. Might place in some of the upkeep triggers back in like Ajani's Mantra or the on death triggers like Moonlit Wake. Haven't decided. Might even add more evasion cards

I hate to be that one guy but first of all, here is a list you can look at to help Uncle Karl Says You Gotta Pay Rent. Secondly to sum it up, I opted for a little more board presence, little more recursion and a little more card draw; instead of using a lot more removal. The creatures are mostly in the form of tokens. With all the ETB triggers from our Soul Sisters, it guarantees a good sized Karlov of the Ghost Council. Not to mention it helps stabilize the board. Academy Rector is possibly a good thing here if money allows. I also like the idea of Darkest Hour + Teysa, Orzhov Scion , which gives us grounds for basically indestructible creatures. There is also an enchantment only version of Felidar Sovereign: which is Test of Endurance. Hopefully this helps you some.

I was contemplating adding in an Elspeth for token gen/life gain. I'd love a Bitterblossom but with Christmas around the corner I would have a lot of splainin to do to the wife :) As of right now my token producers are in the form of planeswalkers. Darien, King of Kjeldor may also be a nice include if you want tokens. He works nicely with anything that deals dmg to you, like City of Brass or Caves of Koilos. I'm opting for more of a voltron style build so if I added Teysa in I would have to do a bit of rewiring for a sacrificial theme which currently is only supported by Blood Artist. The auras I put in mostly have a dual purpose. Those that give protection from creatures/colors allows for an unblocked Karlov that is immune to abilities of creatures. So in a way its both protection and evasion. Pentarch Ward and Unquestioned Authority also nets me a card so if it gets destroyed I at least replaced it. All of the auras i run can be recurred by Sun Titan as well. Debtors' Knell or Oversold Cemetery have been on my radar as possible includes.