Have you thought about Phelia, Exuberant Shepherd, maybe with Recruiter of the Guard? It's like a nesting egg of weenies, and it's card advantage fwiw.

I really like the idea of making mill work in cEDH... I hate being milled in cEDH, I will never forget losing games that would have been cake walks because some key card was milled (and it wasn't even vs dedicated mill decks, just one off mill for 4 lol), it's not supposed to be good but cEDH decks are so overwhelmingly greedy that something like that can spoke their wheel and cost them the game. Looking at this list makes me feel like not playing Tasha's Hideous Laughter in any blue cEDH list is a mistake, it's really hard to get stuff back from exile and it requires nothing

This is probably not a great suggestion, but maybe it's an 'okay' one... have you ever thought about Inquisitor's Flail? Double mill from your Commander for only 4 mana isn't THAT steep, especially if you pay it over 2 turns, and nobody is ever blocking your Commander so the drawback shouldn't matter.

YMMV but IMHO in cEDH I'd rather resolve a Propaganda than a Crawlspace, if only because people sometimes play Abrade and can then swarm you to death. Most colours are bad at removing Enchantments, but only Black is terrible at blowing up artifacts. I feel like you should also look really hard at Fatespinner, this is an incredibly frustrating Stax effect in mono-Blue, and slowing the game down gives your Commander time to do the thing.

I'm not sure if Resculpt is good or bad in here (a 4/4 is reasonably big), but your Commander is unblockable and with it you can remove an artifact that's really bad for you, OR just exile a problem creature.

What do you think of Dress Down? A lot of things care about creature text, and while turning all of yours off could be bad, it can prevent you from losing the game to a variety of creature based things.

Probably my weirdest idea, would Sunder work in here? The idea is you play it after you're set up to give you a few turns grace while everyone else runs around like headless chickens, I would expect even a couple swings while people try to rebuild could be enough. There is also Static Orb, I feel like as long as you are swinging with your Commmander you don't need to do anything else to gain immense advantage. If Sunder is too much mana you could try Rising Waters maybe, it's only 4 to really slow things down?

If you want to cut something, is there a real plan for Jace, the Mind Sculptor? He's pretty nasty in 1v1, but in a 4 player game I feel like he's too small of an effect for that much mana.

I have an abiding fondness for Necropotence, and I've always been curious if there isn't some crazy things Asmodeus can do, so thanks for posting!

Good Old Gary is a good life gain source in Black, and technically you can reanimate him. People often use it as a win con, so if you're worried you might play it late game and just kill everyone it's a real concern and may not be your cup of tea if you want a more Commander dependent strategy.

If you want a backup Crypt Rats there is also Thrashing Wumpus, which can be activated a couple times. BTW Crypt Rats REALLY likes Gift of Doom in my experience, B to board wipe can give you a lot of time to fart around, and Gift of Doom is one of the hardest to interact with protection effects if you use it's Morph ability to attach it.

I'm not sure it really matters, but I think Elixir of Immortality is better than Feldon's Cane.

I have done some reading on Necrotic Ooze combos (mostly for Meren decks), you can combine Necrotic Ooze in play with Phyrexian Devourer and something like Triskelion or Walking Ballista to win on the spot... Since those work by similarly only applying the activated ability (and not any Static abilities) your idea should work too to draw cards for very cheap (or free with your Skirge Familiar).

I don't think I've ever used it in an EDH deck yet, but Strands of Night is probably worth a look if you like reanimating stuff. I think the issue is I have no mono-black decks, it's much better in mono-black.

Your Feast of Sanity might like Sickening Dreams?

If you don't mind being in Esper, Zur the Enchanter *f-etch* is a great Necropotence based Commander, probably more powerful than Asmodeus, but more of a 'kill on sight' option as a result.

If you like Concordant Crossroads you might also like Mass Hysteria. I feel like the biggest weakness of a deck like this is being wiped, so things that protect you from wipes are incredibly useful.

Things you might want to look at switching out: Bleeding Effect, Sisay's Ring (this is an awful, awful card in a deck that has access to Green ramp IMHO), Worn Powerstone (this is a better card than Sisay's Ring, but not by very much), Candlekeep Sage, Tales of Master Seshiro, Inspiring Roar (this is a very bad card), Silverflame Ritual (see Roar), Lifecrafter's Gift (see Roar), Skyrider Elf, Ogre Sentry, Oakgnarl Warrior, and Abzan Kin-Guard.

Things you might consider to pulling (these are better cards, but there are often much better options): Font of Fortune (just play Night's Whisper please?), Leyline of Abundance (do you have enough mana dorks to justify this?), Omen of the Sea (see Font), Reality Twist (this card is maximum fun but probably does nothing in lots of situations, people are running less and less Basic lands), Basri's Solidarity (maybe play Metastatic Evangel?), arguably all of the 4 mana land ramp spells are kinda risky in here, I feel like you need more veggies like Rampant Growth and Sakura-Tribe Elder to help with early mana, Artifcer's Epiphany (please run Painful Truths over this), Tarkir Doomshaper, Maulfist Revolutionary, and Kin-Tree Warden.

I mentioned a few things worth looking at, but you also might like Najeela, the Blade-Blossom, she's probably the single best Warrior syngery piece. Najeela is VERY GOOD with Derevi, Empyrial Tactician, not sure if Derevi would be 'too good'. I'm sure you've heard of them both, but Karn's Bastion and Gavony Township are great in a counters list, as is good old Atraxa, Praetors' Voice. Finally, you could try Evolution Sage, it's good if you've got a few counters out already. It's in crazy-town, but if you end up using some Proliferate stuff and have lots of creature tokens you might like City of Shadows, I usually lose one or two creatures to it in order to get some decent ramp in a Selesnya deck.

I would look into more Proliferate if you find your deck is already pretty good at getting that first counter on your creatures, especially repeatable Proliferate stuff.

Neat deck idea, but I feel like you probably want more mana sources, definitely some more lands (I'd aim for 36-40 for a 4 mana Esper Commander that you 'need' to have out for your deck to work), and possibly some of the Talismans (some or all of Talisman of Dominance, Talisman of Hierarchy, and Talisman of Progress would be obvious options to consider that help with fixing). My issue is that it's pretty easy to just kill your Commander, at which point you've got a bunch of auras that do very little. You can also throw in some cards to help protect your Commander, more of those could also shave off recasting, but remember something like Swiftfoot Boots needs adds an effective mana to the cost of your Commander (where Lightning Greaves does not), effectively adding 1 to her cost.

You're also pretty light on interaction of some sorts, but I'm guessing you're really, really counting on having your Commander out and stealing the problem creatures, but not everything is a creature in my experience! In White you have access to Generous Gift and Stroke of Midnight, this kind of card can solve a lot of stuff if you're desperate, regardless of the card's type. Maybe removal could be 'Secret Police', ie those who make problems 'go away' forever? I guess you could have Michiko Konda, Truth Seeker in charge?

Eldrazi Conscription can steal something bigger for you, and make it a HUGE problem fwiw.

Weird idea, but have you thought about some cards that can steal creatures for you regardless of the creature's scale? Sower of Temptation, Callous Oppressor, and Thalakos Deceiver are pretty cheap for what they do. You might also try something like Rite of Replication or Cryptoplasm, copying something like a Blightsteel Colossus can also solve the issue, at least for you.