Defile looks at all Swamps you control, not just Snow-Covered Swamps. I think you're underrating the card compared to Tragic Slip, though. Slip is obviously much better in your deck than in mine, but I would think there are times where Morbid can't be triggered so the Slip is insufficient. Defile has a longer ramp up but should be able to keep reasonable pace with the toughness of problematic creatures like Gaddock Teeg or Anafenza the Foremost.
It's fairly slow since you have to tap it to add counters and to remove stuff, but I believe your patience will be rewarded. The biggest thing it has going for it to me is that it's a land and therefore has a very low opportunity cost for running it. Having an additional out to Rest in Piece for you or Aura Shards for me with a land that might otherwise be something like Reliquary Tower or a basic is my kind of value. At worst, it's a Wastes, at best, it enables wins by taking out whatever is holding you back.
As for which counters to let it sit at, I think it might be best to let it sit in play with just the single counter or maybe two until a threat presents itself. If someone has something dumb and mildly expensive out like True Conviction or Caged Sun it's likely the mid to late game where it's very possible you're able to produce the 10 mana needed to add enough counters to then untap and blow them up. If they have Omniscience you've probably already lost, and if it's cheap it's trivial to load up and destroy it.
What's your opinion on Blast Zone? My jaw dropped when it was spoiled. Giving mono-black a way to deal with, well, just about any problematic permanent with the potential for a lot of fun collateral damage on a land seems incredible to me even if it's mana-intensive. Still, MBC is known for generating oodles of mana, so the XX is less intimidating than it is for other decks. It doesn't even come into play tapped! I'm having trouble deciding what to cut for it, but that's a great problem to have.
Which lands do you think are bad currently in the list? I have three guesses at the moment, but you might be thinking of more/others.
I don't think you have enough artifacts to reasonably support Inventors' Fair (it also sounds too pleasant and optimistic for the flavor of the deck) and Buried Ruins's target pool is pretty low, though I suppose it does get back your combo altars and is redundancy for Yawgmoth's Will for that. What do you usually name with Cavern of Souls? It seems like you don't have enough consistent targets to make it tap for black enough. Maybe it's useful for pushing through one or two important critters and then you're fine with it only producing colorless. I want to criticize Homeward Path but I do like the idea of reanimating something and giving it back to its owner... for a price, so I'll leave it be. I'm also skeptical of Crypt of Agadeem but with your creature density it probably works okay for you.
I did overestimate the number of doublers you run, though, so feel free to ignore all of the above. It looks like your loops are self-contained and don't require boatloads of mana so it seems less critical for you to go the typical big mana black route.
Otherwise I think your list looks like a lot of fun and I appreciate the balance of flavor/functionality. Also, +rep for the Dio reference.
With adding more discard or more opponent creature death, Sangromancer starts looking like it could do some work. It didn't make the cut this last build because it rarely did much for me before with only one discard source and 1-2 wipes.
Blanket of Night as a backup Urborg. Would also help Sheoldred connect.
Cards I'm unsure of keeping (haven't had a chance to test them in a game yet):
Warping Wail could leave until I have a known need to stop sorceries. Withering Boon has been great, so I don't want to cut that. Not sure how much need there is for Imp's Mischief for redirecting a target or countering a Counterspell, but I've been hoping it'll be useful. Redirecting a kicked Rite of Replication is always funny.
Mesmeric Fiend is very on-flavor, but I'm unsure yet how useful he is to picking apart opponent's hands.
Tortured Existence seemed an interesting way to hide a surprise in my hand for reanimation, though I haven't figure out how it could be part of a loop the way Phyrexian Reclamation can. Rings turns it into a discard version of Victimize, though.
Sadistic Hypnotist over the Myojin for sure, since it's way more on theme both flavor wise and mechanics wise. I'd replace the Mesmeric Fiend for it since it's low impact.
I didn't like Sangromancer. It does generate a lot of life in the right circumstances but I found it to be low impact overall. If it worked for your own creatures it would be a different story, obviously.
I love Warping Wail in my Daretti list, but here I think it forces you to run bad lands in order to support it. You want as many Swamps on board as possible to fuel your doublers, so the opportunity cost just isn't worth it in my opinion.
re: Infernal Tribute vs. Vampiric Rites: I think Rites is by far the better pick here, as the life gain is more relevant than having higher devotion and being able to sac Cabal Coffers to Tribute so you can recur it with Crucible of Worlds/Petrified Field for two activations. Tribute does have the better art, though.
[Primer] Erebos, God of the Dead
HONK HONK
As for which counters to let it sit at, I think it might be best to let it sit in play with just the single counter or maybe two until a threat presents itself. If someone has something dumb and mildly expensive out like True Conviction or Caged Sun it's likely the mid to late game where it's very possible you're able to produce the 10 mana needed to add enough counters to then untap and blow them up. If they have Omniscience you've probably already lost, and if it's cheap it's trivial to load up and destroy it.
[Primer] Erebos, God of the Dead
HONK HONK
[Primer] Erebos, God of the Dead
HONK HONK
I don't think you have enough artifacts to reasonably support Inventors' Fair (it also sounds too pleasant and optimistic for the flavor of the deck) and Buried Ruins's target pool is pretty low, though I suppose it does get back your combo altars and is redundancy for Yawgmoth's Will for that. What do you usually name with Cavern of Souls? It seems like you don't have enough consistent targets to make it tap for black enough. Maybe it's useful for pushing through one or two important critters and then you're fine with it only producing colorless. I want to criticize Homeward Path but I do like the idea of reanimating something and giving it back to its owner... for a price, so I'll leave it be. I'm also skeptical of Crypt of Agadeem but with your creature density it probably works okay for you.
I did overestimate the number of doublers you run, though, so feel free to ignore all of the above. It looks like your loops are self-contained and don't require boatloads of mana so it seems less critical for you to go the typical big mana black route.
Otherwise I think your list looks like a lot of fun and I appreciate the balance of flavor/functionality. Also, +rep for the Dio reference.
[Primer] Erebos, God of the Dead
HONK HONK
re: Infernal Tribute vs. Vampiric Rites: I think Rites is by far the better pick here, as the life gain is more relevant than having higher devotion and being able to sac Cabal Coffers to Tribute so you can recur it with Crucible of Worlds/Petrified Field for two activations. Tribute does have the better art, though.
[Primer] Erebos, God of the Dead
HONK HONK