I hate to be a bother, but...

Relevant from gatherer: If a creature returned to the battlefield with unearth would leave the battlefield for any reason, it's exiled instead -- unless the spell or ability that's causing the creature to leave the battlefield is actually trying to exile it! In that case, it succeeds at exiling it. If it later returns the creature card to the battlefield (as Oblivion Ring or Flickerwisp might, for example), the creature card will return to the battlefield as a new object with no relation to its previous existence. The unearth effect will no longer apply to it.

Other than that final mini combo not working, this deck is pretty neat. I think the damage will... rack up... quickly enough that you wouldn't have many problems unless they happen to be playing red deck wins or some other fast combo. I really think this deck would also do well as mono black. +1 all the same.

That's unfortunate that I can't rescue unearthed creatures. I got away with it in casual play. I figured it must not work for some reason, because someone else would have been using the trick already.

This deck actually started in mono-black, but let's look at what I lose.

First, I lose Sedaxris Specter. Shimian Specter and Guul Draz Specter are potential replacements, but they're 4CMC instead of 3CMC for 2/2 instead of 3/2, and without the unearth ability that is consistently reliable for another discard + 3 damage, which is huge (even without the bounce-stunt). Needle Specter is a 3 CMC option, but it's 1/1 instead of 3/2. (Shimian Specter is probably what I'd run in its place.)

Second, Augermage is also out. There's simply nothing remotely close to it in mono-black except for Nezumi Shortfang, which I'm already running a playset of. (Guul Draz Specter is probably what I would run in its place.)

Third, I lose Piracy Charm , which has a lot of versatility, especially considering that almost everyone will have an island on the board, so Islandwalk = Unblockable. But I'd probably run Disfigure in its place, or perhaps Oona's Gatewarden .

Fourth, I lose Dreadbore , but that could be replaced with Go for the Throat or Doom Blade . Those are more fragile and can't take out a planeswalker, and diverting damage to a planeswalker removes the pressure on their hand. I could do Hero's Downfall for the planeswalker hate, but that's 3 CMC instead of 2 CMC.

So mono-black is significantly slower while also being less versatile, at least insofar as I can see. I'd be interested in seeing what you could do up.

I'd like to lead with the fact that I'm not saying mono-black would be better, but just that it would work well.

For your Specter, I wouldn't recommend either Specter you mentioned, but if unearth is your preference, maybe Rotting Rats suits well, though it pains you a bit as well. I also don't think Ravenous Rats is a bad choice, but you were clearly after ninjutsu jumps... but I see that card is gone now and replaced with Ghastlord... probably a good call overall. Was going to recommend Slate Street Ruffian or Stronghold Rats for that. I also like Abyssal Nocturnus in general.

Piracy Charm is admittedly pretty great... It's just so versatile. But if it were going to be mono-black, there are tons of options, from the overused Thoughtseize to Duress , Inquisition of Kozilek , or many others. My personal favorites for modern are Cry of Contrition and Raven's Crime , with Horrifying Revelation at a close third. Also, another direction might be Dream Salvage , but that looses viability in the mid- to late-game.

Rakdos Augermage's repeatable discard is nice, but not instant speed nice like shortfang. However, there are still some good adds in it's place. Dimir Guildmage comes to mind. it's ability is pricey, but good later... admittedly, that isn't when it's most useful, but at least it doesn't require you to discard. Augur of Skulls is a great blocker, as you can regen him if needed then pop him once you own the field. Thrull Surgeon is ok, but doesn't chump like Black Cat and Drainpipe Vermin , which may discourage attackers as a bonus for early game. Nezumi Bone-Reader is another good option. Last, more no card damage in Quest for the Nihil Stone .

Anyways, if running to mono-black, I think the Hero's Downfall is quite affordable, but regardless, you're playing control, so they shouldn't be getting to play much, and I think the planeswalker won't take too much work, especially if they're down to 0 cards in hand, just hit it with the ghastlord or stronghold rats. Then just run a 2 cost creature kill. I was under the assumption that the wincon is the multitudes of no hand pain. once you get there, you kind-of just have to wait.

Only 10 of your 22 lands are not slow, so in reality, this deck will start a fair bit slower than mono-black with a few one cmc higher cards. I think quicker lands would be much better but can be quite costly. Also, cutting it back to U/B or B/R will pick up your mana pacing too. And if someone wanted, this could become a rats/rack deck fairly readily. It's a great concept with a lot of versatile options for builds.

Cards that act as blocks or discouraging attacks don't work with this deck. The whole theory is that the creatures themselves are doing damage. If the creatures aren't doing damage, you can accomplish whatever they are doing for easier in other ways.

I looked at Slate Street Ruffian , but you're at a 3 CMC with nothing making it easier to get damage through (flying) and a 2 toughness body, so you're probably looking at a 1/1 trade there. You'd be better off with a straight up discard card (Wrench Mind ).

I've found Quest for the Nihil Stone , like Bloodchief Ascension , to be really slow. Simply too many conditionals to get it to fire. Thrull Surgeon is simply too mana expensive for the pay-off. Abyssal Nocturnus pumps at the wrong time for this deck, since dealing combat damage kicks off the discard. It's also got no synergy with Ghastlord of Fugue .

(Bloodchief Ascension is useful against burn, however...assuming you survive long enough. Short of Leyline of Sanctity , I'm not sure how else to handle burn.)

That said, Augur of Skulls is a very strong contender: I should have remembered him when discussing the mono-black approach. It's straight discard with bonus chump block, with no straight damage...but it'd work. Black Cat and Drainpipe Vermin might discourage attacks early in the game, but they're expensive and ultimately a 1-1 in terms of cards, with versatility and little chance of doing damage, so they're out.

I'd not seen Stronghold Rats , but that's practically made for the mono-black variant of this deck.

Cry of Contrition would work well in this deck, in that it'd set up discard-if-you-do/discard-if-you-don't double binds. And it would pop automatically with Augur of Skulls .

Replacing a creature with Cry of Contrition probably isn't good, though... In playing between this, vanilla 8-Rack, and 8Rakdos, I've found that you really want to use many instants or sorceries, then you have to go creatureless. As normal 8-Rack and 8Rakdos play out, the opponent is probably sitting there with creature removal and no targets to hit. Running just a few creatures means that you're effectively doing a 1-for-1 discard, but those are cheaper to do than 2 CMC creatures. (I don't run Bob, for instance, because he dies immediately to removal.) In creatureless 8-Rack/8Rakdos, you end up with those removal spells being buffers that ease the pain of discard. That buys your opponent time, but at the cost of dead draws. So I was trying to go the other direction, and see if I could draw the removal and still push through creature damage.

Another problem that discard decks have (which I'm trying to solve) is that aggro will often get their creatures onto the field ASAP, before the control really has time to take. Ur-Delver is the classic example of this. Running the 8-of charms gave me the +2/-1 in order to wipe out those utility creatures that make things truly obnoxious later on, with Dreadbore being plan B. This is why I was concerned about the 3 mana: if I have to wait until turn 3 to do creature removal against an aggro deck, I'm sunk. If I have to bank on being able to discard their aggro threats before they can play them, I'm sunk. Hence running Disfigure in its place: that would still allow me to wipe out their utility creatures.

The mono-black approach is really interesting, though. I could probably reduce the overall number of lands and add in some more creatures, too...especially if they were cheap. But Sedraxis Specter and Rakdos Augermage are so good and do so much damage...I'll miss them.

BTW, I'm also very open to feedback on the mana base. The fetchland/painland combo was literally killing me, which is why I modified to where I'm at. But it is slow.

Oona's Prowler is actually a strong possibility for the mono-black version. It's usually used as a discard engine for madness decks, but a two-drop that forces the player to decide between discarding a card and taking 2 damage is something to consider. It would work as a kind of proto-specter. I'm usually opposed to giving the opponent choices, but it being a 2-drop vs a 3-drop is a pretty strong argument in its favor.

Mindslicer is another alternative to running a 4 CMC specter in the mono-black version. It works to keep the pressure on the damage front with the threat of totally emptying the hand if you kill it. (It's a kind of Phyrexian Obliterator for 8-Rack.)

And, of course, there's always Descent into Madness to consider...

Like I said, your build is very good and I don't really have suggestions, I just think there are good options in mono-black, U/R, and R/B as well as the original U/B/R. Also, I'm seeing the deck as more direct damage wincon, whereas you're going for joint creature damage as well. Nyxathid might not be bad for your mono black version. And an Urborg, Tomb of Yawgmoth means funeral charm lets him walk in.

The racks are more a way to seal the deal and enhance the control aspect of the deck. In order for the racks to be worth anything, though, there needs to be constant pressure on the oppnent's hand size, which means the creatures should generate discard (and preferably card advantage). The goal with this deck is to create threats that they have to respond to (evasive creatures vs. a rather open board), but then to limit the potential options (discard) and punish them for responding to the threats (racks).

And it works! I do think this version works about 2-3 turns faster.

Yeah, that's my experience. As much fun as Rakdos Augermage is, the mono-black form is straight up faster.

Still tempted to swap the Shimian Specter for Stronghold Rats , just so that I'm not putting all my eggs in the "flying" basket. Plus, it's a mana faster. On the other hand, it's a mutual hit, not a choice, and doesn't nuke the card from existence....which is how Shimian Specter stays in play.

Howltooth Hollow is also a beautiful thing.

Stronghold Rats can also get rid of lands, which is nontrivial, since holding onto lands is a good way to keep your card count up...