Black currently has 24 creatures and the curve is a bit awkward. However, fixing it might be hard, because there are creatures with Delve in the cube. Black’s thing is removal, so the cube probably needs some of that. Probably some that can deal with gods as well as cheaper, easier to use stuff.
Creatures
The current curve is as follows: 10 / 2 / 6 / 2 / 2 / 1 / 0 / 0 / 1, that nine being [scryfall]Necropolis Fiend[/scryfall], so its more like a five- or six-drop.
The curve right now is very strongly centered on one-drops, which is a bit of a problem. I was hoping for a bit smoother curve at this point. On the other hand, many of those one-drops are more about a longer game than initial aggression. Here’s the list:
Sure, some are very aggressive, but others have a completely different roles as removal, sac outlets and discard. You can still utilize these in an extremely aggressive deck, though, even if they are inferior to white and red alternatives.
Supposing I want to put in eight more creatures (making the total 32), I’d want to put in five or so two-drops, two four-drops and one five-drop. That would leave me with the curve of 10 / 7 / 6 / 4 / 3 / 1 / 0 / 0 / 1. Sounds about right.
Do I dare put in [scryfall]Blood Artist[/scryfall]? I think not, so I’ll skip for now.
[scryfall]Blood Scrivener[/scryfall] isn’t as good, but the card advantage can do some work for you.
[scryfall]Carrier Thrall[/scryfall] can be some good value, as can [scryfall]Sultai Emissary[/scryfall].
[scryfall]Despoiler of Souls[/scryfall] is a good addition, if you want to play the more aggressive build of black.
I’ve enjoyed [scryfall]Gatekeeper of Malakir[/scryfall] in Modern, so I guess its fine here.
Finally, [scryfall]Mardu Skullhunter[/scryfall] is good value, I’ve played somewhat in Standard.
Do I want [scryfall]Desecration Demon[/scryfall] in the cube? I’ll try it.
I’ll put in [scryfall]Disciple of Bolas[/scryfall]. The body isn’t great, but its a good addition the cube, since its effect can vary a lot.
Finally, [scryfall]Gilt-Leaf Winnower[/scryfall]. I haven’t checked the number of creatures it hits, but a quick glance tells me it mostly gets rid of fairly small creatures, so its not going to be an absolute bomb. Just a bomb.
Removal
Well, its black. These shouldn’t be hard to find.
First, [scryfall]Go for the Throat[/scryfall] is great piece of removal. It hits pretty much anything. Well, not the gods, but everything else. [scryfall]Doom Blade[/scryfall], [scryfall]Terror[/scryfall] and [scryfall]Ultimate Price[/scryfall] are kind of from the same family, but in this environment they are worse.
[scryfall]Consuming Vapors[/scryfall] is a nice edict. Its pretty expensive, but the incidental lifegain might matter, depending on what you are playing against.
[scryfall]Gild[/scryfall] works nicely in this environment, as does [scryfall]Silence the Believers[/scryfall].
Another killer of gods is [scryfall]Tragic Slip[/scryfall]. Got to love that one.
[scryfall]Despise[/scryfall] isn’t removal, but does the same thing.
… and we need a sweeper. [scryfall]Damnation[/scryfall] is out of the question, [scryfall]Crux of Fate[/scryfall] doesn’t seem very good in an environment with a limited number of dragons. I guess [scryfall]Life’s Finale[/scryfall]? We’ll go with that, although there are might be better options. It is sort of an answer to gods.
Others
Sadly, that leaves room for just one more card. After going through some cards and not coming up with anything interesting, I think I’d like [scryfall]Unnatural Endurance[/scryfall]. Its a very good trick and obviously pushed, so it should fit in a cube.