Gotcha!
It's looking like the best support colour right now. Black needed a couple of things it got, and one thing it got which no other colour in the control archetype had. Those were:
Fatal Push - Dreadnought cheese? Dead. Pumped Longtusk Cub? Dead. Copter? Dead. Heart? Dead. Manlands? Dead. High toughness tokens? Dead. Any other 2cmc creature you care to mention in aggro decks? DEAD! Black needed splashable aggro removal at instant speed, we got it at uncommon. Revolt for this is easier to trigger in less control based builds, but you'd be hard pressed to find a reason to not run this in any Black deck.
Herald of Anguish - Whilst more narrow than I'd have liked, Black finally has a GOOD demon finisher (Kothophed crying noises). He won't be that efficient for 7 mana outside of artifact decks, but he will excel in those and "heralds" a change in Black's good creatures all being the lower costing ones.
Yahenni's Expertise - Wait, this sweeper is worse than Languish. It's one whole less damage! Oh, except that it lets you free cast a Dynavolt Tower or Liliana in control, a whole slew of artifacts in Tezzeret decks, and replace any board presence you lost in Midrange decks. As far as sweepers go, this negates one of the big disadvantages of tapping out on curve to wipe the board: Leaving yourself at the mercy of your opponent's next turn with no response.
We're still lacking hand hate, which is probably about as likely as us getting Negate at this point, and I'd much rather prefer a more open-ended demon finisher, but we're at a point now where Black no longer sucks! It's still not quite the colour that can dominate in builds where it's mixed with other colours, but it's surpassed Red as the best supporting colour in my eyes. Now, if only Blue was a good colour outside of Artifacts decks or drawing cards...
received though. 
I can see the argument for running it in midrange aswell as an early blocker.
