Monoblack Devotion has been one of the powerhouse decks in Standard since Pro Tour Theros.
Early innovations included a couple of Pack Rats, which became all the Pack Rats; Pack Rats subsequently fell out of favor (and not just in Monoblack Devotion but in other decks where they would seemingly have made more sense). Rats are back.
Another card that has flitted in and out of vogue is Nightveil Specter; biggest, baddest threat not only in Monoblack Devotion but in Monoblue Devotion. The color-intense Nightveil Specter combined card advantage and the fundamental mechanic of the block at hand in a single spell. Though Nightveil Specter is now seemingly out.
But to some degree these kinds of threats flitting in and out of a seventy-five are interchangeable. Nightveil Specter and Lifebane Zombie [main] are kinda sorta the same. Three mana; evasion; card advantage sometimes.
...but some of the more recent innovations to the archetype have been anything but interchangeable.
Tamas Glied made a fundamental change to Monoblack Devotion: it's no longer mono-anything. With the inclusion of Ashiok, Nightmare Weaver to the main deck and sideboard, plus Notion Thief to the sideboard, this deck -- though all the cards are black -- is a black/blue deck in a way that it never really was with Nightveil Specter.
Separately, I've always thought Ashiok, Nightmare Weaver was one of the sweetest threats in Standard; it has seen play in Esper as well as multicolor green decks. But I think it is better in “Mono”black Devotion than anywhere else we've seen it thus far. It is a legitimate way for this strategy to beat control decks; especially as getting by one permission spell or Detention Sphere is fairly trivial with the help of Thoughtseize. With black's many point removal spells, its ability to borrow huge opposing threats makes for some good Magic: The Gathering when facing dedicated creature threat decks, of course.
All-around awesome and a legitimate shift for Monoblack Devotion.
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