One place that people are starting with Pioneer is looking to port over and upgrade decks that dominated old Standard formats. Mono Black Devotion built around Gray Merchant of Asphodel is one such deck that has the potential to make the jump.
Mono Black Devotion Decklist (Pioneer)
4 Thoughtseize 4 Gifted Aetherborn 4 Brain Maggot 4 Kitesail Freebooter 1 Yarok's Fenlurker 2 Nightveil Specter 3 Liliana, the Last Hope 1 Whip of Erebos 4 Murderous Rider/Swift End 1 Dark Prophecy 4 Ravenous Chupacabra 4 Gray Merchant of Asphodel 3 Castle Locthwain 2 Nykthos, Shrine to Nyx 19 Swamp (339)
Gray Merchant of Asphodel is absolutely the main reason to play this strategy. While devotion decks of other colors have to focus entirely on their devotion strategy or they fall apart, black is able to play a lot of interactive cards that contribute devotion count to the board. Gray Merchant then does a great job of draining the opponent out, turning the corner very quickly. Even in a pinch, it provides a ton of life gain which can be all that a controlling midrange deck needs to survive.
Murderous Rider is a great example of a new card that can slot in perfectly to this older archetype. The Standard version of mono black devotion ran Hero's Downfall as a 4-of staple, and Murderous Rider is simply much better. The ability to cast your removal spell as a 2/3 lifelink body is decent in other decks, but here it means we can play some hard removal spells and still have a very high density of permanents that contribute to devotion.
We've opted to go with an extremely interactive take with this build of mono black. We're certainly not the fastest deck around, which means we have to be able to stop our opponent (or at least slow them down). Brain Maggot, Kitesail Freebooter, and Yarok's Fenlurker combine with one of the best spells in the format in Thoughtseize to ensure that we can rip our opponent's hand apart before they get to do anything with it. These discard type of creatures just need to disrupt our opponent long enough for us to enact our gameplan, but having such a critical mass of them often means that they will actually get to stick around on the battlefield and permanently end our opponent's hopes for their cards while contributing to our own devotion count.
Gifted Aetherborn looks like our best bet for another 2-drop that provides double devotion. It blocks and races well against any deck playing small creatures, and it survives most of the cheap burn spells in the format while also being able to trade up for bigger green creatures. We could also consider trying Relentless Dead if we wanted to go for more of a zombie package, perhaps including Cryptbreaker or Stitcher's Supplier with some graveyard synergies.
We haven't yet decided if we actually like Ravenous Chupacabra in this format, but it's the exact kind of effect that this deck is hoping to play. It helps us control the board while grinding out an incremental advantage, and sticks around with some black mana symbols in case we ever happen to draw a copy of our best card.
Liliana, the Last Hope contributes greatly to this deck's strategy. Her +1 ability is excellent against many opponents, and at least slows them down if it's not able to kill anything. The -2 ability can be great when we are running such a toolbox of interactive creatures, letting us get back a discard, removal, or another casting of Gray Merchant. Her ultimate is a great threat as well if we need to find an alternative win condition when Gray Merchant hides near the bottom of our deck.
We've rounded out the deck with a smattering of interesting permanents that are good for devotion that we would like to playtest more. Nightveil Specter was common in the Standard version, and as long as the format's not too hostile to it it still represents a "must kill" threat that can take over a game. Dark Prophecy is likely too cute, but has potential as a strong card advantage engine with strong devotion synergy. Whip of Erebos is a suprisingly effective option given that most of our creatures have enters the battlefield effects. It doesn't necessarily work great with the temporary discard creatures, but being able to double up on any Gray Merchant that we've drawn is usually going to be good enough.
This isn't a devotion deck that craves the mana from Nykthos, Shrine to Nyx like our Leyline of Abundance deck, but it's still worth including a few copies if it won't hurt our mana since the upside can be massive. However, we also have Castle Locthwain to consider, so we don't want to run too many non-Swamps unless they are providing real value. This deck is capable of gaining a lot of life, so the downside associated with Castle Locthwain can often be negated.
As you can tell, we still think this list needs some tuning, though this is partially because a deck like this needs to be reactive to the specific metagame that it is up against. We think the idea of playing powerful synergies mixed with strong disruption is a good way to go in most formats, so we'll be continuing to work on this deck as the format evolves.