The whole of Dominaria United has been spoiled, and it's looking to be a solid set. I'm not damning it with faint praise, I'm being serious. Nothing looks too powerful, nor is the set particularly weak. A good solid power level with interesting but not overwhelming cards. Just like our last trip to Dominaria. Of course, that was quickly followed by a series of severe design mistakes. I hope that won't be the case this time.
In terms of Modern pickups, the story is similar. There are a number of solid role players but nothing stands out as format-redefining. A number of decks will receive interesting alternative tools and there are plenty of almost-there tools to consider. Then there are the tribal lords. This cycle of two-mana lords will actually have a substantial impact on Modern. How substantial and sustained is unknown, but they'll absolutely see play in the immediate future.
The Other Guys
Well, most of them will, anyway. The black and white lords will not see play in Modern. Being lords for less-supported tribes is a huge strike against them. Valiant Veteran is close since most of the best humans are also soldiers, but not close enough. If Enlistment Officer were legal it'd be another story. The extra power and toughness are nice, but the five-mana activated abilities are the final straw. There are cheaper and faster ways to do what they're doing. However, the other colors' lords are absolutely playable.
Of them, the most obviously good lord is for goblins. Naturally, Rundvelt Hordemaster has generated considerable interest already, so I won't reiterate others' points. Hordemaster is (potentially) a huge pickup for goblins and as a card advantage engine, it could get quite busted alongside Skirk Prospector.
However, one thing I haven't seen others discuss is whether or not Hordemaster actually adds anything to current Goblins lists. It's just assumed that it does because obviously. To which I ask, "is it actually obvious?" Modern Goblins is primarily a combo deck. Most versions intend to win via Conspicuous Snoop and Bogart Harbinger. They're already using Goblin Matron and Goblin Ringleader to make it happen, and Hordemaster needs four goblins to die to hit like Ringleader. At that point, it isn't actually card advantage.
I'm not saying Hordemaster is unplayable. Rather, I don't think just slotting it into existing decks will work. They're not looking to make use of the +1/+1 part because they're not meant to win via beatdown. They have the tools to dig for the combo already. To really make use of Hordemaster will require some retooling. A Food Chain that sacrifices being printed would also work.
The green lord hasn't been getting much press, but it is quite similar to Hordemaster. Leaf-Crowned Visionary is another lordly card advantage engine. However, this time it's a mana payment on freshly cast creatures. This means that the new Visionary is the closest Modern Elves has to the banned Glimpse of Nature, an incredibly busted card.
Modern Elves has suffered more than other tribal decks in recent years. The problem is that the individual elves in the deck aren't very impressive. Despite contributing to a Legacy-defining mana engine, the individual elves are so dorky that the whole deck can be derailed with a few removal spells. Legacy Elves gets around this with better tutors and also Glimpse to combo-win more consistently. It also has Gaea's Cradle where Modern must make do with Elvish Archdruid.
While Visionary is inefficient compared to Glimpse, it's still quite strong. The Nettle Sentinel/Heritage Druid duo is in Modern and can generate the mana needed to draw through the deck. With an active Archdruid or just enough cheap elves making extra mana, the Craterhoof Behemoth kill is much more plausible than ever before. Which might be good enough.
The Card I Care About
All that's perfectly fine and everything. However, it's the blue lord that I'm actually excited about. It's a merfolk lord, and I have a history. Yes, for the first time since Merfolk Trickster, a Standard-legal set has printed a Modern-playable merfolk. Vodalian Hexcatcher is quite the card. Hopefully, it will lead Merfolk to the glory that I and many other fishionados have said it deserves over the years, but it will definitely bring many players into the school.
While Merfolk already has many lords, another one is always A Big Deal because Merfolk is the lords deck. The Humans deck uses counters, not lordly buffs, and I've covered Goblins and Elves. Spirits is the only other deck with lords, but their best one is three mana. Merfolk is all about the two mana lords, and the new one adds to the overall strategy while protecting against a major antagonist.
The biggest problem cited for the fall of tribal decks over the past year is Fury. A maindeck sweeper is always going to be difficult for tribal decks to overcome, especially when attached to a creature. This is partially true, but not for the expected reasons. Fury is rarely more than a two-for-two against smart tribal players, which isn't great. The problem is that evoking Fury is a huge tempo gain, and that's usually the devastating part. Clear my threats and add to your own strategy, great turn, gg no re.
Hexcatcher stands to make that a much harder sequence. Flash means that Hexcatcher can save the creatures targeted by Fury without an Aether Vial, unlike the other lords. This can require the opponent to play additional removal (or Ephemerate) to finish the job, which takes away the tempo gain. Add in that Hexcatcher can sacrifice the merfolk that would die and potentially counter the removal, and suddenly the matchup looks pretty solid.
Adding to the Package
That last point is also more generally salient. Merfolk was the original disruptive aggro deck. In recent years that crown has been taken up by Humans and Spirits, thanks to cards like Kitesail Freebooter, Mausoleum Wanderer, and Spell Queller. Prior to Hexcatcher, the best new disruptive merfolk has been...Tide Shaper, I guess? Hexcatcher turns every merfolk into a better Cursecatcher, which is a considerable upgrade.
I also just realized Hexcatcher is a direct callback to Cursecatcher. Neat.
Force Spikeing every non-creature, non-Supreme Verdict card in Modern is quite good, but there is an additional benefit. Even if Hexcatcher fails to counter it, Hexcatcher is still answering Living End. So much of the value of Living End is in sweeping the board, but Hexcatcher fills the graveyard. Countering the current Living End and, as a bonus, ensuring that a later one isn't devastating is quite good. Remember, Hexcatcher has flash and should be used as a surprise.
Making it Fit
Vodalian Hexcatcher is 100% Modern playable. The question is how to make it fit. Most Merfolk players have settled onto a common maindeck strategy, and I've been going along with the trends. I mostly play Burn these days due to metagame considerations, so I just follow what the more dedicated players have determined when I want to get my fins wet.
However, after weeks of mediocre FNM performances and tuning the deck to be an anti-cascade specialist, I have problems with some of the mainstream card choices.
There have been times when Phantasmal Image was an integral piece of Merfolk. Copying lords is good, and sometimes copying opposing creatures is better. That pedigree helped Glasspool Mimic // Glasspool Shore gain traction, especially since it's been used to skimp on actual lands.
However, I've been consistently frustrated by Mimic. I've had to mulligan an alarming number of hands thanks to Mimic being my only creature. Drawing it late game with no creatures out (remember: Mimic can only copy your own creatures) is often devastating. However, Mimic is kind of necessary thanks to the other two cards on my list.
Force of Negation
I know it sounds weird, but I've really soured on Force of Negation. Free interaction is quite good. However, Force of Negation is no Force of Will. Non-creature spells are seeing less play thanks to the evoke-elementals, especially the interactive spells that Merfolk actually wants to counter. Worse, Force is quite bad at countering a particular group of non-creature spells.
I've lost to cascade decks many times because Force cannot be cast for free on my own turn. Violent Outburst is quite the card and getting cascaded on in my upkeep turn three hurts. It's why I've started running Cursecatchers again. Pitching to Force is, admittedly, a good use of Mimic, but it's such a feel bad that I'm looking for alternatives.
Force's limitations may be why Subtlety has been adopted. It isn't limited by turn and hits what Force misses. I will admit that when Subtlety is good, it's very good. However, it is only good in very specific situations. The primary one is against other evoked elementals. There's something viscerally satisfying in making an opponent exile two cards and spend a draw step to Fury your board. The other is against Amulet Titan. Hitting Primeval Titan is good, but I've also won by using Subtlety on Azusa, Lost but Seeking after my opponent Summoner's Pacted for her with only two lands.
However, in every other circumstance, evoking Subtlety is mediocre. If I'm feeling generous, anyway. A 3/3 for four flyer isn't a good rate. Using Subtlety on more normal creatures or planeswalkers is just kicking the can down the road. Yes, hitting Murktide Regent is good, but drawing Subtlety after it comes down is terrible. The floor is so low it really doesn't justify the ceiling in my experience.
What I'd Do
With those complaints, off my chest, when Vodalian Hexcatcher is legal, I will be playing this maindeck, which I'm currently testing:
I'm going to replace the Forces with Hexcatcher, which do effectively the same job without ever being a dead or frustrating-to-cast card. Subtlety is getting dropped too, and right now I'm testing the never-was Rishadan Dockhand. Tide Shaper completely stole Dockhand's thunder, and I've never really tried it out. I have frequently wanted more disruption and one-drops, so Dockhand is a good fit. It hasn't been terrible in testing so far.
With the pitch cards gone, I can cut the Mimics and just run lands instead. In particular, I'm going to a full set of Cavern of Souls. Again, removing the pitch spells makes this a better choice than before. More importantly, it plays well with the full set of Chalice I'm running. I've been doing that now and been quite happy, so I expect it to still be a good option in the new Modern. The sideboard will depend on what's doing well once the new cards come in.
Fish Swim Together
I'm looking forward to getting back into Merfolk again. Whether I'm able to justify staying in the school will depend on how the metagame shakes out and whether Hexcatcher works out as well as I expect. I'm hopeful but experienced enough to temper those expectations. We'll all see soon.