Despite the fact that Splinter Twin only accounted for around 10% of the Modern metagame, it was the deck you could almost always count on playing against at a given tournament.
More than any other deck, it had a fundamental impact on the type of cards you could play in your deck. Any time your opponent controlled a Steam Vents and two other lands, you had to worry about just dying. This put significant pressure on sorcery-speed spells that cost three or more mana.
Make no mistake, you're still able to die on turn three or four in Modern, but there will be a lot less guesswork in terms of knowing when you're dead now. Burn can kill you on turn four, but you hopefully know your life total at all times. Infect can kill on turn three, but not without an infect creature or Inkmoth Nexus in play when they pass turn. Grishoalbrand is a bit harder to predict, but you either have relevant interaction or you don't, and that deck relies on a lot more going right than Splinter Twin did.
I don't know if you're more or less likely to die on turn four in the new format, but I do know that you're way more likely to know if you could die on the following turn. That is to say that the decision to tap out on turn three will be considerably more informed going forward.
A specific card that hasn't seen much Modern love in some time that stands to gain a lot by this change is Geist of Saint Traft.
Geist was an awkward proposition against Twin, and far too slow against Amulet Bloom. With the proper supporting cast, I could see a significant Geist resurgence in Modern. The deck would presumably be Jeskai colors, which gives you access to white's amazing sideboard cards, the best card in Modern in Snapcaster Mage, and cheap red interaction. Such a deck is my dark horse pick for a strong PT showing.
As far as monetizing this pick, investing in Geist isn't too inviting given the looming Geist duel deck that was spoiled with the Oath of the Gatewatch leaks. But there is some time before that release and a strong PT performance would definitely lead to some short-term growth, at least. I'd look to the supporting cast to find some real winners.
Just like three-mana spells, four-mana spells stand to become more viable in Modern as well. There's a short list of four-mana options for a Geist deck, with Elspeth, Knight-Errant and Ajani Vengeant being exciting options, though these are unlikely to show up as more than one- or two-of type cards. The cards that I would watch more closely are Restoration Angel and Cryptic Command.
Restoration Angel is a card that I picked up a short stack of about a year ago given that it sees some Modern play and is an angel. It has just recently started to see some decent price movement, likely due to its presence in Kiki Chord. Resto has been played alongside Geist plenty of times historically, and Kiki Chord isn't going anywhere.
Seeing as Avacyn Restored was a garbage set, I expect to see even further growth out of this card. The buy-in looks to be around $10 at the time of this writing, which is steep, but if you wait on your play set you'll almost certainly be paying more down the line.
Cryptic Command was pretty much reserved for Twin and Scapeshift prior to the banning, and even still it has held onto a high price tag. With Twin gone, I expect to see more Cryptic Commands.
First of all I think Scapeshift will hold a higher percentage of the metagame. But there will also be more blue decks looking for things to do with four mana, and now you're more able to utilize less efficient interaction without just dying. It's a phenomenal card to use with Snapcaster Mage, and it makes for a powerful tempo play to follow up Geist of Saint Traft. We could also see Blue Moon take a higher share of the Modern metagame.
As a vendor I've found it impossible to keep Lorwyn copies of Cryptic in stock, though players still buy Modern Masters versions. Despite three printings, this card is great in Commander and poised to see increased play in Modern. I wouldn't be surprised to see a healthy price bump over the course of the year. If a Cryptic Command deck or two top-eights the Pro Tour it will happen sooner rather than later.
Blue Moon might sound like an odd choice, but I actually think the deck stands to gain a lot with the banning of Twin. Sure, you lose Bloom as a deck to beat up on, but that was such a rare matchup anyway. What's really important is that you lose the matchup that could combo-kill you easily off of one basic Island. Not to mention that you're one of the better shells for the ol' Bolt-Snap-Bolt, and you are arguably the best positioned deck to kill people with Keranos, God of Storms.
It's true that Blood Moon is kind of a turd against Burn, but even against Affinity and Infect it at least turns off manlands. Generally you need a clock to back up your Blood Moon against Tron, but Cryptic Command can clean up Karn Liberated and Wurmcoil Engine pretty nicely, too.
Blood Moon is a lot better in new Modern than a lot of people are saying it is, and with continued presence in a format increasing in popularity, it certainly has room to grow at least towards its previous high.
Modern as a format is going to continue to see significant growth, and realistically for the more played decks it's less a matter of what or if, and more a matter of when. The Twin ban should serve as a reminder to diversify, though investing in Modern in general remains a strong position.
Anything currently played that hasn't spiked yet is going to see some growth, though in this piece I tried to highlight a fundamental reason why some previously underplayed cards could see substantial growth. If some previously unplayed cards that cost three or four see success at the Modern Pro Tour, then depending on what set they're from you can expect explosive growth in response.
I've outlined some cards here that I like, though there are definitely others that fit this category. These will be the types of cards to watch for at the PT.
Thanks for reading.
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