The Solution Part 3
With the card-by-card analysis complete, the question becomes how to build the sideboard. As with all well built sideboards, it must be based on a series of plans for dealing with all potential opponents. In this case, the sideboard doesn't contain hate for specific decks because outside the mirror there isn't good hate available. Instead, the goal is to provide the deck with the type of tools it wants against any given opponent.
That starts with additional copies of cards that didn't quite manage to get four slots in the maindeck. Stormscape Apprentice and Exclude are often shaved out of the maindeck to make room for Disrupt or other new cards, and I would say that any copies of Exclude not in the maindeck have to go in the sideboard by default. Stormscape Apprentice is a more difficult case. Before Apocalypse, it was clear that the deck couldn't go without them, but now I can see leaving one out entirely. With any normal sideboard, it will be replaced by a very reasonable card in every matchup. Keep in mind that Disrupt is a universal fill-in, and that the Apprentice is going to be problematic against everything with Fire and Ice. That said, this comes down to whether it can be sacrificed in the two matchups where it will matter: The mirror and against red-green.
In the mirror, Stormscape Apprentice is never going to be bad unless it is caught in an Unnatural Selection trap. That said, Unnatural Selection is the card this matchup revolves around. For those who don't know what the card does, Unnatural Selection's purpose here is to turn two copies of the same card into Legends, which kills whichever was made into a Legend later. In a mirror matchup, that means that there are seven or eight of most of the creatures between the two decks. That makes the chance that there will be a second copy of any creature the opponent plays highly likely, whether that second copy is yours or theirs. If one player has the only Unnatural Selection and it remains on the table, that player suddenly dominates the game. At that point, his job is to avoid trading creatures off as much as possible, since that weakens the effect of the Unnatural Selection. Stormscape Apprentice is vital there, because by locking down an opposing creature it prevents what would otherwise often have to be a trade. With more different creatures on the table, as time goes by, the Selection becomes more and more important. Let it win the game, and it will. This is more than powerful enough to justify sideboarding in Aura Blast to stop the Selection, especially if it is likely to hit Lashknife Barrier as well. As for the Barriers, normally a few will have to go even though they are very good.
The problem is that there's literally nothing that wants to be sideboarded out. Repulse and Exclude can come out if they have to, and the last copy of a few of the less useful creatures like Spectral Lynx and Galina's Knight can be taken out because duplicates are too vulnerable to Unnatural Selection. That minimizes the damage from not having an Apprentice, because it gets replaced by a creature, even though it's not particularly pretty. That allows the deck to sideboard in Gainsay, Unnatural Selection and Disrupt. Disrupt is an odd issue though. When the opponent is almost certainly using Repulse and Exclude in addition to Absorb and Gainsay, playing Disrupt is automatic. If it can only stop Gainsay and Absorb, it's a lot more questionable, and it starts to look like there might be better cards out there. Then again, it can also try and stop Aura Blast, especially if there's a counter war over it. My instinct right now is to leave some Disrupts in the deck because they help in the fights over Unnatural Selection. The reason I'm avoiding giving a specific prescription is that there is too much of a guessing game element here. Any known set of cards in and cards out would be a target. Instead, what the players are doing is really creating a new build of the deck from scratch before each game, and that build is heavily influenced by such elements as what the opponent is likely to do and name with Meddling Mage, how many Unnatural Selections they have available (or what their mirror card is if it is different) and who is going first. Rarely will the setup for game two be the same as before game three, and if it is it is vital to pretend to resideboard to keep the opponent on his toes.
Against red-green, things are a lot more straightforward. The ideal setup is to have four each of Lashknife Barrier, the twenty creatures in the base, Repulse, Exclude and Absorb along with the standard twenty-four lands. The maindeck and sideboard should try and combine to get the deck there. If any of those cards are missing, they have to be made up for in some way. Having a Disrupt or two still in the deck is less than ideal but far from the end of the world. Having a Crimson Acolyte or two is fine, but not a substantial improvement. The conclusion here is that if Stormscape Apprentice is cut, it makes a lot of sense not to sideboard the fourth in and to use a Crimson Acolyte instead to plug the hole in the red-green matchup. Also note that the Acolyte is essentially non-cumulative, so the fewer copies there are the better each one is. I can think of plenty of matchups where I would bring in one or two due to some red removal but I wouldn't want more than that.
A key card vs. red-green
The matchup against control is about going on the offensive from turn two and never letting go. The sideboard has to reinforce that, and it does. Disrupt, Gainsay and Pure Reflection are the tools that keep the early creatures going. Trying to do anything else would require taking out something that shouldn't come out. Given that there are twenty creatures (since even if one or two are missing Acolytes will have to replace them after sideboarding) that leaves sixteen spell slots. Eight of them are Disrupt and Absorb. The most Pure Reflections the deck wants in this situation is three. The third does have a small problem, which is that the deck can't increase its creature count anymore now that Crusading Knight is a bad card. It could simply add Crimson Acolyte to try and compensate, but it's no longer realistic to expect the trick to protect the deck from Void and there are a lot of decks using Nightscape Familiar. So instead, the last few slots are taken up by Lashknife Barriers. That lets the deck deal with Fire and Ice and in multiples with other burn spells in a more permanent fashion and helps contain any random elements that weren't expected. However, this does leave something to be desired. Ideal here would be a few copies of a larger casting cost creature that was useful. Ironically, there just isn't anything. Emblazoned Golem would be ideal if it cost anything other than two, but at a cost of two it just won't work because of Void. That leaves an unlikely candidate: Dodecapod. It's obviously nice if it gets accidentally hit by discard and it's a great sideboard card in other places. Having a 3/3 artifact available is more useful than it sounds. The other choice is to bring back Crimson Acolyte and hold on for dear life. It's incredibly risky, but in many ways it may be better than the alternatives. So the battle over the last two slots in the deck comes down to Lashknife Barrier (which is already available), Dodecapod (which has other uses but needs slots) and Crimson Acolyte (ditto). One could also be the fourth Gainsay, but keep in mind that it doesn't just get automatically sideboarded in against all blue decks.
The bottom line is those two slots have to exist. That goes along with three Gainsay and three Pure Reflection. That's eight, and if the switching of Disrupt into the maindeck just puts new cards into the sideboard that makes ten. Unnatural Selection comes in next, and takes up at least two slots and probably three. If Exclude picks up the last two, that shuts out Aura Blast entirely, although everything else is taken care of. In general, Aura Blast isn't all that important except against Domain. In the Domain matchup, Aura Blast is the best card the deck can have. Sometimes the Domain deck will try taking out Collective Restraint, but that's a really big mistake. Then again, if everyone else has four Aura Blasts, that fear can justify not using them. I always clear room in the sideboard for them, and they never seem to do anything. In addition, a well-built Domain deck should be able to handle the matchup just fine anyway, although the deck definitely has tools to fight with. Naturally, Exclude, Repulse and Lashknife Barrier come out, and Disrupt and Gainsay come in (the normal creature to control battle switch) but there are five more cards to bring in. Given the sideboard that's been selected, this is going to be a problem. It's not impossible that Unnatural Selection could prove useful, but that's basically depending on them to walk into it with token generators. That's not all that great a bet. Pure Reflection isn't bad, but it doesn't really add anything to the deck. Then again, neither did the cards coming out. The plan is to stop the few cards in Domain that can deal with the attack, and the last few cards in the Solution going to waste is horrible but not the end of the world. But there's no question, losing Aura Blast really hurts. A few copies of Repulse or Exclude can stay in, on the theory that since they should obviously come out. An Exclude will be unexpected and they'll play into it. On the other hand, Repulse is a little less risky. It's a balancing act. The Solution needs about an 18 card sideboard to be able to do everything it needs to do, and about 21 to do whatever it wants to do. Right now, sacrificing against Domain makes a lot of sense, since it keeps refusing to win.
Against the Trenches deck, Pure Reflection comes in and so does Unnatural Selection. That means there's more than enough cards available. In addition, it brings up the fact that together those two rule the battlefield. Unnatural Selection turns creatures into 'Reflections' and then Pure Reflection wipes them out. In addition, the Selection can save old Reflection tokens by making them some other kind of token until end of turn. That's in addition to the Legend ability, which can mow down Trenches tokens or duplicate creatures. No-Mar or Go-Mar decks are basically a variant of the mirror, with the added bonus that versions without more than about ten creatures in them are ripe for the Reflection/Selection combination since they duplicate creatures in the Solution deck. Regardless, the same cards are vulnerable as in the mirror.
The final two matchups are against Questing Phelddagrif decks and against g-r-u. playing against the Questing deck means trying to win quickly, since they will have the tools to win late. Treat them like a control deck. Since the two decks overlap on creatures, Unnatural Selection comes in. One Pure Reflection is possible, as a gambit, since it won't do anything without the combination in play. If the matchup seems bad enough, a second one can even come in to try and steal the win. The question is whether things are really that bad. They're pretty bad if Selection doesn't come out, since they have the long game secured and enough short game weapons to not lose too badly. Sunscape Familiar keeps Lashknife Barrier from getting the attack through, although there are still some bears to fight. Trying to break through with Repulse isn't going to work. There's also the constant danger of Rout after sideboarding. In short, I would take out Repulse and Lashknife Barrier to fit in Unnatural Selection, Gainsay and a few copies of Pure Reflection. This would work better with four copies of Unnatural Selection, but that doesn't make much sense where the combination isn't involved. The metagame is definitely turning against Solution decks. The Apprentices are vital here, a big argument for not touching them. Exclude should stay in in some quantity, since he's going to have to cast creatures to fight with.
The last matchup is g-r-u. This is even worse. Their deck oozes card advantage. Crimson Acolyte is small, doesn't stop that many spells and gets bounced. Without one, Flametongue Kavu goes to town. They can fly over with Gaea's Skyfolk, draw cards with Fact or Fiction, always use their Excludes and make maximum use of Gainsay while all the Solution can do is hope that Gainsay works when it needs to. The variety of colors and threats in their deck makes sideboarding against them difficult. Again I would try for speed in some form, but the question is how. Disrupt and Gainsay are both risky but vital. Exclude is hard to use, but not using it opens things up too much. Then there's Fire/Ice. Just as before, I would take Repulse out of the deck. After that, it's all murky, and I don't really know what the best thing is to do. At least eighteen or hopefully nineteen creatures need to stay in. There's actually a lot to be said for mixing it up among the remaining cards, since the opponent will probably start playing around what they've already seen. Lashknife Barrier is good but keeping in four is probably impossible. Besides, the second one doesn't do all that much here (although the third can be useful indeed).
To conclude, there's a reason this deck was called The Solution, and even though the deck is stronger than the name would indicate, it has definite problems with genuinely new strategies. There's no more room in the sideboard and a distinct lack of good new answers even if there was space. The deck got only one good card out of Apocalypse, and the color diversity of the opposing decks is a major problem. Still, I would consider it a solid choice for a player who likes this type of deck and doesn't want to spend too much time on the format. It's the second logical option after red-green, and red-green is basically a sitting duck at this point for anyone who decides not to lose to it.