Magic Arena was designed with the intention to be Magic's premier competitive showcase, and it's well on its way to achieving that goal – the announcement that 2019 would feature "Mythic Championship" pro-level events hosted on Magic Arena made it clear just how important the program is to Wizards, and that its ascension to pro play is just months away. While Mythic Championships will only apply to a very small number of people, the TwitchRivals event this past Tuesday, which invited 45 popular streamers to compete for $10,000, was just a glimpse into what is possible in the future. There will be tournaments of all sorts, shapes and sizes played on Arena in the future, whether hosted officially by Wizards or privately organized.

Success on Arena means not only learning the software, but also some rather significant changes to the game itself compared to playing Magic Online or paper. The most significant departure from the norm is the starting hand selection algorithm, which selects the best of two random hands, essentially an artificial-intelligence generated free mulligan. Its implications on deckbuilding and mana are significant and difficult to truly understand without digging into the math, and luckily one of Magic's great thinkers tackled the problem.

The new opening hand rule is only applied to best-of-one games, not full best-of-three matches, but this best-of-one format is an important part of Magic Arena. The recent introduction of a constructed ranked ladder system that features this best-of-one format only solidifies this point. Best-of-one poses big questions about the philosophical, strategic, and deckbuilding implications of playing Magic without a sideboard.

In the ranked ladder, matches are one game without sideboard, a major change from the typical best-of-three that we've been using since time immemorial. Wizards received so much feedback after rolling out best-of-one ladder that they made a change and added a best-of-three play option, but its label "traditional play" is a clear sign that Wizards is grooming the player base for its vision of the future, where best-of-one play defines competitive Magic. It makes sense to them, because it simplifies the game and makes it more viewer-friendly. Sideboarding has always been awkward during coverage, as it's a downtime without actual gameplay. Identifying to the audience what cards come in and out is usually clumsily handled, if not completely ignored. Best-of-one allows Wizards to get rid of this sideboarding issue entirely, leaving nothing but gameplay.

The impact of the best-of-one structure on competitive Magic is severe, and I am very curious how it will impact deckbuilding. Sideboards allow decks to adjust to whatever the opponent is doing, allowing for both the removal of cards that are weak in the matchup and the addition of cards that are strong, even cards dedicated for counteracting the opponent's exact strategy. In this sense it also fills the role of a safety valve for the metagame, because if a specific deck or strategy is too powerful or popular, then the opposition can use their sideboards to fight back. It's the kind of thing we see in Modern with Dredge, which unopposed can look unbeatable but in the face of sideboard hate can be completely non-functional. This is part of why many are so outraged about best-of-one, because it would appear to completely ruin Eternal formats. I agree, but I also don't believe Wizards has any intention of applying the rule to Eternal formats. This is a Magic Arena rule for Magic Arena formats, so from here on my points should be taken in the context of Standard. In comparison to Eternal formats, Standard tends to be more fair, with less degenerate strategies in need of direct hosers. Sideboarding is still quite important, but in theory is less important to metagame health than in Eternal formats and will be more likely to adapt and find balance.

There is the fact that Magic Arena is going to feature a "Standard Plus" format after the next Standard rotation, the beginning of a new Magic Arena Eternal format, so the sideboarding issue could be a problem in the future. That said, if best-of-one is the new reality, then cards are being designed with this in mind. Perhaps it's manageable, but it's certainly a big challenge to the developers.

So the question for right now is, how does best-of-one actually impact gameplay and deckbuilding? Today I'll attempt to answer that. I'll expand on the theoretical through the lens of the current Standard format, which not only serves as a good example, but is a pressing issue to solve for anyone grinding the ladder.

Linear (Aggressive and Combo) Decks Benefit

If the most powerful application of the sideboard is using hosers and direct answers to the opponent's strategy, then the removal of sideboarding most benefits strategies that are most vulnerable to these sideboard cards. The most vulnerable decks tend to be those that apply the most linear strategy. These decks put all of their eggs in one basket, making them more vulnerable than decks with multiple angles. I mentioned Dredge as the classic deck that is crushed by sideboard cards, but Standard doesn't typically have such extreme strategies. The closest thing in current Standard is the Izzet Arclight Phoenix deck, which in a best-of-one format won't have to deal with graveyard hosers like sideboard Deathgorge Scavenger or Blood Operative.

Where the idea of linear decks benefiting applies to Standard is not to decks that are linear in a combo sense but simply aggressive decks, which are linear in their sole focus on killing the opponent with creatures. Quite often aggressive decks are favored in game one, but then suffer against loads of creature removal and other effective solutions like lifegain after sideboard. In current Standard, Boros is the perfect example since it will often run roughshod in game one but after sideboard face down sweepers like Golden Demise and Fiery Cannonade that puts its linear creature plan to a halt. Best-of-one leaves opponents without recourse, so I imagine that aggressive decks will perform very well in the ladder.

The most linear deck in Standard is actually Selesnya, which plays an entirely creature-based gameplan. It can snowball into the realm of combo with convoke powering out spells, so it's a classic example of a deck that suffers when the opponent can disrupt it. Best-of-one opponents will be forced to include maindeck sweepers or have no recourse when the Selesnya is firing on all cylinders. Given its power and consistency, it looks like one of the very best places to start for grinding best-of-one on Magic Arena.

Linear decks tend to not sideboard very much because they need a critical mass of cards to enable their strategy, and Selesyna has an unimpressive sideboard anyways, so porting it to best-of-one is really a matter of just copying the main and going to battle. One consideration is adding Knight of Autumn, which is one of its best sideboard cards but is flexible enough to maindeck because it has multiple functions.

Midrange Suffers

Best-of-one structure will change deckbuilding by forcing players to play hoser cards that they otherwise would have left in the sideboard. Cards like Golden Demise and Fiery Cannonade will have to become maindeck staples for decks that relied on them to beat aggro, because otherwise they simply won't have access to them. In theory this sort of compromise does just that and begins to compromise the integrity of decks by forcing them to include cards that may be completely useless against other opponents.

If decks are forced to start maindecking answers to linear strategies, then it means the midrange decks that most rely on their sideboards will suffer. In current Standard, Golgari is the perfect example of a midrange deck that relies on its sideboard, similar to Jund in Modern. As opposed to linear decks like aggro or combo, midrange decks tend to be disadvantaged in game one no matter the opponent, but significantly improve after sideboard because they gain access to great answers. If midrange decks no longer have a sideboard to turn to, they won't find themselves advantaged against anything.

Midrange will be forced to maindeck answers like Duress, which are amazing sideboard cards against control but weak against creature decks, and sweepers like Golden Demise, which offers the opposite. Midrange will have to find a way to straddle the line and beat everything, which it might be able to do with excellent card selection like Brainstorm of Faithless Looting, but that's not really a reality in Standard. Another option is to polarize to one extreme to beat one part of the metagame, which is a huge gambit. It could pay off on the ladder or in the right tournament but won't be consistent against a balanced field.

Midrange decks tend to be unexploitable by the opponent's sideboard and don't suffer against any specific hosers, so opponents have a difficult time catching up. Combined with the strength of their own sideboards, it's why midrange decks are typically the best decks in metagames and have been for years. Best-of-one significantly shakes things up by removing the biggest asset of midrange decks, and it's going to be fascinating to see how they evolve. Since midrange decks won't be able to answer everything, winning the game will become more of a priority so I can envision midrange taking a more aggressive turn so it's better able to close out games.

One of Golgari's great strengths is its deep card pool, so it could have the tools it needs to reinvent itself for a best-of-one world. One strength it could lean on is its graveyard synergies and Undergrowth cards,which gives the deck its own powerful proactive element.

Contemplating Control

I am uncertain about control decks, which are at their heart midrange decks that benefit greatly from their sideboards but can also suffer from hosers. Cards like Duress and Negate are common sideboard cards, as are plenty of other troubling things Carnage Tyrant and Experimental Frenzy. In theory, if midrange is worse then control will be best served to move away from midrange and take a more linear approach. Approach of the Second Sun, for example, is a very linear and proactive way to play control and would have been excellent in a best-of-one environment. Game ones against the deck often seemed hopeless, but bringing in cards like Duress and Negate made a joke of the seven-mana sorcery. I can't help but see parallels to Nexus of Fate in the current Standard, where it gives control decks a proactive endgame plan. The Bant Turbo Fog deck was once a big part of the metagame, and I could see such a strategy having a renaissance in best-of-one, especially because it's such a good answer to aggressive decks that might fill the ladder.

Another possibility is that control decks will thrive because they are natural homes for maindeck hosers like Negate, Duress, and sweepers. By their very nature control decks are reactive and full of disruption, so adjusting to include these hosers in their spell suites is no stretch. Such control decks would want to focus on card advantage and especially card selection spells that can dig for these hosers or move past them when they aren't useful in a matchup. A card like Opt becomes a sure staple, and would even bring into consideration Radical Idea, which can filter away poor cards. Jump-start is a perfect mechanic for control decks – which is why Chemister's Insight is already a staple – but a control deck with more extreme card choices might want the full playset. Surveil is also useful, and one in particular that seems fantastic for control decks in a best-of-one format is Thought Erasure. This sort of blanket discard effect works in any matchup – Thoughtseize would be an all-star. In the same sense, Counterspells are also very effective as catch-all solutions, so Sinister Sabotage looks fantastic.

Will Best-of-One Completely Change What Decks Are Viable?

One interesting thing to consider is that the best-of-one metagame could be so different from best-of-three that entire decks may or may not be viable in one or the other. For example, maybe in a best-of-one format a deck like Mono-Green Aggro, which is acutely susceptible to sideboard cards and has a weak one of its own, suddenly becomes competitive. On the other hand, maybe a deck like Golgari that relies on its sideboard will fall from grace in best-of-one. Perhaps Dimir Control, which has been completely outshadowed by Jeskai, will rise to prominence on the back of its many catch-all disruption spells. There's still a whole lot of questions about best-of-one to be answered, so it's going to be exciting to see how it develops.

- Adam