Tournament Magic is played best two games out of three, and tournament decks must have a minimum of 60 cards. In addition, a 15-card sideboard is allowed. After the first and second games, a player may swap any number of cards in his maindeck for an equal number of cards from his or her sideboard.
The existence of the sideboard adds a rich element of strategy to deckbuilding: What's the most effective way to use your 15 spots? Several different factors are worth considering, and many different approaches can be taken.
Now, in general, you want your maindeck to be the best 60-card configuration possible against the general field you expect. Sideboarding is to adjust your generally good deck for the specific matchup you are facing at any given time.
There are three different levels on which to approach sideboarding: against different categories of decks (aggro, control, combo, aggro-control, etc), against different exact deck types (Goblins, Burn, red-green aggro, red-black aggro), or against decks in general (the same switch-plan with little relevance to the actual matchup). Often you will address multiple levels in a single sideboard, as 15 cards afford a lot of options, and individual cards usually serve multiple purposes.
Against Specific Decks: Beyond that, especially once a format is defined, many specific decks are known. Not only will you be able to know how well your deck might fare against Control decks in general, you will be able to know how it does against, say, Dralnu du Louvre, a popular U/b (mostly blue with some black) deck, in particular. With enough testing, you will be able to know the best cards/strategies against this exact deck. For example, while Jester's Cap might only be marginal against control strategies in general, if you knew that a certain control deck only played three win conditions (cards to actually win with), Cap's stock would rise considerably if you knew you were likely to face that deck.
Against All/Most Decks: Remember that you're not just sideboarding against your opponent's deck as it existed in Game 1. They've also sideboarded and are playing a modified deck. Your target is the modified deck.
One approach here is switch strategies entirely in the sideboard (i.e., move out the fragile combo pieces and import a new strategy), or to make your combo more robust in general (board out combo pieces for 4 Coercions to help clear away disruption). This is often called a transformational sideboard.
A common technique based on this idea, although it may only in fact be applied against specific decks or specific archetypes, is for a deck to change gears completely. A control deck might board into a creature deck and catch an opponent without creature removal and with useless anti-control cards.
Building the Sideboard
What factors come into play when actually building a sideboard?
Necessity: Which cards are most worth having?
In general you will want to focus your sideboard on the matchups that need the most help. If you estimate your natural win percentage against a certain matchup is only 30%, then that's a lot of room for improvement. However, if you're already at 70%, gaining significant ground is going to be difficult.
Yes, you will also want to dedicate space to making sure your good matchups stay good. However, one thing to keep in mind is, again, that tournament matches are best two out of three. If your deck has a naturally very good matchup against another deck, you're likely to win the first game. If this is the case, you'll only have to win one of the last two games in order to win the match; you can afford to have a bit of a lower win percentage.
As a corollary to this, sometimes if a matchup is simply awful you might be better off giving up on it and dedicating your sideboard spots to other more tentative matchups. Many R/U (red-blue) “Owling Mine” decks, like the one I mentioned last week, didn't even bother having a strategy against their worst matchup, aggressive red decks, because the potential gain wasn't worth the effort. This is rare.
Another note on necessity: Use your sideboard to answer strategies that would otherwise dominate you. For example, if your deck can't possibly beat a Worship or a Glare of Subdual, you will probably want answers to these cards in your sideboard.
Power: Which cards are most powerful?
In the maindeck, a card like Perish would be silly. Against the majority of the field it might as well be a blank. But against a minority of the field, the card is devastating.
The sideboard facilitates the practical use of these sorts of cards. You want your sideboard to be chock full of cards that are very powerful. However, these days, thanks to smarter design and more diverse fields, such obvious examples, hyper-powerful “hosers,” are both harder to come by and less effective.
It is sometimes possible to devise a sideboard plan – sometimes a certain card, sometimes a combination of cards – that perfectly exploits another deck's exact weakness. These types of sideboard plans are highly worthwhile, even if they take up a few extra spots, since they can totally change a matchup, and often can do so regardless of whatever an opponent is bringing in, if their overall strategy is still inferior.
In this year's World Championship finals, Makihito Mihara beat Ryo Ogura 3-0 in a matchup I'm confident that, coming into the tournament, Ogura thought he was a favorite in. However, in the second and third games, the result seemed like a forgone conclusion as Ogura's control deck, despite boarding in several cards, had no suitable defense against Mihara's combo deck plan of storage lands (Calciform Pools) and Gigadrowse, building up a huge amount of mana and tapping all of Ogura's lands.
As another example, at Pro Tour – Charleston this year I played a GWu (green and white with some blue) Glare of Subdual deck. One matchup I was especially concerned with was the mirror. Common knowledge suggested that it was all about the card Glare of Subdual – either finding one's own, or destroying the opponent's. Instead, I realized that most Glare decks couldn't destroy a creature. With this in mind, and 4 Chord of Callings already in my sideboard, the simple addition of a single Blazing Archon gave me a leg up no matter how many enchantment removal cards my opponent brought in.
A good sideboard is filled with dominating strategies.
That said, powerful individual cards still also have their function.
Especially with today's diverse fields, in order for a sideboard to cover all bases with only 15 spots, it's important for sideboard strategies to have as much overlap as possible. You'll want to either devise strategies that can apply in multiple matchups (Calciform Pools/Gigadrowse, against almost any control deck), strategies that employ many of the same cards (Chord of Calling/Dovescape, Chord of Calling/Blazing Archon), or cards that are good on their own against entire categories of decks (Duress).
Occasionally players will play an extra land in the sideboard, or a card that is similarly versatile. While this card would not be especially powerful, its application is widespread.
A special consideration is made for decks with tutors. The term tutor refers to a card that can search for another card. This sometimes motivates hyper-versatile sideboards, because multiple copies of a tutor already account for a necessary quantity of even a single card from the sideboard.
I made the Top 8 at Canadian Nationals in 1999 with a deck playing 4 Vampiric Tutors. This was my sideboard:
1 Arcane Laboratory
1 Gilded Drake
1 Dread of Night
1 Stromgald Cabal
1 Rapid Decay
1 Tranquil Grove
1 Spike Feeder
1 Sacred Ground
1 Root Maze
With the tutors, any time I boarded in a one-of, it was functionally as if I actually had five copies. A modern example of a tutor would be the aforementioned Chord of Calling.
Space: Which cards do I have room for?
The aspect of space in sideboarding is often overlooked, even by tournament players.
Space is governed by two factors: a deck's natural density, and the matchup at hand.
Some decks are denser than others – that is, the number of cards necessary to a deck's fundamental strategy varies. One deck might need a certain 55 cards to operate properly (say, a combo deck), and another, looser, aggro deck might only need about 45. A dense deck is better off boarding in small clusters of powerful cards, whereas a looser deck can afford to board in larger clusters of versatile cards that can come in handy in several matchups. Sometimes you'll hear players complain that sideboarding with a certain deck is very difficult: “I never know what to take out!” This is usually the case when a deck is dense.
Players will add cards to their sideboards (say, 4 Perish), without considering what they will take out to bring them in the appropriate matchups… but this is a big factor. It is possible to board in so many one-shot powerful cards that you begin to injure your deck's main strategy.
Sometimes it's worth exceeding these limits if what you're making room for is powerful enough, but these natural cues make good guidelines for how many cards you'll want to dedicate to a given matchup.
An easy way to become more prepared for a given tournament is to work out sideboarding plans in advance. What comes in and out in every matchup that you can anticipate (even ones that might only occupy a fraction of the metagame)? Considering this question is easier in the comfort of your own home than in two minutes in between games at a tournament. It will also help you identify cards that are not pulling their weight. Believe it or not, many tournament players do not do this, because it is somewhat tedious work. I myself have realized, midway through a tournament, that a certain card in my sideboard is useless because I don't have room to board it in (any replacement I would make for it would only make the deck worse) in the matchup I had planned to use it in.
In a tournament a sideboard plan might suddenly seem not to be working, or you might find yourself against a deck you hadn't expected or a version you hadn't anticipated. You will always have to make decisions on the fly, but understanding your deck, and making as many decisions as you can beforehand, only helps your chances.
See you next week!