When I was writing my article about deckbuilding (Why deckbuilding is good for you) I wrote a few thousand words about sideboarding alone. Even though I deleted all that I decided to give it a second chance and publish a standalone article about sideboarding. Similarly to deckbuilding, building a sideboard and sideboarding is also something many players neglect - or rather they do not give the sideboard enough credit. 15 cards may not seem like much but it is something that will give you an edge against others in a tournament. Again, if you want to be successful Magic player, a good sideboard and boarding well is something that will make your win rate go higher. Just the fact that we play more games with sideboard cards should make us realize that. The difference is big, not just a slight one.
This article is about sideboarding in constructed, but it is as important in limited. I think that playing limited alone should give you a deep understanding of how to sideboard - limited is about building a deck and finding cards that can help against strategies our decks are weak to. Since we work with a smaller amount of cards, we can see the intricacies easier. Unfortunately not so many people even sideboard in games of limited! If you are one of such players, start picking sideboard cards or start sideboarding in your next sealed deck event.
I'm no pro player and no sideboarding expert but what I can tell you is that when I was consistently successful in competitive tournaments it was always during times when I knew what my sideboard should look like and why. I could create a different deck out of my sealed pool that was better suited against the deck I played against and not fearing this, I was able to win more matches. I was capable to build a constructed sideboard on the spot without much thinking. When I have no idea what to even put in my sideboard it usually results in lower win rate. I was never a fan of reading sideboarding guides nor trying to memorize those (they did not exist at that time anyway). Many of those guides differ and even if you look at videos online, many people board in different manner even if their sideboards are relatively the same. When I wrote an article about Death and Taxes some players were telling me to never take out Mother of Runes out of my deck. While I made a mistake when boarding all Mothers out it was because of one card I forgot about. For my game plan against Miracles I was correct to take out the Mothers out. I just did not realize that I put Sanctum Prelate in my deck which did change the number of Mother of Runes I'd like to take out. Anyway even just this one mention was something people started arguing about. Who was right? Sideboarding is very complex. It requires a deep understanding of your deck and current metagame and can also depend on your approach and plan. Often you and the person you might be arguing with about sideboard card choices may be both right. Sideboarding is very dependent on context and reading your opponent (this is something you can do online as well, you need to see what kind of player your opponent is - passive, aggressive etc., unless you are playing a linear combo deck you should be able to discover this to some extent from seeing how your opponent handles certain interactions). Context can be anything from the latest winning decks, your opponent, the role you choose to play against certain matchup etc.
The best thing as usual is to go through the whole process of deckbuilding and analyzing the metagame. Then figuring out how to sideboard becomes way easier because you already know what cards are dead in certain matchups and what strategy works best against certain deck. Knowing this is crucial and knowing how many cards you need to replace is invaluable because then you won't get tendencies to overboard, which also means that there won't be 'dead slots' in your sideboard.
I will digress a bit first. When I start to build something on Magic Online my sideboard at first contains cards that I consider playing main deck. It is not because I'd want to play those cards in my sideboard but because I still need to figure out how my 60 cards should look like. Playing like this allows me to see what cards are good against what decks and which cards are worth playing main deck and which should not be there. When Ancestral Vision was unbanned I was trying different kind of builds of Faeries and my deckbuilding process was exactly like that. I started from scratch and did not use much prior experience with Faeries in Extended or Standard into the process because I was going to play in an unknown format for me. Sometimes post-board I had access to red or black if I was on mono-blue (but I was trying to make UB Faeries work). That is why for example my main deck featured certain amount of Remands (usually 3-4) but I had no replacement for it post-board. In the past I usually had Negates or Flashfreezes available but not this time around. In the games I played a large amount of my opponents called me names and some just conceded when they saw me play Remand post-board. There was a Burn player that after terribly dying to my Kalitas and singleton Dispel that saved my life asked me why I had those terrible Remands still in my deck. I explained him why, he thought about that for a bit and then wrote me that it actually makes sense. He did not expect me to be in the process of building a deck and playing with a deck that is still not complete.
The reason I was called names or wasn't allowed to finish my match was most probably because my opponents expected me to be a bad player not worth playing against if I can't sideboard properly. They did not consider the fact that I played without sideboard. Not being able to sideboard is something that will affect your win rate a lot (if you forget your sideboard, ask for the cards, or buy even some cheap cards that can replace the cards you usually play). So even if your deck is not yet fine-tuned prepare a proper sideboard at least against those decks that you are bound to ran into in big numbers. If you expect graveyard strategies put graveyard hate in your sideboard. If you play a deck that needs to win with an artifact and is dependent on it be ready to face artifact hate. If you are aware that Empty the Warrens won't kill half of the field, put a secondary win condition in your sideboard (Tendrils of Agony). Depending on your deck's role you should know that you will need cards against fast aggressive decks and control decks. This can mean playing some sweepers in the board against aggressive decks or discard and some hard counters against control. The sideboard will most likely contain a wrong number of cards against different decks and even the choice of the sideboard card may be wrong, but it will give you the means to get rid of dead cards from your main deck and have access to cards that are actually useful.
This is a post-board game with UW Control with transformational sideboard that contained creatures like Soldier of the Pantheon, Fiendslayer Paladin and Archangel of Thune against decks that were boarding out global and spot removal.
There are three different types of sideboard you can run. Either traditional which usually consists of a mix of silver-bullets and answers, transformational sideboard that consists of bringing in a different game plan, or targeted sideboard that primarily focuses on one dominant deck. Most of the time you will be running a traditional sideboard. If you'll be playing a linear combo deck you are most likely to run a transformational sideboard. But these are not just a combo deck thing. A control deck can also run such a sideboard, boarding in aggressive creatures against decks that side out removal. The last sideboard type is rare, but sometimes the metagame is rather binary. If one of the matchups is good you and concentrate on the other one which is not and dedicate your sideboard to it.
General rules about what to put in your sideboard follows. First cards to go in your sideboard are the ones you can't play without. In Vintage if you are not ready to beat Dredge or Shops you won't probably do good even if you can beat any blue deck there is. At a certain point in Extended there used to be field full of Affinity decks and Dredge decks. You just couldn't show up at a tournament not running artifact hate and graveyard hate. Second what you need are cards that will help you win matches up that are close. If your win percentage is around 45-55 you want to make it more like 60 at least post-board. Next what you should look for are cards for your good matchups. Your opponents will be siding more and might even change their strategies and you should be ready for it. Sometimes it only comes down to switching an ok card for a better suited one, it can even have the same effect but being cheaper (the cards are usually too narrow to play main deck - for example Mana Leak vs Flashfreeze). At this point you should also add cards that will help you win a mirror match. If you want to be successful, a well thought out plan against mirror is a must. The last thing you should address are your bad matchups but those that you can win. Those that are not winnable are not worth preparing for. You just have to hope to dodge them.
2. Keep integrity of your deck
The second rule that should be understood and is probably the most obvious one is to keep integrity of your deck. This may be obvious to many, but for some players it isn't. Many players that net deck can run into problems of how to sideboard properly or how to even prepare a sideboard. Note that even if you net deck, you should still create your own sideboard because it is dependent on metagame and also your ability to play a certain strategy and executing certain plan.
Diluting your deck is one of the problems that can cause your deck to crumble. Imagine that you are playing The Epic Storm or any other combo deck that requires several pieces to come together to win. You wouldn't side out something that you need in order to combo off, right? This is most noticeable if you play aggressive decks like Red Deck Wins. Those kind of decks are good at what they do - kill the opponent fast. Adding sideboard cards into Red Deck Wins always makes it slower because you take out cards that are usually played proactively to beat your opponent. The deck will become less efficient at what it was meant to do but it is worth it if you need to stop a combo that can be faster than you for example. You should only board in cards that are necessary against what you play. If you play a midrange deck taking key cards of your deck or diluting your deck too much won't be as noticeable. You may not even realize that you are doing it.
One of things that can happen apart from overboarding is that you may not board certain cards out that may either become useless or will be risky to play. Either way you do not want that because post-board you want to maximize your chances of winning, not a gamble. For example if you are on TES and playing against a deck running Deathrite Shaman that might even board in some graveyard hate you don't want to keep Past in Flames in your deck. You should also consider changing your win condition because such a deck usually plays Golgari Charm or another kind of sweeper that can deal with your 1/1 Goblins. Winning with Tendrils of Agony is safer. Ad Nauseam is not a card to rely on if you are facing UR Delver or Canadian Threshold. If you are playing relatively creature heavy deck that boards in global removal, you should reconsider the number of creatures. Take out the worst creatures and put in alternate win condition. Usually a planeswalker or some late game high impact creature.
3. Have a plan, use your opponent's sideboard strategy against them
Often sideboard cards are answers to something. But sometimes the cards in the sideboard may allow you to use a different strategy that your deck is not good at normally. If you are on Dredge in Vintage you know that everyone will board in graveyard hate against you. All decks need it in a quite high number. You can either put answers to that in your sideboard - Nature's Claim, Wispmare, Serenity etc. - or you board in a different win condition - Dark Depths, Thespian's Stage. Your opponents' decks will be diluted, less consistent and usually not prepared for Marit Lage. They might be, for one. But since Dredge can play Petrified Field it's not that difficult to put the two lands together again (and Bazaar of Baghdad looks for them fast). If you are playing Valakut, the Molten Pinnacle based deck for example, your opponents will also be taking our removal of their decks to put in cards that can possibly stop you from killing them with Scapeshift. In that case you can just put in Tireless Trackers. Since you ramp and your opponent won't be playing Lightning Bolts post-board you can just profit. You should be aware though that sideboarding is also something that requires you to assess your opponents. Depending on how they play and their skill level, you might want to sideboard differently. Some players may not be good at sideboarding so against those boarding in a different plan might simply fail. Some players are more proactive and try to make their strategy simply go through, some players look for answers to what you might bring in and be more in control. I board differently against these players and you should also if you can distinguish players' tendencies. If you don't know what I mean with this, just try to see how games look against your play buddies or opponents you face often. Compare those games against players you've never met. See the difference?
4. Sideboarding may differ depending on who is on the play
Relatively often you may find yourself in position that you want to sideboard differently on the draw and on the play. To know when to do that comes from knowing your deck and strategy well. I'll give you The Epic Storm example. If you are on the play against Death and Taxes, what you need to do is win as fast as possible. On turn one you can try to help your draw a bit with Ponder. On the draw though your primary concern (unless you can win on t1) on turn 2 is discarding Thalia, Guardian of Thraben or Ethersworn Canonist. If any of those hatebears ends up in play you simply do not want Ponder but rather Abrupt Decay to deal with those. If you'd be playing a 4c Legacy Delver against Shardless BUG for example you will be boarding out a different amount of Forces depending if you are on the play (-4 Force of Will) or on the draw (-2 Force of Will, depending on how many cards your deck cannot handle with sideboard cards, for example if you can't deal with Sylvan Library or True-Name Nemesis, you'll be forced to keep more Forces in as they are still the universal answer to anything).
Sometimes you may find yourself in a situation when you can board out a land. A Delver deck is a good example. If you do not need Wasteland against your opponent's deck and your opponent won't disrupt your mana base (Miracles) you can take 1 Wasteland out. If there is no need for this, you can just leave your mana base as is. In most constructed formats having lands in the sideboard is not worth it unless they are your alternate win condition. But from time to time a metagame that calls for it comes. In limited however boarding a land in (on play) or boarding one out (on draw) is something that will help you keep the right percentage of hitting x lands on turn y. This will of course depend on your deck but usually you want to hit your 4th land drop on turn 4 with 71-75% chance which will simply give you the information that you need to change your land count depending on who starts. Since you can have unlimited basic lands in limited deck sideboard, there is no reason why not do this if you want to have the best chance not to flood out or get mana screwed (to see in more detail what I mean you can check my article about mana base - Show and Tell: Mana Base)
Finals of some GPT. I wasn't even counting on the possibility I'd encounter something like Bogles. My opponent was ready for Melira Pod though as that was the most played deck at the time. The Suppression Field, Stony Silence, Leyline of Sanctity and Grafdigger's Cage I had to face during the deciding game simply decided the game. There was no way I could combo off unless I would have drawn the exact 4 cards I had to deal with those 4 cards.
The sideboard is very important. Most of the time in competitive environment you will be facing more or less the same decks. Pre-board, those decks will often be very similar. But sideboards may be totally different. It is something that will show who is better prepared for the current metagame no matter if you are playing constructed or limited. The most important when creating a sideboard and using it is to have a plan. Even if you won't sideboard properly, if your plan is good and the cards help your plan, it will give you more edge than not boarding at all or incorrectly. Everything is something you can learn and comes with experience, so do not be afraid to experiment and explore. Just make sure to know why you have the cards in your sideboard and what are their 'weaknesses' (you always trade something for something).
-S'Tsung (stsung on Magic Online, you can follow me on twitter -> @stsungjp)