It's easy to explain, even to someone unfamiliar with the game, that a Magic deck consists of 60 cards, with a limit of no more than four copies of any particular card (except for basic lands, of course). It's a bit more challenging to teach them about the extra fifteen cards that come along with—yet are not part of—the deck. Harder still is the task of conveying just how important those cards are, and how vital it is to choose them carefully.
Tournament matches are typically determined by a best-two-out-of-three set of games. For the first game, both players play with their main decks—their primary 60 cards that will be the same for the start of every match. After Game 1, the players have the option to swap in any number of the fifteen cards from their sideboard in an effort to tailor their deck toward winning the next game.
Technically speaking, it's legal to play with a deck of more than 60 cards, but at all times your deck must be at least 60 cards and your sideboard must be at most fifteen cards. (Except in Limited. For a discussion of sideboarding in Limited, see this article.)
Sideboards win tournaments. Because your sideboard cards can be more specialized—pinpoint focused for a certain task or matchup—they're often your most powerful tools. Sometimes, sideboarding can be the most important factor in determining how two decks will match up against one another. Building and using your sideboard well will be crucial to your tournament success.
Let's go over a few of the useful things your sideboard can do for you.
You sideboard with the goal of making your deck better suited for a matchup. What simpler way is there to accomplish that goal than to bring in the perfect answers for your opponent's threats?
A classic example of a sideboard card is one that destroys artifacts and/or enchantments. Except in extreme circumstances, players choose not to main deck cards like Smash to Smithereens out of fear those cards will be dead—useless—against certain opponents. However, it's nice to have access to Smash to Smithereens in your sideboard for when you face a deck that's particularly reliant on artifacts—like the one featured toward the end of this article.
Similarly, if your opponent has lots of enchantments, you might want to sideboard in more answers to enchantments. If your opponent is trying to win via a swarm of cheap creatures, you might want a board sweeper like Languish. If he or she has a particularly devastating spell, perhaps Negate is your best bet.
Your sideboard lets you find the perfect tool for any job. Playing Game 1 ought to show you exactly what "the job" is in the case at hand.
On the flip side, you can also use your sideboard to find a new threat that your opponent will (hopefully) struggle with. You might go about this in a number of different ways.
First, you might simply add more threats in an attempt to overload your opponent's answers. Imagine, for example, that you face a control deck that features very few creatures. During sideboarding, you get to take out some of your ineffective creature removal and increase your concentration of threats, which ought to be tremendously helpful.
Alternatively, you might just make some upgrades to your existing threats. Against a deck with board sweepers, a creature like Hangarback Walker can give you a bit more resilience. A Goblins deck might be interested in Subterranean Scout against a deck full of annoying blockers. Sideboarding is about perfecting your deck for the matchup, and a few minor upgrades can be a big part of that.
Most often, though, you'll sideboard with the goal of diversifying your threats. It's all about sticking a threat that your opponent cannot effectively answer. And the more angles you can attack from, the better chance you have of doing so. One exciting new sideboard card for red decks is Molten Vortex. Control decks will try to shut you down by killing off your creatures and countering your burn spells. That said, there's not a lot they can do to overcome the slow bleed from a Molten Vortex in a protracted game.
In general, look for planeswalkers and other noncreature threats as excellent sideboard cards against slow decks.
Answering problems and adding threats are examples of versatile ways to use your sideboard slots. Over the course of a long tournament, you're likely to turn to these cards often, as they'll serve as minor upgrades in a lot of matchups. However, another approach is to look for hate cards—single cards that are extremely effective at beating (hating out) a particular deck, color, or strategy.
With Orbs of Warding, for example, decks heavy with burn spells will hardly be able to touch you. Gaea's Revenge is a nightmare for blue control decks hoping to sit back on permission spells and removal. Tragic Arrogance can utterly demolish a creature ramp deck like Green Devotion.
A rule of thumb is that the more extreme a strategy is, the easier it will be to sideboard against. You can hamstring a small creature deck with a cheap board sweeper like Languish. You can shut down a combination deck by knocking out one of their pieces before they can properly set things up.
Any time you find yourself with extra space in your sideboard, identifying and playing with hate cards against a popular deck is a great way to improve your chances in a tournament. You might not use them quite as often as your versatile sideboard cards, but sometimes they can swing a matchup in your favor at the low cost of only a sideboard slot or two.
The most interesting thing about sideboarding is that it's done in secret. Most of the time, your opponent won't even know what cards are in your sideboard, let alone which ones you'll choose to bring in for Game 2! This means that every once in a while you'll have the chance to take an opponent by surprise, employing a strategy he or she hadn't expected or prepared for.
A simple example would be a control deck with very few creatures in the main deck. If your opponent sideboards out a lot of his or her creature removal while you sideboard in a number of threatening creatures like Jace, Vryn's Prodigy or Hangarback Walker, you might be able to steal an easy win.
On the other hand, a seemingly aggressive Jeskai deck might transform into a more controlling deck by sideboarding in End Hostilities, Elspeth, Sun's Champion, and Dig Through Time. An opponent who goes overboard with creature removal and life gain can be easily outdone in the late game.
Transform sideboards can be fun and impressive when they work out, but I recommend turning to them only as a hail mary when nothing else is working. After all, sideboarding should be about perfecting your deck, not about clumsily trying to employ two conflicting strategies at the same time.
HOW TO BUILD YOUR SIDEBOARD
Building your sideboard is a task that's as challenging and as important as building your main deck. From my experience, though, it's typically given only a small fraction of the attention it deserves.
The Elephant Method
It can be quite difficult to hone in on the perfect fifteen cards. One way to start the process is to employ the elephant method. Legendary deck builder and Pro Tour Hall of Famer Zvi Mowshowitz explains the elephant method as:
"Writing out ideal realistic lists for all matchups and then trying to make the unique cards in those lists add up to 75 cards before deciding on the specific 60 for the main deck and the specific fifteen for the sideboard."
When you employ the elephant method, you're thinking of your deck as a complete 75-card unit. First, you consider what you'd like your deck to look like after sideboarding in each of the matchups you expect to face. Next, you make sure you have the proper number of cards to bring in and take out in each matchup. Finally, you construct your deck and sideboard accordingly. In short, you look at the big picture, and your sideboard is as important to the big picture as your main deck is.
One common pitfall to avoid is over-sideboarding. It's dangerous to bring in so many sideboard cards that you compromise the original game plan of your deck. In sideboarding, continue to pay close attention to your creature count, your mana curve, and the other important details of your deck's composition.
For example, if you're playing an aggro deck, you might encounter a problem if you swap out six creatures for six answer cards. You're liable to lose too much of the aggressive potential that made you choose the deck in the first place!
Similarly, if you're playing a control deck against a fast aggro deck, you might be unimpressed by a card-drawing spell like Read the Bones, especially since it causes you to lose life. To be sure, Read the Bones is not one of your "best cards" in the matchup, but you do need to maintain a certain density of powerful late-game cards, or else you might no longer be able to win! Many times, I've made the mistake of sideboarding in too many cheap removal spells, only to find myself suffering from mana flood and losing the long games that my deck had been originally designed to win. It's possible that Read the Bones is so important to the overall structure of your deck that you should leave it in, even against an opponent who's attacking your life total.
The first thing to recognize is that Mr. Sigrist's deck had a very specific and focused game plan, so the risk of over-sideboarding was especially large. If he was to take out too many cheap artifacts, his Ensoul Artifacts would lose their effectiveness. If he shifted gears and became too defensive, he wouldn't be able to get his opponents into range of his Shrapnel Blasts.
So Mike's sideboard consisted mostly of cards that answered his problems. Roast is excellent against green creature decks featuring Courser of Kruphix, Siege Rhino, or Whisperwood Elemental. Seismic Rupture offers defense against creature swarms, and might even be considered a hate card against mono-red. Disdainful Stroke is effective against any slower decks that rely on expensive spells.
Important to note is that when Mike would bring in these cards, they would either be upgrades for the reactive cards in his main deck (Stubborn Denial or Collateral Damage), or he would only make small adjustments here or there. A top priority was always to maintain the structure and mana curve of his deck, and make sure that he could still function at maximum efficiency after sideboarding.
His final three slots were Thopter Spy Networks, which served as a way to diversify and upgrade his threats in matchups where he needed a little extra late game power. Decks like Abzan Control and Blue-Black Control would seek to defend, slow down the game, and grind small advantages. Thopter Spy Network would make this plan look silly by ensuring that Sigrist's opponents would be buried under a mountain of card advantage.
Practice with Sideboards
Sometimes the way two decks match up after sideboarding has virtually no resemblance to the way they match up in Game 1. When this is the case, you want to know about it ahead of time instead of facing a trial by fire in the actual tournament.
Like most things in Magic, there's no secret recipe to building a perfect sideboard. The key is simply to give it the attention it deserves rather than throwing it together the morning of the tournament. Personally, in the late stages of my tournament preparation, I like to be playing virtually all of my practice games with sideboards. In preparing for a tournament, if you aren't playing any sideboarded games, or are doing so only as an afterthought, I recommend rethinking your process to give your sideboard some extra emphasis. A little bit of work on your sideboard will pay off in a big way.