Having a well-functioning sideboard is an important part of succeeding at competitive Magic, so naturally we want to learn how to build our sideboards in the best manner possible. This can prove to be a bit tricky, as properly constructing a sideboard from the ground up is quite a complicated endeavor. This article is an attempt to break things down and share my personal theory on sideboard building.

What follows is a list of things you can do to better approach the task of constructing a sideboard in Legacy.

Understand the matchup.

One common mistake when trying to improve a matchup is adding cards that are “good” against the deck you’re trying to beat without considering the intricacies of that particular matchup. For example, Krosan Grip might be an excellent card against Miracles out of RUG Delver. BUG Delver on the other hand already has Abrupt Decay to deal with Counterbalance, and thus may be better served by a card like Painful Truths.

It helps to think of each of your cards as serving a specific purpose in a matchup. Against Storm, cards like Duress and Spell Pierce are a great way to slow them down and buy you some time, but unless you make good use of that time you will still fall short of victory. This can be done in a number of different ways. Delver decks put on a fast clock and kill the opponent before they have time to assemble the combo. Miracles can deploy a Counterbalance lock and take control of the game that way. The important thing is having a plan.

About two years ago I found myself unhappy with my Miracles matchup. Being a long time Goblins player I was still a favorite to win, as Miracles could rarely keep up with the steady stream of card advantage provided by Goblin Matron and Goblin Ringleader. But if they were able to prolong the game long enough to resolve a big Entreat the Angels I would still lose, and it wouldn’t matter that I was up four or five cards.

Once I had identified the problem I was much better equipped to solve it. Rather than splashing for something like Krosan Grip, I added a copy of Earwig Squad to my deck to preemptively deal with Entreat the Angels. My results improved dramatically.

Look for what matters in a specific matchup, whether it’s a key card or a concept like card advantage or mana development. Narrowing this down to a few key points makes it easier to focus on the bigger picture, and also helps you waste fewer resources fighting the “unimportant” battles.

Sometimes however you will find a matchup that seems borderline unwinnable. It can be a linear strategy that is too powerful for you to keep up with, like B/R Reanimator, or a deck that is capable of overloading you on so many fronts that it might seem impossible to fight, like Shardless BUG.

You can either ignore such a matchup and hope to dodge it, or you can aim to radically alter the nature of the matchup in a way that favors you. If you can’t answer your opponent’s threats, take the proactive approach and force them to have the answer instead. A powerful, narrow card like Blood Moon might be just what you need to beat that pesky Shardless BUG player.

Maximize your sideboard slots.

Your sideboard slots are among your most precious resources. Make sure you get the most out of each one. This is especially true for reactive decks that try to answer everything that their opponents do, but holds true for the more linear and proactive decks as well. You only get fifteen actual sideboard slots, but there are still ways for you to effectively increase the number of slots you have.

The first is to play sideboard cards in the maindeck. This could be a metagame call, such as when people play maindeck Pyroblast due to blue being so heavily represented in the metagame, or it could mean playing cards that are not great in most matchups but not really bad in any of them either. Some examples: Cabal Therapy and Abrupt Decay in Delver decks, or even Bayou out of Ad Nauseam-Tendrils. Cabal Therapy might be aimed at combo, and Abrupt Decay at Counterbalance; but they still have utility in other matchups, even if they aren’t the best things you could be doing. The upside of this strategy is that you will generally be more favored in post-board games, since you now have more powerful cards in your sideboard. The downside is that your maindeck will be less streamlined. It’s difficult to say which is going to be the correct choice. Just remember that you have the option. Be mindful of when it might be right to sacrifice some consistency in exchange for more room in the sideboard.

The second way to effectively increase your number of sideboard slots is to play more flexible cards. Dimir Charm may only be one card, but you can count it as both an anti-combo slot and an anti-creature slot; thus effectively getting two slots for the price of one. This is not without cost however, as Dimir Charm is less efficient than either Flusterstorm or Fatal Push. If you go down this route, the most important thing to keep in mind is whether or not the card is still efficient enough to do what you need it to do. You don’t want to be forced to decide between killing their Stoneforge Mystic or deploying your own on turn two because you couldn’t play your removal spell on turn one.

Finally, you can utilize the power of utility lands to gain more slots against a particular deck or strategy. Wasteland, Karakas, and Tower of the Magistrate are all powerful options when you want additional tools to help you fight a certain matchup. This works best in decks with higher curves, since they tend to have less heavy color requirements. In my Goblins deck for example, having red mana is important. But once you have that, the number of lands you have starts to matter more than how many red sources you have access to. Because of this I can afford to play cards like Wasteland and Karakas—it is rare that I would draw enough lands, while not drawing enough red sources.


The Legacy metagame is very diverse, encompassing hundreds of different decks.  With so many different decks in the format, it’s practically impossible to prepare for all of them. What we can do however, is prepare for when we need to adapt. One way to do this is to diversify our sideboard cards. Often you will have a pretty good idea of how many and what kind of cards you want versus different strategies. Maybe you take out your countermagic for more creature removal when playing against creature decks, whereas you side out all of your removal spells for hand disruption when facing a combo deck.

This is a good rule of thumb to have, as it helps when thinking about postboard configurations even in matchups you’re unfamiliar with, by placing them into categories. Lands is weak to graveyard hate and Blood Moon, but not to sweepers. Dredge is weak to graveyard hate and sweepers, but not to Blood Moon, and so on. Where it gets interesting is when you begin to more closely examine the various decks and their weaknesses. Let’s say you’re deciding on which graveyard hate to play. You want to dedicate about three or four sideboard slots to it, and you’ve made a list of graveyard decks you expect to face:

  • Lands
  • Reanimator
  • Tarmogoyf decks
  • Dredge
  • Storm

How do you decide which cards to play? Grafdigger’s Cage might be the best choice against Dredge and Reanimator, but it’s useless against Lands and Tarmogoyf. Surgical Extraction is weaker against Dredge, but is very good against Lands. Relic of Progenitus might be the best option, since it is useful against all five decks. However, if you only need two more cards versus the Tarmogoyf decks, there’s no point in playing more than two Relics. At this point, the other options begin to look more appealing again, and so you might settle for the following configuration:

2 Relic of Progenitus
1 Surgical Extraction
1 Grafdigger’s Cage

By doing it this way, you ensure that you will have a sufficient number of cards against each deck, while maintaining an as high as possible power level. Diversifying your cards like this also makes it more difficult for your opponent to combat your stategy: they can never be sure of which pieces you are going to draw. When choosing your sideboard cardswhether it’s what artifact destruction to include or which graveyard hate to playyou want to consider which strategies you are trying to prepare for, and how many cards you need versus each deck.

If your sideboard discard spells are all copies of Thoughtseize, you’re going to have a difficult time sideboarding against Burn decks. With all Pyroblasts and Flusterstorms you risk finding yourself cold to Sneak Attack. The more diverse our sideboard, the more potential postboard configurations we have, and the more likely is it that one of them will be good against a particular deck.

The other reason we might want to diversify can be understood by looking at the power level of our cards as relative rather than static. Fireblast is an excellent card, but you rarely want to draw the second copy, as it will often be straight up uncastable.

In a similar vein, the more copies of Dark Confidant, Dismember, and Painful Truths you play, the more real becomes the cost of losing life. Pyrokinesis is a great card, but the second one is often worse than the first because you no longer have extra cards to pitch to it.

(The opposite of this is cards that get better the more of them you play. Think of how the first Lava Spike does very little, whereas the seventh one can mean the difference between life and death.)


Identify key cards in a matchup to help you focus your resources on that which is most important. If a matchup is deemed very unfavorable, consider if a powerful but narrow hate card might be the best way to improve that matchup.

You can effectively increase the number of sideboard slots you have by moving some cards into the maindeck, playing more flexible cards in the sideboard, or utilizing the power of utility lands.

By diversifying your sideboard cards you’ll have more options during sideboarding, and will make it harder for your opponents to adjust.

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