How to Build your Sideboard in Legacy

Sideboarded games are very important, and you play them roughly 50% more than you play preboard games, so they are disproportionately important in increasing your win percentage. Feel free to skip the following section if you are uninterested in the math.

Match-Win Percentage Formula

Let X be your presideboard win percentage. Let Y be your post-sideboard win percentage. Let Z be your match-win percentage. Then:
Z = Probability (win G1 and G2) + Probability (win G1, lose G2, win G3) + Probability (lose G1, win G2 and G3)

probabilityone

Which simplifies to:

probabilitytwo

There isn’t an easy conclusion to draw from this formula, but I personally keep track of all of my wins and losses and use this formula to determine my match win percentage for every deck I play. How does it relate back to sideboarding?

Well, the use of the formula shows that post sideboard games are extremely important. If you win 50% of your game ones, then your match win percentage is the exact same as your post sideboard win percentage (Y). But, if you win 50% of your post sideboard games, then your match win percentage is just 0.5X+0.25.

Plugging in some numbers, this implies that if you win 60% of your game ones, your match win percentage is 55% and if you win 90% of your game ones, then your match win percentage is still just 70%. To contrast, a 90% post sideboard win percentage would mean that you win 90% of your matches!

Of course post sideboard games are important, but I just wanted to highlight mathematically just how important they are. When comparing decks, make sure to use the above formula instead of a “raw win percentage.”

In Legacy, this translates directly to the fact that for the most part, fair decks tend to perform better in long tournaments than unfair decks. The sideboard cards against degenerate strategies are a lot more powerful than the sideboard cards against fair strategies.

Sideboard Construction

Now, onto some actual sideboard construction guidelines. The most important thing is to make sure you have a complete sideboard plan against all of the decks you are trying to beat, and understand what trade-offs you are making. Typically, when I first start exploring an archetype, I take a look at successful lists with the archetype and pick and choose the flexible main-deck slots based on what I expect to be popular. Typically, I hedge toward beating fair decks game 1, as combo decks can generally be managed post-sideboard. Then, once I have my main deck, I go through all of the top tier archetypes and determine how many cards I would like to cut from my main deck. Then I slowly construct a sideboard by adding cards and checking off the decks I am attempting to beat in order of priority.

For example, my first order of priority these days is beating Miracles. Let’s say I wish to cut 5 cards against Miracles when I am playing Grixis Delver. Then, I pick a specific coherent 5-card sideboard plan against them and add those 5 cards so that I have 5 of 15 sideboard slots. A card like Flusterstorm has applications for beating Miracles and beating combo decks, so I check off a couple slots for the combo decks I plan to bring them in against. Then I look at the next deck on my list and continue this process. By building from the bottom up, I ensure that I know exactly where my 15 valuable slots are going and what matchup trade-offs I’ll make, as well as which cards make up the last few slots of my sideboard. Knowing the “last few” tells you which cards should be the first to go if you are trying to tweak your sideboards to beat specific strategies.

Coherent Sideboard Plans

Another critical aspect of your sideboard plan is coherency. These days, I see Delver decks running Painful Truths, partly as an attempt to outgrind Miracles. Now, if Painful Truths is a key part of your game plan, then I think you should A) have an answer to Counterbalance and B) cut all your Dazes. If you have all the cards in the world but are under a Counterbalance lock, it won’t do you much good. Similarly, if you are trying to outgrind Miracles, drawing cards like Daze when the game goes long is awful.

Along with coherency is effectiveness. I personally don’t find the Painful Truths grind them out plan effective in Grixis. The cards simply aren’t there to outdraw Predict Miracles in most situations. But the new 4 color Snapcaster Delver lists have a lot more built in card advantage and this is a potential path to beating Miracles. In my opinion, Grixis Delver should leave in some number of Dazes against Miracles and focus partly on the tempo plan, whereas 4 color Snapcaster Delver should side out all of the Dazes and try to play a midrange game.

I will split the next section of the guide into 3 categories: fair blue cantrip decks, fair non cantrip decks, and unfair decks. Using Wishes doesn’t really change any of these macro-categorizations, it merely limits your sideboard slots.

Fair Blue Cantrip Decks

Let’s take a look at a couple of sideboards:

Grixis Delver

Noah Walker

Sideboard :

1 Cabal Therapy
1 Darkblast
1 Painful Truths
1 Forked Bolt
2 Pyroblast
1 Ancient Grudge
1 Sulfuric Vortex
2 Baleful Strix
1 Engineered Explosives
1 Pithing Needle
1 Winter Orb
2 Surgical Extraction

Miracles

Joe Lossett

Sideboard :

2 Moat
3 Flusterstorm
2 Back to Basics
1 Pyroblast
2 Red Elemental Blast
1 Engineered Explosives
2 Surgical Extraction
1 Kozilek's Return
1 Wear/Tear

One major advantage of playing cantrips is that it allows you to build a diverse sideboard, and that magnifies the power of your silver bullets. One reason Delver is such an effective strategy is that it has access to a variety of post-sideboard “bombs,” and adding even just 1 copy of a card like Surgical Extraction, Winter Orb, or Price of Progress can swing the game entirely. Noah’s list has a lot of these 1 ofs, but he also has a couple copies of the cards Baleful Strix and Pyroblast because they can come in in a variety of matchups. That way, he is able to first cover a wide swath of the metagame and then judiciously use his remaining slots to play these powerful haymakers. So, if you are playing the full suite of Ponders and Brainstorms, I recommend determining your popular bad matchups and adding some powerful 1 ofs.

Joe’s list has fewer 1 ofs than Noah’s, but he is still focusing more on haymakers. Miracles has a few specific weaknesses game 1, namely Chalice of the Void decks and combo decks because he plays a lot of useless removal. His sideboard has a variety of ways to interact with those weaknesses, and he has determined that Moat is worth 2 slots because it is almost unbeatable if it lands against Eldrazi.

Fair Non-Cantrip Decks

Eldrazi

NoLoam from Magic Online

Sideboard :

4 Leyline of the Void
2 Pithing Needle
2 Ratchet Bomb
4 Thorn of Amethyst
2 All Is Dust
1 Karakas

NoLoam is one of the most successful Eldrazi players on Magic Online and I like how his sideboard is crafted. Eldrazi is a deck with no manipulation, so you need to play more copies of cards to guarantee seeing them. Leyline of the Void is the graveyard hate option of choice for Eldrazi because it is free and the most powerful option for beating decks like Reanimator and Lands. The sideboard cards from Eldrazi also need to be versatile because they are playing fewer distinct cards. So, you see the anti combo catch-all, Thorn of Amethyst.

Death and Taxes

Mack Doyle

Sideboard :

2 Enlightened Tutor
1 Grafdigger's Cage
1 Path to Exile
1 Pithing Needle
2 Containment Priest
1 Ethersworn Canonist
2 Council's Judgment
2 Rest in Peace
1 Gideon, Ally of Zendikar
1 Cataclysm
1 Wilt-Leaf Liege

Death and Taxes

David Baumann

Sideboard :

2 Path to Exile
1 Pithing Needle
1 Containment Priest
1 Disenchant
2 Ethersworn Canonist
1 Leonin Relic-Warder
2 Rest in Peace
1 Veteran Armorer
1 Cataclysm
2 Gideon, Ally of Zendikar
1 Council's Judgment
 Here, two very different sideboard strategies are used for D&T. Mack’s list runs 2 Enlightened Tutors in order to find bomb sideboard cards such as Grafdigger’s Cage and Rest in Peace. This strategy is at its best against unfair matchups where card advantage matters less than card quality. David, on the other hand, opts to play more tutorable threats for his Recruiter of the Guards. His list is better against most fair strategies as he includes more removal and a second Gideon, Ally of Zendikar. Both sideboards are clearly viable, and the one you prefer depends on your metagame call.

Unfair Decks

ANT

Rodrigo Togores

Sideboard :

2 Tendrils of Agony
4 Abrupt Decay
2 Krosan Grip
2 Flusterstorm
2 Echoing Truth
1 Xantid Swarm
1 Empty the Warrens
1 Sensei's Divining Top

Unfair decks are almost universally favored against fair decks game 1 and if they could get away with it, they would simply not sideboard. A deck like ANT only needs a sideboard in order to beat cards that they could not easily beat otherwise, such as Counterbalance or Chalice of the Void. So, you can see Rodrigo’s list packs a lot of answers to the above cards and not much else. His game plan against Delver probably only involves sideboarding 1 or 2 cards because his main deck is already geared toward beating counterspells and discard.

Lands

Daryl Ayers

Sideboard :

4 Chalice of the Void
4 Tireless Tracker
4 Krosan Grip
1 Molten Vortex
1 Ancient Grudge
1 Bojuka Bog

Lands sits at a weird intersection between fair and unfair. It even has some similarities with blue decks, because of the consistency that 8 effective tutors in Gamble and Crop Rotation provide. But in terms of sideboarding, I see it most akin to unfair decks because it only wants to enact its game plan. Most mana bases in Legacy run very few basic lands, and with 4 Ghost Quarters being the new norm, Lands seeks to lock out other decks from casting spells. So, the sideboard cards are there to counter anything that would stop Lands from enacting its game plan. Krosan Grip is a good answer to Counterbalance and Blood Moon, the Molten Vortex helps Lands against Sanctum Prelate, and the Tireless Trackers can serve as a second avenue of victory if your Life from the Loams get hit by Surgical Extraction. Daryl’s sideboard also demonstrates an almost “transformational” plan against a deck like Miracles. He brings in at least 12 cards because Lands’ game plan typically gets trumped by Miracles’. But, with the presence of Chalice of the Void and Tireless Tracker, he has more avenues to power through Swords to Plowshares.

Legacy has far too many strategies for me to go through them all, but that’s part of the beauty of the format. It’s perfectly acceptable to have a “horrible” matchup and choose not to hedge against it. Sometimes, a matchup is so bad that it would take too many sideboard slots to fix, and it’s often better to just ignore it altogether. Legacy is so diverse that you wouldn’t even expect to play against the most popular decks more than a couple of times.

Conclusion

  1. Post-sideboard games are significantly more important than pre-sideboard games. This means that over the long run, fair decks generally outperform unfair decks in Legacy.
  2. Make sure that you have a coherent and effective sideboard plan against the decks you are trying to beat. Put in the time testing your sideboard plans so that you can ensure that they work in practice as well as in theory.
  3. Have a metagame in mind when constructing your sideboard. Depending on which decks you expect, you can vary your options by building a sideboard like Mack’s to hedge against combo or a sideboard like David’s to hedge against fair strategies.
  4. Blue cantrip decks get to play more powerful haymakers because they see more cards in post-sideboard games.
  5. Non-cantrip fair decks should rely on redundancy because there is no guarantee they will have the time to draw the cards they need.
  6. Unfair decks don’t need to sideboard except to beat hate cards.

Thanks for reading

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