It has come to my attention that many decks on this website have no idea what they are doing with their sideboard. So I am doing a massive write up in the form of a deck so that maybe one or two people will learn.
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Why have a sideboard
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do you have one deck that your friend has that you hate and have a bunch of cards in your favorite deck just so that his deck doesn't work? Even though your deck doesn't run quite as smoothly with these cards in it? Those are the cards that run in a sideboard. With the sideboard you have a powerful tool to nullify your bad matchups. You want your deck to run the best it can possibly run the first game in a set of three, because you won't always be playing that one friend with the annoying deck. However when you are playing him, thats when your well made sideboard saves the day by allowing you access to the cards that completely shut down his deck.
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TL;DR -- why to make a sideboard
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shut down annoying decks without sacrificing playabillity against every other deck in the world.
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How to use a sideboard
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to look at how to use a sideboard, I am going to use the deck with the highest game 1 win percentage in legacy, dredge. If you have never seen a dredge deck play, it is an experience that you should get at one point, but let us suffice to say its very relient on the graveyard. It is very fast, and very consistent. It will easily win on the first few turns of the game left unchecked, which is why it has such a high game one win chance. However, here is where having a sideboard becomes very important.
Many legacy players board graveyard removal in their sideboard just to help them against the dredge matchup. Things like tormond's crypt and relic of progenitus are used to destroy the dredge decks graveyard base, and therefore prevent them from winning.
Then how come everyone doesn't play graveyard hate in their main deck, if dredge is such a powerful deck? Simple, legacy is very diverse and most of the matches you play, or maybe even all of them, will not be against dredge decks. In fact there are enough decks in legacy that if you had a main deck answer for every one of them, there wouldn't be any other cards in your deck left to win the game! This means that a well built sideboard becomes invaluable to success in any tournament, or possibly casual, play.
For the purpose of explaining this better, i have put the most popular deck in legacy below, it is a merfolk deck. This deck is very fast and revolves around powerful creatures and powerful lords as well as being able to play good counterspells, such as force of will. (credit for the merfolk deck goes to Maxwell Jacob with his deck that won the starcitygames tournament in indianapolis on 6/5/2011)
Now to explain the sideboard, yes there are no ways to deal with dredge, but maxwell apparently correctly decided there wouldn't actually be enough people playing dredge at this tournament for him to have to worry about it, but i will explain the sideboard the best i can figure, given there are several choices i would consider interesting.
note, i did not create this deck, so if anyone has different theories on why he chose the cards he did, feel free to share them
Pithing needle is a great sideboard card that is a good catch-all, it is similar to phyrexian revoker, but its not a creature. Playing this card will be a good way to get around enchantments or other cards with annoying abillities.
Llawan, cephalid empress, is a card used to stop merfolk decks. This deck generally makes up about 10%or more of the legacy meta-game (or what deck people choose to play). This is an interesting choice for a merfolk deck, but hey, this guy won with it so it obviously did something well
Back to basics is good vs almost any legacy deck. With a few exceptions (such as merfolk) legacy decks are highly dependent on their dual lands. Cards like tarmogoyf(sorry if i spelled it wrong) run in almost any deck from the dual lands that allow them to function. By taking away these you are dealing a huge blow to their mana base. I think this may have been more specifically used to counter a deck like coutnertop, where the creature of choice is the famous tarmogoyf. I don't know what the meta game looked like at this event, but that is what I think might have been the reason anyways.
Dismember is good creature removal. I think this card might have been for any creature deck with a good sized attacker. You can appreciate cards like these in particular for sideboards because of the sheer number of decks that they work against. Its like boarding cards that are hate for most legacy decks. every card so far, with the exception of empress for the ever-present merfolk armies, has targeted not one, but many decks.
submerge targets most likely tarmogoyf specifically. Its a free tarmogoyf removal to the top of an opponents deck, which is important when you want to kill them pretty darn fast.
Umezawa's jitte is an amazing equipment card. period. It is better than the swords standard loves and always will be in my opinion, it just plays a bit of a different role. Here I think the target is zoo. Zoo is basically lets get out a bunch of very cost efficient creatures, such as wild nacataal, and then use dual lands and other means to beef them up to full size, and win. It is a very strong aggro deck and it has a good matchup vs merfolk. I believe the umezawa's jitte are included to help soften up this advantage, as it is a great method for delaying and beating the opponent. Heck the thing does about everything you would want it to in this matchup, beefs up your creatures, weakens their creatures, or gains you life!
so yeah, by using the sideboard, the player is much better prepared for facing any deck in their metagame
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TL;DR
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board hate to stop lots of annoying decks relevant to your meta game, keyword being LOTS
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What not to do
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The sideboard is not an extension of your deck to make it run better. if your deck runs better with a certain card, it should be main deck and something else should be out. All too many times i see people putting things in their sideboard that actually need to be in their main deck, or just are flat out useless. Use your sideboard well and it will reward you.
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TL;DR
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.... you can read one measly paragraph i think
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Anyways, if anyone has any comments or opinions, feel free to share, I am going to bed now but will check tomorrow at some point if anyonehas any questions. I just hope maybe one person learns to sideboard better from this huge amount of text.