Build Guide by Svingas

Preface

1)This guide is meant to give an in-depth description of a particular way to play Sivir.
2)This build is for 5v5.
3)This build primarily focuses on a mid-lane Sivir.
4)Even if this sounds like a crazy build to you, at least try it once or twice before down-voting.
5)Any constructive criticism will be greatly appreciated.
6)Do not simply down-vote because you think Sivir is a bad champion.
7)This is my first build guide, so I borrowed a variety of styles from other guides.

Sivir's Story

The beautiful and deadly champion known as Sivir has been a favorite of League summoners for close to a decade. A soldier-for-hire outside of the Fields of Justice, she is the embodiment of a highly successful mercenary on modern day Runeterra. Sivir has little interest in the ''cribbage sheets'' - as she calls them - of League influence bartering. Instead, she is motivated by material wealth and riches, and she is paid handsomely for her services. Sivir is one of the wealthiest individuals found anywhere on Valoran. Sivir owns multiple residences in a number of different city-states, as well as ownership stakes in a number of businesses all across Valoran. Her detractors, either envious of her success or acrimonious of her flexible morality, have begun to use Sivir as a symbol of what is wrong with the mercenary nature of the League. Sivir dismisses her critics, saying that while her personal code of ethics is less ruthless than her competitors, ''Everyone has a price.''

Sivir has earned many titles and accolades throughout her illustrious career, but the one she held until recently was ''Battle Mistress of Noxus''. Now she is simply known as ''The Battle Mistress'' after breaking her contract with the Noxian High Command. Sivir dared to object to the Noxian war against the peaceful island state of Ionia, though less about the morality of the issue than the planning behind it; her predictions of a bloody stalemate came true when the Ionians held off the relentless assaults of the Noxians. Claiming that the Noxian High Command had lost its direction, she left Noxus and made her services available to the Institute of War. The Noxian High Command has sent a number of contracted assassins to deal with its rogue mercenary, but none have delivered her or survived.

''Time and time again, Sivir proves that she has earned the right to call herself 'The Battle Mistress'.'' -- Jax

Introduction

Welcome to my Sivir build. Sivir is the first champion I bought when I started to play league of legends and since then I have continued playing her as my primary champion. I have worked my way through a variety of different item, rune, and mastery builds in the process. This guide can be helpful to those who have never used Sivir before, as well as those of you who like me use her very often. If at any time, you notice anything missing from my guide, or change because of a recent update, please let me know. I hope you have fun reading and enjoy this guide. If you do please up-vote. I hope to see Sivir being played more consistently in future League of Legends matches. I have made a few slight modifications to my build and am now re-posting it. The primary reason for me re-posting my build is because my old Sivir guide received troll votes and rage votes from people who did not like me commenting on their builds.

Base Stats

Damage: 52.11 (+2.9 / per level)
Attack Speed: 0.679 (+3.1%/ per level
Range: 425
Health: 378 (+82 / per level)
Mana: 203 (+43 / per level)
Move Speed: 310
Armor: 12.75 (+3.3 / per level)
Magic Resist: 30 (+0 / per level)
Health Regen: 4.25 (+0.55 / per level)
Mana Regen: 4 (+0.3 / per level)

Runes

Greater Mark Of Desolation-This is arguably a must have for any high DPS champion. Armor Penetration is very helpful early game when your attack damage is still very low. Armor Pen is also very nice later in the game when you are facing champions with very high armor such as Malphite or Rammus. With runes focusing on armor penetration, as well as the very high attack damage per hit provided by my item build, even tanks can be taken down fairly quickly.

Greater Seal of Evasion-Due to somewhat recent updates to items in League of Legends, there are currently very few items that provide dodge chance. Sivir already has a dodge chance through her passive if she is moving. Therefore, with the additional 6.75% dodge chance provided through runes, late in the game Sivir has a 31.75% dodge chance while moving. As I will get into later in my guide, this should be most of the time.

Greater Glyph of Scaling Cooldown Reduction-With cooldown reduction provided through Ionian Boots of Lucidity and runes, late game Sivir will be able to throw her Boomerang Blade and cast Spell Shield multiple times in a fight. Furthermore, with this amount of cooldown reduction On The Hunt will be ready almost any time you would need it. I choose cooldown reduction per level over base cooldown reduction for two simple reasons. First, cooldown reduction per level simply offers more reduction overall for most games because Sivir levels very quickly. Second, if you use Boomerang Blade too much in the early game you will run out of mana quickly.

Greater Quintessence Of Desolation-The same reason as I gave for Greater Mark Of Desolation. With Marks and Quintessences focused on armor pen, without any items, you begin the game with nearly 25 additional damage per attack. This is helpful for harassing and clearing out minions quickly if needed.

Masteries

For my masteries, I choose to put 21 into Offense and the remaining into Utility. I grab Cripple because if you are going to use the spell Exhaust, Cripple makes it significantly more deadly. I choose to avoid Brute Force and Lethality for the most part because Brute Force provides very little extra damage and the Sivir I build has very little critical strike chance so Lethality does not affect much. In the Utility tree I put four into awareness to level even more quickly. I also put the last point into Utility Mastery so that your Lizard buffs will last a little bit longer.

Summoner Spells

Teleport-This is one of the most valuable summoner spells in my opinion on many champions. Furthermore, it is almost essential to have at least one on a team. As Sivir, if you are going to be midding; in most cases you can easily recall, buy items, and Teleport back to your turret before the enemy mid is able to touch it. This is also a very helpful spell for back-dooring with or without minion support. If minions are pushing down a lane solo and everyone else is occupied, you can Teleport over and kill the turret before the other team can do anything. Also if you did not use your Teleport to get to the turret, you can use it immediately afterwards to rejoin your team. This is better than recall in some cases because damage does not prevent you from using Teleport unless you die. Finally, with Sivir's great ability to wipe out minion waves and hold off a tower until support arrives, Teleport can get you there in seconds.

Exhaust-Sivir has no other way to disable enemy champions aside from items. It is very helpful if you are able to quickly Exhaust an enemy high DPS character at the start of a fight. Furthermore, with Exhaust and On The Hunt, Sivir should be able to win or escape from almost any one on one confrontation.

Note:There are some other summoner spells that work okay on Sivir; such as, Flash and Ghost, but with the item builds I provide, Exhaust is a much better option.

Skill Sequence/Description

Fleet of Foot-At maximum level, Sivir's passive provides her with an additional 25% dodge chance while moving. This is one of the reasons why Sivir should be consistently moving in team fights. This passive is also very helpful when you are running back to safety after destroying an enemy turret because all of their basic attacks have a higher chance of being dodged.

Boomerang Blade-EARLY GAME HARASSMENT! If you use this wisely in the early game, especially if you are doing solo mid, your opponent will quickly learn to stay behind his minions and avoid engaging. One of the biggest mistakes I see with people playing Sivir is that they use Boomerang Blade to try to kill minions too early on. This is just a waste of mana. Any time that you have Boomerang Blade available you should be looking for an opportunity to hit the enemy champion directly. This ability is also very useful when you are pushed up to the opponents turret. While they are there killing your minions; simply run up, throw your Boomerang Blade and run back before the turret can focus you. I do not start using Boomerang Blade to clear out minion waves until I have a Manamune at the earliest.
Late game, Boomerang Blade has a few different uses. The first thing to make note of is the fact that this ability does magic damage, as do most abilities. However, this is significant because Sivir does not really have any other magic damage unless you happen to purchase Madred's Bloodrazor. In a team fight, you should almost always be either using Boomerang Blade or waiting for its cooldown. This is a very good way to greatly damage or kill the enemies squishy targets without having to come very close to the battle. This can also be very effective in attacking champions who only have armor, but very little magic resist. Often, I will throw my boomerang blade at the tanks later on in a fight after the squishies have been taken care of.

Ricochet-This is a way to harass your opponents without even trying early game. This is also the ability that will allow you to wipe out an entire team simultaneously late game. I have gotten penta-kills simply from basic attacking with Ricochet on and maybe one Boomerang Blade. Some people emphasize the importance of stacking attack speed on Sivir because of Ricochet. The problem with this is that Ricochet costs mana per hit and the higher your attack speed early game, the faster your mana will be drained.

Spell Shield-This is the ability that sets excellent Sivir players apart from all the rest. You will notice in my skill sequence that I take one level of Spell Shield before leveling up everything else. The reason for this is that the only difference between levels is the length of the cooldown, which is nice to bring down, but leveling up the other abilities is more important. This ability is extremely important in the laning phase. FREE MANA! Many people tend to overlook this aspect of spell shield; both those who play Sivir and those who play against Sivir. Spell Shield costs 75 mana, but if it blocks an ability, you then restore 125 mana. This is the primary way that I keep my mana up early game. This ability also works great in conjunction with Boomerang Blade. When you see an enemy champion coming towards you to use an ability, you immediately activate Spell Shield and then throw Boomerang Blade. This not only negates the ability the enemy champion just attempted to use, but often the enemy champion is committed to the point where they get hit by the Boomerang Blade going both ways. The other way that Spell Shield is huge early game is in the situation of being ganked. I hardly ever get ganked, even if I am pushing all the way up to the enemies turret. As soon as you see the ganking enemy champion coming into your lane, immediately activate Spell Shield and run to your turret throwing Boomerang Blade in the process. This also greatly discourages future ganking attempts, and I have also gotten several kills because the enemy attempting to gank over-commits.
All of these applications of Spell Shield are fairly simple and automatic. (If "blank" happens, respond with "blank.") Late game is where you will have to spend time getting used to when exactly you should activate Spell Shield. A good basic rule is that if you are about to run into a fight you activate spell shield. Other than this, you have to recognize when a champion has actually committed to using an ability on you and react very quickly. Otherwise you will just activate Spell Shield to early; in which case, the enemy will simply wait until it runs out and then attack you while it is on cooldown.


On The Hunt-My description for this ability is much more simple than for the above abilities. Three main uses: any large team fight, immediately activate On The Hunt; if you are backdooring and attacking a turret while everyone else is occupied, activate On The Hunt; and if you see a few of your allied champions are trying to escape a fight with enemies close behind them, activate On The Hunt, run up to your teammates, and run back with them.

Note:Other obvious uses for On The Hunt are if you are fighting Baron and possibly if you are soloing Dragon.

Items

I start with a Meki Pendant, a Health Potion, and a Mana Potion. I start with the same three items whether I am going for mid or for a side lane. 99% of the time, as soon as you hit 605 gold you want to recall back to base and buy a Tear of the Goddess so that you can start building up mana and so that Teleport will be ready when you are ready to go back for more items. I very rarely get forced out of lane.

Note:When I am mid I usually focus on getting Manamune as quickly as possible so that you can take out entire minion waves very quickly. Also if you play somewhat defensively in mid, you will not need boots before you have enough money.

Note:If you are in a side lane, especially if you are 1v2 you will probably need to grab the Vampiric Scepter early to keep your health up.

Note:If you play defensively and do not overuse abilities, you will only need the single Health Potion and Mana Potion.
The Bloodthirster-This is where the game starts to take off very quickly. Thanks to Sivir's ability to take out entire creep waves with one Boomerang Blade, you can quickly rack up the additional 40 attack damage, and 10% lifesteal.

Note:Once you purchase and fill your second The Bloodthirster you already have an additional 200 attack damage and 50% lifesteal.

Note:The very significant damage boost and lifesteal provided by The Bloodthirster makes it the core of this build. Boomerang Blade now gains additional damage based upon (.95)x(Bonus attack damage). Furthermore, a reason I focus on attack damage over attack speed for Sivir is because attack damage is the most significant stat that affects Ricochet. Any on-hit effects only apply to the first target hit. On The Hunt alone provides Sivir and her teammates with a significant attack speed boost.
Trinity Force-75%-90% of the time this will be my fifth item. It is simply one of the best options for a typical DPS champion. It provides a moderate boost to a number of different stats, along with a 25% chance to slow the target.
Frozen Mallet-There are always those games where you are having very little difficult staying alive or winning fights. However, the annoying thing is all those champions escaping with very little health. With the Frozen Mallet in conjunction with On The Hunt, you should be able to chase down most fleeing enemies. Plus, who is going to complain about an extra 700 health.
Banshee's Veil-Every once in a while you face a team with a ridiculous amount of magic damage and immobilizers. If you are having one of those games, where you are still getting stunned continuously even though you are blocking abilities with your spell shield, this would be an item to consider.
Infinity Edge-If you are having absolutely no issues with dying and you simply want a ton of damage this is the item to go for.
The Bloodthirster-My preferred item. An additional 100 attack damage and a total of 75% lifesteal. If the other team is not able to bring you down in the first couple seconds, you alone can decimate their team.
The Black Cleaver-If you are not having much trouble staying alive, but at the same time you are having difficult actually killing the other champions as well, this item solve the problem. I would choose this item over Last Whisper if you are facing a mix of tanks and squishies.
Phantom Dancer-If you are having a game where you are not really needed in the team fights, and everyone being fairly passive, this is the item to go with. While everyone else is in the middle throwing in little jabs, but not really doing much you can go around and take down turrets in seconds and then run back before the other team can cut you off.
Madred's Bloodrazor-I personally do not get this item very often because it is expensive, and in most cases a third The Bloodthirster just works better. However, it is an option if the other team is stack a lot of armor and health, but no magic resist.
Trinity Force-This is only if you chose to buy a different item for your fifth item, such as a Banshee's Veil.
Frozen Mallet-If you find yourself needing just a little bit more health and you are still having issues with champions escaping after getting a Trinity Force, this can be a good last item.
Last Whisper-As I briefly alluded to above, I would only get this item if you are facing a team where at least three or four of the champions are stacking armor.
Wit's End-If you find yourself against an army of mages, this item could be very helpful. It provides a little extra magic resistance and you can use it to drain away their mana. (A manaless mage is a dead mage.)

General Gameplay

Early Game

During the early game, I usually take on a more defensive play-style in order to stay in lane as long as possible and chip away at the other champion. By playing this way, I am usually able to either for the enemy champion out of lane multiple times without having to return myself, force the enemy champion to turret hug getting gold deprived, or rack up a couple kills when they underestimate the damage of Boomerang Blade.
I do not worry about hitting the turret myself unless the enemy mid leaves to try to interfere with a side lane. If you have Manamune, On The Hunt, and a wave a minions; you should be able to take out the first mid-lane turret if the enemy champion is foolish enough to leave you alone mid to help out with a side-lane. As I described above, the particular order for my first three items, depends entirely on the game. The only concrete, constant is Tear of the Goddess at 605 gold. I usually find that I have enough gold to return to base and purchase my second set of items after Tear of the Goddess by the time my Teleport is ready.
I spend the majority of the laning phase between my turret and the middle of the lane. By doing this, the only way for the enemy champion to come out and get minion kills without getting attacked by the minions is to come within range of Boomerang Blade.

Mid Game

Once I have my first The Bloodthirster or at least the B. F. Sword, I play more offensively in order to push over the middle turret if I haven't already. At this point I begin to run to other lanes and usually my team is able to push over the side turrets without much trouble because of the 3 people in the lane and the fact that I can harass the enemy champions if they try to stop us from attacking the turret. However, I only go to other lanes to help out if my Teleport is on cooldown, or if the minions are pretty close to the second middle turret. All the while, I am farming as many minions as possible, including those in the jungle. I also usually try to grab the Lizard buff unless my team has a very possessive jungler.

Note:Sometimes you have to go to help out with other lanes simply because your teammates are having trouble holding their lane.

Late Game

If the game has actually lasted this long, after you have gold deprived their mid who likely should be their carry, this is when Sivir gets extremely fun to play. At this point you will already have at least two of The Bloodthirster and you might already be pretty far along with your fifth item. I have found that most of the time when I play, my teammates do not really feel like running back and forth between lanes to push back encroaching minions waves. I am perfectly fine with taking this job. Sivir can easily dispact 20 or more minions with one Boomerang Blade and a few attacks with Ricochet bouncing all around. What this means for you is that you will reach level 18 very soon, and you will also be able to finish your build soon.

Team Fight

There are a variety of different ways that games play out once you get past the 40-45 minute mark. Sometimes there are just pretty consistent team fights. For these it is important to understand your role. This is where you having to be very active and make good use of your spell shield. If you are able to wait a second or so after the team fight start before activating On The Hunt and joining, this is ideal. Focus on the squishies with your Boomerang Blade and basic attacks, and let your Ricochet handle the rest. This is especially important if you are fighting a Rammus with Defensive Ball Curl or anyone with Thornmail. As long as you do not directly attack the champions with these items, you can damage them with your Ricochet without taking any damage from the effects. Once all of the squishies have been taken care of, you can then easily take on these champions head on.

Back-dooring

The possible option is for you to begin back-dooring, which is something that Sivir excels in over most other champions. Usually I choose to back-door with minion support, which some do not consider back-dooring, but you are still attacking the enemy on you own from a different direction than that which they are focused on. If you have noticed that both teams have just been pushing back and forth slightly in one lane without doing much, and your team is having no trouble staying alive playing defensively. This is a prime time for you to break away and push down a side lane to a turret. If nothing else, this will draw away one or two of the character from the other team, and then your team suddenly has a slight edge. However, there are also times when you team will just yell at you if you are back-dooring when you are needed elsewhere.

Note:Your teammates may expect you to be in charge of warding Baron and Dragon because you will probably make the most gold on your team. Whether you have to do it or someone else on your team does, it is very important to keep Baron and Dragon warded.

Note:Once you have your first The Bloodthirster, you can solo Dragon, but you will need the help of On The Hunt. Once you get your second The Bloodthirster you can solo Dragon without any problems. Keep this in mind and try to kill Dragon as soon as he re-spawns if possible. This is great for everyone on your team.

Match-ups

Akali-Despite her being melee, she will sometimes take mid if there is not a better mid on the team. She is very easy for Sivir to take care of. Simply Spell Shield her Mark of the Assassin and out-push her, throwing your Boomerang Blade when you see an opening even if she goes into her Twilight Shroud.

Anivia-Due to a recent update, it now costs significantly more for Anivia to quickly turn her Glacial Storm on and off in order to kill a minion wave. Because of this, you should have no problem keeping the fight near the middle of the lane. Her Flash Frost is very easy to Spell Shield because it comes at you very slowly.

Annie-The main thing to focus on with Annie is her ability to stun you. Pay attention to when she has reached the point where her next spell will stun. You can see a small swirl around her. This is not to be confused with Molten Shield, which is an orange bubble around her. Be sure to activate Spell Shield if you see Disintegrate coming towards you. It is very important to harass her with Boomerang Blade consistently so that she cannot just sit back and farm.

Ashe-I hardly ever come close to running out of mana when I face an Ashe. When she fires her Volley, it is very easy to activate Spell Shield and situate yourself to get hit by one of the arrows. If you see her fire Enchanted Crystal Arrow, try to warn your teammates.

Caitlyn-I have found this champion to be the most difficult for me to counter as Sivir. She can very easily out-range you so that it is difficult to go in for last hits. Try to stay pretty close to your turret most of the time and use Spell Shield whenever she fires Piltover Peacemaker. however, you need to stay far enough away that she cannot shoot your turret with her long range. Once you get your first The Bloodthirster, if you are still in the laning phase, she will not be much of a problem. If you need free mana, activate Spell Shield and run over her Yordle Snap Trap.

Cassiopeia-You want to prevent her from being able to effect both you and your minions simultaneously with her aoe poison, so this means usually staying a few steps away from your minions. Cassiopeia is one of the most frail champions early on so harassing her with
Boomerang Blade can quickly force hher to be defensive.

Corki-It is very easy to Spell Shield both Missile Barrage and Phosphorus Bomb. Anytime he uses Gatling Gun, just back away until it runs out. Corki has a pretty long range, so he can definitely out-range Sivir with basic attacks.

Ezreal-I usually play fairly defensively here. Ezreal can quickly jump to you with

Arcane Shift and follow it up with his other abilities. If this happens you have to be very quick to activate Spell Shield. Similar to if you are facing Ashe, warn teammates if you see him fire Trueshot Barrage.

Fiddlesticks- Dark Wind can be very dangerous because it will prevent you from using your Spell Shield or Boomerang Blade if you get hit. If you get silenced, simply back up a few steps until it goes away. When you see Fiddlesticks using Drain, throw in your Boomerang Blade and it might be enough for him to cut it off early.

Galio-I have only played against a Galio mid once or twice. Just keep in mind that he can slow you with Resolute Smite, as well as speed himself up with Righteous Gust, to chase you down very quickly. If you are able to Spell Shield Resolute Smite, this becomes a non-issue.

Heimerdinger-If you play smart, you are able to take out his H-28G Evolution Turret without putting yourself in any danger simply with Ricochet. Also, do not be afraid to focus directly on his H-28G Evolution Turret with your Boomerang Blade. It is worth the mana to take these turrets out quickly, and sometimes Heimerdinger will even stand right next to them, so you damage them both significantly. Save your Spell Shield for any time you see his ch-1 concussion grenade coming toward you.

Karma-At this point, I have not played any games against Karma mid so this will be updated once I have first-hand experience. One pointer is to avoid over-committing when she is low health, because Soul Shield provides a significant shield and she can also slow you under her turret with Spirit Bond.

Karthus-If you are having trouble with avoiding his Lay Waste, stay close to your minions because it does significantly less damage when it hits multiple targets. Also, you can consistently regain mana by activating Spell Shield on top of Lay Waste. Most importantly, you can completely negate his Requiem against you with Spell Shield. Warn your team when Karthus reaches level 6 so that they know he can use Requiem now.

Kassadin-At level one, you should play very defensively because in most cases Kassadin takes Null Sphere at level one. There is nothing you can do against this and it hurts a lot, so if you let yourself get hit a few times you may have to recall early. Once you hit level two, it becomes very easy to activate Spell Shield to make Null Sphere useless. Once Kassadin hits level 6, Riftwalk just gets annoying. You have to have very fast reflexes to see when he is about to Riftwalk and back up quickly and use Spell Shield if you have it.

Katarina-This is another melee champion that make take mid. Play defensively so that most of the fighting is near your turret and use Spell Shield and time you see her Bouncing Blades bouncing toward you. You do not have to worry about her hitting your turret much at all even with a full wave of minions there because you can throw Boomerang Blade to hurt her and scare her away. Never underestimate Death Lotus. Remember you are frail.

Kennen-In most cases, very frail at least in the early game. Your Boomerang Blade will take a large chunk of his health each hit. When Kennen uses Lightning Rush I usually run back a few steps so that he chases and then activate Spell Shield before running into him and firing off a point black Boomerang Blade and a couple basic attacks. When he uses Slicing Maelstrom, just get out fast.

Kog'Maw-Focus on last hitting and keeping the fight near the middle. Once Kog'Maw reaches level 6 you will have to start dodging Living Artillery fairly often. When Spell Shield is available, use it. When it is not, move around a lot.

LeBlanc-The main danger here is Distortion. Usually she will return to her original position before you can do much damage to her, but activate Spell Shield when you see her about to use Distortion. If you are able to fire off a Boomerang Blade, there is a possibility of hitting her an additional time.

Lux-Focus on last hitting and playing defensively. Spell Shield any time you are in her Lucent Singularity, as well as if you will be one of the two targets hit by Light Binding. Usually, by staying behind minions, this is not an issue.

Malzahar-Unless you can get the upper hand early, you will probably be near your turret most of the time until you get Manamune and possibly Vampiric Scepter. Stay away from any minions afflicted by Malefic Visions because it could jump to you. Call of the Void allows for plenty of time to activate Spell Shield so just hold onto Spell Shield until he uses Call of the Void.

Miss Fortune-She can clear out minions very quickly with Make it Rain. Just stay out of the circle and hit her with Boomerang Blade if you get a chance. After Make it Rain ends, then move in and kill the minion wave. You may be near your turret often against Miss Fortune.

Mordekaiser-I have had to mid against Mordekaiser a fair number of times and Iron Man is just annoying. Consistently harass him to keep his shield low or empty. This also forces him to use other spells to refill it such as, Mace of Spades or Siphon of Destruction, which you can use Spell Shield on to regain mana.

Morgana-Always get out of Tormented Soil as soon as possible. Morgana will often use Dark Binding follwed by Tormented Soil if you are without minion support under your turret. Quickly use Spell Shield to avoid the snare and then you can just walk out of Tormented Soil. This also causes her to waste mana. Do not waste your mana by throwing Boomerang Blade when she is using Black Shield if possible.

Nidalee-She is rarely in mid, but when she is she can be annoying. Javelin Toss deals more damage the farther away you are, so if you are very far away it hurts a lot. This is what you want to focus on with Spell Shield. Javelin Toss moves very slowly so it is easy to see coming. I rarely see her use Aspect Of The Cougar in mid to come after a champion.

Pantheon-The combination of Aegis of Zeonia and Heartseeker Strike is very dangerous. As long as you activate Spell Shield before Aegis of Zeonia, you can quickly move out of Heartseeker Strike and also hit Pantheon with a Boomerang Blade. Otherwise, just farm away and harass him consistently.

Ryze-I will have to play against the re-structured Ryze a few games before I can give a good counter-style. He relies heavily on spells, so you will rely heavily on Spell Shield.

Sivir-The most annoying thing in my opinion, is to lane against another Sivir. Keep in mind that she can dodge your first swipe of Boomerang Blade and run back into it with Spell Shield for free mana just like you can. Therefore, you have to judge the reflexes of the other Sivir and be very accurate when you choose to throw Boomerang Blade. Try to avoid her Ricochet bouncing around. If you get stuck under your turret without minion support, be very careful about her Boomerang Blade.

Swain-One of his best abilities Nevermove can be made pretty useless if you can react quickly with Spell Shield. This is his best ability in my opinion, so if you are able to prevent him from rooting you, you can play pretty offensively. Be careful when Swain uses Ravenous Flock, but do not be scared away. I usually cause him to actually lose health by the end of Ravenous Flock with Boomerang Blade.

Teemo- Boomerang Blade takes away a huge chunk of Teemo's health right away. you can last hit pretty easily because Teemo only has 500 range, which is less than most other ranged characters, but it is still higher than Sivir. Any time you see Blinding Dart coming, use Spell Shield. If you see Teemo "use" camouflage and go invisible, throw your Boomerang Blade directly at him. It is usually good to invest in an Oracle's Elixir if you are midding against a Teemo because you will see him when he is invisible, and your Ricochet will kill his Noxious Traps.

Tristana-Her range can be a significant problem because it starts at 550 and continues to increase each level. Luckily, with Ricochet you are able to still compete with her range with the bounces. It is very important to use Spell Shield when she uses Rocket Jump or Explosive Shot. You need to work hard to harass her with Boomerang Blade or she can just farm freely.

Twisted Fate-Luckily you can use Spell Shield to block Pick A Card, especially if he uses gold card. However, Pick A Card has a very low cool-down so you have to be defensive. If Twisted Fate stops using Pick A Card on you because you keep using Spell Shield, you still have an opportunity of regaining your mana by allowing yourself to get hit by Wild Cards. Warn your teammates when Twisted Fate reaches level 6 so that they know she can use Destiny now.

Twitch-An Oracle's Elixir is almost necessary if you are mid-lane against a Twitch. Otherwise, he can move around behind you and kill you before you even get close to your turret. You will want to play very defensively regardless, because deadly venom[[ makes his basic attacks very dangerous. The good thing is that [[twitch is very very frail.

Urgot-Avoid getting hit by his basic attacks because with his passive Zaun-Touched Bolt Augmenter they cause you to do less damage. The good news is that you are finally against a ranged character with a smaller range than you. Focus on avoiding Noxian Corrosive Charge with your Spell Shield. Be careful not to get extremely close to his turret because he can use his Hyper-Kinetic Position Reverser to switch places with you and put you under or behind his turret. Focus on killing minions and avoiding his Noxian Corrosive Charge. He may block the damage from Boomerang Blade sometimes with Terror Capacitor, which provides him with a shield.

Veigar-Extremely frail! At level nine, if you hit him with your Boomerang Blade going both ways, it will most likely take him below half health. Veigar should focus on last hitting minions with Baleful Strike in order to build up his AP, which allows you to farm freely. Once he gets to level 6, be careful of Primordial Burst, which does a significant amount of damage even at low levels.

Vladimir-Thanks to a recent update in League of Legends, Vladimir is somewhat less dangerous. Most of the time he will learn to avoid using Transfusion on you because of your Spell Shield and will start to focus on minions, but if not enjoy the steady mana. Vladimir is fairly easy to harass with Boomerang Blade and Ricochet because his range is the same as yours (450).

Zilean-He has a long range and his Time Bombs are annoying. Most Zileans will quickly learn to avoid placing their Time Bomb on you and will place it on the minion right next to you so that you cannot use Spell Shield to block it and you still receive damage. Personally, I recommend still using Spell Shield when you see him about to place a Time Bomb just to be safe unless you are having significant mana problems. Zilean has low maximum health, so it is important to harass him as often as you can with Boomerang Blade. Because of his Time Bomb and long range, you might be under your own turret most of the time, but this is fine because he does very little damage to it.

Note:This does not address every champion in every situation, but it covers the majority.

Teammates

I have mentioned multiple times that Sivir is pretty frail. Because of this, you want to have at least one tank and one other tough character on your team. The reasoning behind this is that if your team is made up of entirely frail characters, you will very likely be one of the top priorities because of your high DPS. However, if there are a few other tough characters on your team, they can keep enemy champions occupied while taking the majority of the hits. I usually prefer to have only one other frail character on my team in most cases.
Also, it is good to have teammates with crowd-control abilities because Sivir has not ability to disable aside from items. Some great options for crowd-control would be Amumu, Blitzcrank, Cho'Gath, Heimerdinger, Lux, Malphite, Nunu, and Shen.
Finally, it is always a good idea to have at least one person on your team with a global ability if possible.

Who To Focus In Team Fights

It does not matter if the tank has 1/3 health and the rest of his team has over half health, do not focus the tank. Especially as Sivir, you can just let your Ricochet take care of that. Almost always focus on the most frail champion because even if this champion is not doing the most damage, by killing this champion, the enemy now has one less champion doing damage. It is also good to focus-fire anyone who is able to able to damage multiple champions on your team at once. Lastly, if there is somebody on their team who has been absolutely destroying your team in every fight, try to get them out as soon as possible.

In Team Fights These Champions Should Be "Shot On Sight"

Akali
Anivia
Annie
Ashe
Evelynn
Fiddlesticks
Katarina
Kennen
LeBlanc
Lux
Malzahar
Master Yi
Ryze
Shaco
Sivir
Teemo
Twisted Fate
Veigar
Warwick

Note:It is important that you discuss with your team prior to getting into a team fight, who you are going to focus first if you are facing more than one of these champions.

Pros / Cons

Pros

-Extremely high damage to multiple targets
-Excellent farming ability
-Able to take down towers alone in a matter of seconds
-Able to chase down most fleeing enemies
-High dodge chance when mobile
-Able to drastically change the outcome of team fights if handled correctly
-Very capable counter to most mids
-Able to maintain full health most of the time due to lifesteal
-Wins almost any 1v1 fight

Cons

-If you allow yourself to be focus-fired, you are dead in seconds
-Relies heavily on spell shield, which can be hard to master
-Requires a defensive play-style
-Almost always a main target
-Few escape tactics
-Tough early game

Conclusion

This guide will remain a work in progress. As League of Legends continues to go through updates, sometimes strategies need to change to compensate. I will be consistently checking for feedback, updates, and ways to improve my guide. My primary purpose for creating this guide is to change the image of Sivir. Many players consider Sivir to be a weak player and refuse to even try her. I have found that with the right items and strategy, Sivir can be an extremely dangerous champion in any game. I have spent days constructing this guide, as well as months playing Sivir. This is a long guide and it can take a while to read, but do not let that be a reason to down-vote my guide. Try it out a few times and experience the results first-hand.
While creating this build, I looked through each of the top rated builds to observe the style that they used. Therefore, I want to thank those of you who have created those high quality guides as an example. I would also like to thank my roommate, who first suggested the idea of trying multiple Bloodthirsters on Sivir to me.

"The hunt begins."