Pros
>Epicly Fast
>Massive Damage
>Really capable chaser (Ghost, Highlander, Alpha Strike..)
>Rapist.

Cons
>Super uber squishy Early-Mid Game
>Really vulnerable to Snares and Stuns
>Dies fast when focused. Reliant on tanks to soak the damage.

The Pros far outweight the Cons, you're a rapist man..

So this is my first build, and this is how I play Yi. I know a lot of people will start calling 'NOOB CHAMP NOOB CHAMP!' but they dont appreciate the effort and common sense you have to use in the beginning of the game to become the unstoppable beast you are in late game :D Master Yi is very versatile, he can be an assassin, jungle roamer and an epic pusher. You just need the sense in the beginning to get to be the UNSTOPPABLE #1 CHAMPION >=)

VOTE A COMMENT PLEASE :)

Marks: Important, + crit chance is good for Yi becuse his crits do about 700ish.
Seals: Mmm, yeah + dodge is probably the most suitable. Nothing else really works.
Glyphs: You dont even need them =.= CDR is the only glyph that is half decent. Dont waste your IP on glyphs.
Quint: You can either do + movespeed or + flat HP. Dont get HP/Level.

In this order is what you want to by:
>Boots of speed, Health Pot x3
You need to start with boots so that you can chase the enemy when they realise they have no health left :) Enemies dont usually get boots for first item so you will always be faster than them.
>Berzerker Greaves
Best set of boots for Yi, he needs attack speed early, and dont be afraid to change them out for Boots of Swiftness in Late Game.
>Dagger x2
Cheap and early Attack Speed for your killing pleasure, the earlier you get these the faster you become unstoppable!
Zeal
Builds in Phantom Dancer, provides the extra Move Speed which will make you again, faster than the enemy because by this time they will also have boots.
>Cape
+Crit Chance, crits are essential to deal high damage, fast.
>Phantom Dancer
Your standard Melee DPS item, provides lots of Attack Speed and +8% Movespeed so that you can kill them that much quicker!
>BF Sword
It is very important that you dont recall or die inbetween buying the Phantom Dancer and the BF Sword. This is because you need it ASAP. If you get low HP, just jungle the Small Golems, Wolves and Seiths so quick jungle gold. And farm those huge minion mobs with Alpha Strike.
>Infinite Edge
Makes your Criticals hit 250% instead of 200% and gives you heaps of sweet Attack Damage.
>(Only if you are making a lot of gold) Bloodthirster
I say only if you're making lots of money because you need the Frozen Mallet more than the Bloodthirster, but having the Bloodthirster first gives you a lot of staying power, which means you can stay out in the field longer and make lots more money.
>Giants Belt
+420 HP, nuff said.
>Frozen Mallet
Gives 700 HP!! And the 35% On-Hit-Slow is a cherry on top of the chocolate cake :)
>Thornmail
If you're vsing hard hitting enemies, Thornmail makes them hit themselves when they hit you ^^ +50 armour also.
>Phantom Dancer (By this stage the game should be finished but if not..)
After this item, you can kill anything in about 5 seconds of straight hitting.

More Damageeee >:D

And after this Item, you cant die.... (If you bought Bloodthirster before then dont buy this one, obviously you have no room ^^

So first of all, lets take a brief look at Master Yi's abilities (More indepth later):
Alpha Strike: Basically, this attack lets you aim at one enemy, and it runs to that enemy, then to up to 3 more enemies and back to the first one. It is great for three reasons and they are (1) farming minions (2) harrassing in very early game and (3) chasing those enemies who have boots of swiftness.

Meditate: Ok so this is your basic heal ability. It's not VERY useful, but it does allow you to heal slightly when you need that little bit of extra health in the jungle and can't afford to go back to base.

Wuju Style: This is your primary ability to be used in conjunction with your ulti and Alpha Strike. With each level, it increases your base damage by 30/35/40/45/50. Very important to level it as soon as you can because it is what makes Yi great in early game, without it, youll hit low and take longer to kill enemies (resulting in death by turret, or them turning around and killing you). While active, this ability doubles it's effect but while on cooldown has no effect, so you need to know when to use it.

Highlander: Best ulti in the game apart from Ashe's :) Highlander improves your movement speed, attack speed and makes you immune to those deadly slowing moves dished out on you by group attacks. It's used mainly when chasing a low hp enemy in mid game, and chasing anyone in late game, but is also an insanely good escaping ability. Master Yi is not good at defeating groups of more than 2 enemy champions on his own. An added bonus is that, if you kill an enemy champion while this ability is active, all of your abilities cooldowns cancel and you can use your spells again.

So you see, Wuju Style is your main ability and should be maxed out first. Alpha Strike is next, and Highlander whenever possible. Meditate is useless :)

Right now youll just want to be farming minions to get as much exp and gold as possible. Harrassing is not really necessary unless your opponent is a meat-head and is trying to melee you. If you're laning against a ranged character such as Ashe or Annie, just dodge their attacks and ignore them. If you must, you can cast an Alpha Strike on a minion close to them and you will damage them slightly as a way of saying 'Go home, I dont want to have to kill you ^^'. Farming minions should consist of Alpha Striking them when you're alone and normal attacking the weaker ones to get the gold. Early game Yi is very squishy and just makes average hits so you dont want to sacrifice the minion killing for a slim chance of killing a champion. It is important to stay for as long as possible in your lane before going back to avoid missing out on last hits. Try for those early kills to quicken your leveling and item buying, but just remember, dont die or you're feeding the enemy!

This is where Master Yi is either make or break depending on how many minions you killed and got gold out of. By level 4, you should easily have your Berzerkers Greaves and should probably even have your first Dagger to make up the Phantom Dancer. People who are too slow will have a ****py mid game and will die too much, but never fear, you can still make up for that!
So mid game strategy...You're going to want to start killing champions by bout level 6 because your ulti is such a 'HOLY **** THATS SPEED HACKS @$%#%^' ability which makes your speed very fast. This is how you attack in mid game:
-Gank from behind your enemy, so they have a longer distance to retreat with you bashing on them.
-From the bushes, start running and activate Highlander (R)
-Exactly after doing this use Alpha Strike to get close to your enemy
-And exactly after doing that activate Wuju Style.
If you commit to this attack, even if the enemy is a tank, you will always kill him if you have full health.
Its not that the enemy CANT beat you, its more that they get scared and run, giving you that extra time to hit them without being hit.

You're a rapist man =\ By the time you hit level 10, everyone else should also be level 10 or 11. But dont worry, this is normal! In this time, you should be harrassing as many champions as possible by helping your team who might still be laning to dispose of the champion in their lane so that they can push down a tower or so. You shouldnt be sticking to a lane, you should be owning the jungle to stop any of the other casters such as Evelynn or Melee DPS's such as Jax roaming around.
This is when you can cause the most damage, before everyone turns level 18. You need to pick out the most strategic champion to kill, and by level 10 you should have the Frozen Mallet, and if not atleast the Giants Belt, so you dont have to worry about turrets because you can run right past them and they would only take down maybe 1/8 of your health.
A common mistake people like to make about late game Yi is that he's still very squishy when it comes to turrets. So when they have low health and need to recall, they go and hide behind the turret. WROOOONG! This is where you come in, as I said earlier, activate Highlander and Alpha Strike that silly person. You can stay for as long as you want to kill him because the turrets do not do that much damage.
At this point in time, you're unstoppable and no one except for maybe Jax and Evelynn (When low on HP, and not really since the nerf) can kill you. All you need to remember is to COMMITT!

If you're not finished yet, you didnt help your team enough by killing enemies. In Super Late Game where everyone is practically level 18, your advantage closes and you need to use strategy more. By this time, most teams like to stick together and push the same lane. What I do to weaken them further is to hang behind them in the bushes. When one of them retreats is when you strike. Alternatively you can provide that extra kick in a group battle, but you have to be careful of getting stunned and snared etc etc. Try to kill the caster using method one first.

Ideally, you would get the middle lane and therefore gain levels faster and have the ability to gank both bottom and top lanes easily. Try for champion kills early game but dont over committ and get owned by the turrets/gankers. Also, please dont rage at gankers because ganking is obviously part of the game that makes it fun and unpredictable :) Turret diving is a massive no no until about level 12. You're way too squishy to take that much damage.
If you get a partner, the best ones are:
- Jax or Pantheon, for their ability to jump-stun the enemy so that you can catch up/make that final hit
- Lux, because she is snare/stun based and is really good at stopping enemies.
- Veigar, his pentagon stoppy ability has saved me and let me get kills so many times.
- Any other champions who are able to stun the enemy champion. You dont want a team mate who takes kills away from you so you should avoid partners like Fiddlesticks etc. This is because you can essentially take both enemies on earlier if you are fed.

GO AND KILL SOME NOOB NOCTURNE *** :D