In this build, I will try and explain my playstyles for each of the characters I use most often. The starting champion for them is Master Yi, The Wuju Bladesman. I play Master Yi as a DPS, as well as a tower pusher/backdoorer. He has extremely high burst early game, excels in tower pushing and ganking mid game, and can clean up a teamfight, and solo most champions in late game.

******New Notes from recent edit
Please leave a comment! I've played about 50 games with this build since I've posted last, and It's worked fantastically. My only complaint is that I wish I had included Sword of Occult! It has made many a game shorter than it would normally would because of the extreme amount of damage this build can dish out early. If you are interested in this component I will post it in items.

The runes I choose for this are sort of hybrid armor penetration and critical damage. I choose these because of the early game use (armor pen) and the ability for the crit damage to start hurting enemy champions before you get your first AD item (madreds bloodrazor/bloodthirst). I take flat armor seals because in a 1v1 against warwicks, and enemy DPS alike, it's likely that this small advantage is all your Yi will need to win with his <100 hp... if you are very lucky. The attack speed glyphs are really just convenient so i dont have to spend more IP on another kind of rune that is more expensive.

Runes not to take with Yi--

HP Quints: Yi is squishy early game. Giving him another 100 hp is not saving his life. It's simply making more wet toilet paper for an enemy bush gank to pierce. Dont check bushes as Yi. Dont allow yourself to be towerdived without casting meditate. (after CC)

Attack Damage: This and ability power runes are quite a joke if you check the math behind magic pen/ armor pen. They also give very useless amounts of damage, usually less than Amplifying Tome/ Long Sword. NOT WORTH THE IP.

I take offensive tree for the extra 5% on his high speed/ high damage burst early game, and throughout. For DPS, it's generally a good idea to take the offensive tree, simply because this bonus can mean a kill, or a death, in some cases. Utility tree could be considered, but cleanse has a relatively low spam use, even with the 10% reduction. The Cooldown help from ghost mastery is all I need. Also, if you were to need that cleanse more often, you are probably doing something Yi is NOT GOOD AT: Teamfights/ Fighting Disablers.

The other 9 points, I invest in XP gain, neutral monster buffs, (which are both very strong for this Yi as a permanent slow from lizard usually feeds Yi a kill, also he has relatively low mana pool, and though maxing Wuju with 3 levels of meditate by level 10 you dont tend to use mana often... there has been an occasion or two where I've been caught oom attacking an enemy, or simply killed enough champions with ULT cast that I couldn't regen fast enough to net a quadra or penta. Blue buff eliminates all the above problems I mentioned.

Every day I join games where Yi takes a DORAN'S RING, or worse... a DORAN'S BLADE as his starting item I cry inside. Good Yis everywhere should take the time to text box this poor soul and enlighten him of my build, and Yi's low level defenses. As I've said above, Yi with 100 more hp is just a more satisfying, if longer lasting, early game kill. Yi is quite useless and prone to gank before level 6.

I start with brawler's gloves and hp pot for several reasons.

1. With 475 gold you dont really have many good choices.
2. You're going to concentrate on last hitting for the first 10 minutes or so anyways..
3. Lifesteal Scepter for a first item is idiocy, you could buy 450g worth of HP pots
4. I play mucho Tryndmere, and it's his starting item. =D
5. It builds into Zeal, and allows for a slight chance for double strike crit. Yay!
6. The dagger that builds into Zeal is useless as you should not be attack spamming minions/champions anyways at this point.

The only other choice I've take on occasion is a Long Sword (+10 AD). It builds into Madred's Razor, and makes last hitting minions paired with Wuju Style extremely easy.

From your first item on is where the game really begins, so here things get a little hairy. You have basically 3 paths from the time you grab your gear, Wuju, and run to a sidelane.(this is not mid lane Yi, and a different item should be invested for such.)

1. You are last hitting well, and earn cash to buy straight to your berserker's greaves! Yay! no deaths and you might have an assist, or even a kill from a silly enemy champ who thought Yi was no threat early! Blue pill, buy them boots, rush that /d booty back to your lane and keep killing minions.

2. You are absorbing a lot of harassment, and have popped both your HP pots, leveled Meditate twice, and are mana starved/ low hp still! Or.. Karthus Ult is scary. Blue pill at 400g(ish) and buy boots of speed, and hp pots to absorb harassment a bit longer.

3. You have been killed before reaching your ult either because you dived with double strike lust, or were ganked/similar situation. Respawn. Cry to your teamates. Buy what gear you can, and head back down lane with a smarter head than last time.

Now I wont cover every possible outcome of your game playing my Yi build, but I will go to the extent to explain this build is very item dependent. You should be killing something at all times. After you buy your Zeal, or finish your first Phantom Dancer, feel free to either farm quickly to that lifesteal scepter, or start ganking a sidelane with aggressive enemies/ squishy ones.

After this you want to build to madred's bloodrazor, simply because the attackspeed is fantastic to allow Yi to hit 2 times a second, and become a hard hitting Wuju sword of doom. Madred's will further your ability to solo enemy DPS because of the extra armor it provides. It's also a great anti tank item, which yi tends to have trouble with. If you further have trouble with enemies buying the dreaded anti-Yi/Trynd (thornmail) I would suggest buying armor pen, but I will leave the secondary item choices at the bottom.

After you have completed madred's bloodrazor, and started farming for that B. F. Sword of bloodthirster facerape, it should be nearing the end of the laning phase. Take advantage of your ability to move fast, hit hard, and hit fast, and push turrets while the enemy team is engaging your own. You will be down a man in the teamfight, so be fast to warn your teamates that it is not your job to let the enemy team kill you. You will be stunned/taunted/snared and killed. That's what happens to Yi in teamfights, and there is no way to stop it... With this build. (CLEANSE REFERENCE FOR USE)

After your bloodthirster is complete, you have a decision to make. If you are doing quite well, and satisfied with the fact that this build works, you may take my route and buy towards Infinity Edge. This will make you hit much harder, and more importantly crit harder. If you are lacking in attackspeed and feel you could hit faster, That is very true! Build for a second set of Phantoms! you can even sell your boots to help buy it because the movespeed boost will make up for the loss. *IE, do not under any circumstance sell the boots if you dont have enough money to buy Phantom Dancers, down a pair of boots and attackspeed makes you vulnerable and slow. Yi should never be slow.

Now earlier I mentioned how anti Yi a certain item is. Thornmail. And for that reason, all DPS should fear a rammus/malphite who carries one. To counter this item I reccomend building a Black Cleaver, as it debuffs armor to an extent, and also carries a heavy punch and attack speed*. You could consider Last Whisper as a filler for this, as it also helps with heavy armor, but it is only if you cannot afford a black cleaver.


************New Notes concerning Sword of the Occult
Okay, so after about 35 games or so with this build I've had a roughly 2-1 win loss ratio, and I started to look at my past scores I'd achieved. Every one I've won, has been extremely well carried by an "OP Yi" in the words of my enemies. Either a late game quadra kill for the turret and nexus push, or an early game victory from surrender at Yi's ability to Wuju rape. Each game I've had 10-30 kills, and 5-15 assists with anywhere from 2-7 deaths. I started to think to myself, Hmm.. Maybe the stack items would make this better. I've always been hesitant to build stacks as there are items that are more reliable, and better in general, but the max stacked items are the only advantage. I started playing with Sword of Occult, immediately after buying madred's razor, and had a huge advantage. My win to loss ration went to 5-1, and most of my games were won at the 25 minute marker. If you begin to get confident with this build, and know your limits you can fill a SoO within the 20 minute marker, or finish around 15 stacks on it. The last 20 games or so with this build I've included SoO every game where the opposing team had fed me 3 or more kills early. My best game I even bought a Leviathan which i succeeded in stacking as well, and I found myself getting bored with how easy it was to win. Try the stacks out, but only if conditions permit, NEVER RELY ON THEM.

Aside from the notorious Doran's Ring and the unmentionable (this is where you gasp.) Doran's Blade Yis, there is a common misconception that Alpha Strike should the the first spell you take. QQ aside, Yi functions much better with his other two spells maxed first for a long list of reasons.

Level 9 Alpha Strike simply deals a 300dmg nuke, yaaay, but no cigar. The amount you can deal with level 9 Wuju Style is the equivalent of an Infinity Edge AD, and with Yi's Inate (double strike) and Ultimate (Highlander) You can turn Wuju into an eerily chinese sounding death-machine. When I say level 9, I'm assuming you all know that at level 9, every LoL champion can have already maxed one of his skills.

Also the reason why I dont grab alpha till mid game is because for farming, it's really a random chance. I dont like to rely on random chance. (how funny, this is a crit build more or less..) Last hitting with Wuju is very very strong, and it pays out bigger gold than all the AP Yi Alpha Strike can cast.. every 12 seconds or so. ;D

The combination of Wuju and Meditate early is very strong for laning, as it allows you to bait inexperienced towerdivers into trying to kill you at >300hp. It allows you to deal a high burst, and unrivaled AD early game, as well as heal large amounts of damage.

From my experience this skill sequence is unrivaled in this particular Yi build.

I take Ghost and Cleanse for simple reasons. What is more irritating than Yi running away with 20 hp from an exhaust/slow of some kind after punching a turret to death? A Ghosted Yi, Running like an ethiopian kid on meth, that just cleansed out of amumu/malzahar/warwick/sion/swain stuns, after killing two inhibitors and a nexus turret.

Explains itself.

***************Recently added notes
There are some optionals you can take, and I will tell you when and why to use them.

Exhaust: Overall useful spell, since last patch it has made it the perfect anti-carry, shredding an enemies ability to fight back, and move. If you get tired of being blown away, or losing teamfights, feel free to take this. However the set back is it only allows you to CC one target, and you tend to be kind of weak teamfighting anyways.

Ignite: Obvious use is the true damage DOT, but the more useful one is the heal debuff. Very usefull for ruining a Mundo ultimate and killing him, as well as taric, fiddlesticks, and other major healers. Again, other spells are more useful, which is why i stick with Ghost and Cleanse.

Ressurect: Now i know this is considered another noob spell along with clarity and heal, but consider this, you died late game, and your team needs that person to wake up from the grave and finish a teamfight for a quadra kill, or maybe finish the turrets and nexus off alone. This is the spell for those Yis that have trouble finishing late games. Also allows you to tower dive extremely early if that's your kind of kill, but personally the cooldown is too long for use, and you shouldn't be dead too often anyways.

Teleport: Useless, in the time it takes you to get there you will not kill an enemy unless they are mentally ill, which case it's not very satisfying.

Heal: Useless, lifesteal and Hp pots are much more effective, and dont have a long cooldown. Tier 1 spell.

Clarity: Useful for Swain, Taric, and Karthus. I wouldn't consider it for anybody else, there are two infinite mana monsters that respawn on the map. there should never be a need to spam enough spells to use this, or think you are hungry enough to need it. Moving on.

Flash: can take instead of ghost, but has a longer cooldown, and for this build with yi's anti slow Ult, it's generally better to be able to run like crazy rather than blink like a cyclops. Really a matter of taste here.

Yi is made to be a farmer, assassin, carry, and DPS. With this build, he does his jobs very well, and even exceeds at bringing down turrets quickly, and backdooring. He is PentaKill worthy of cleaning up teamfights, of which I've made 4 Pentakills in all of my games, and an uncountable amount of doubles and triples and quadras.

****Edit
I've added a sword of the occult item build on the second Yi, as well as a armor penetration Yi that works as a very good anti jungler, and support dps. Both are effective if the typical DPS Yi is not working. I aim to make a hybrid and ap yi build in the near future, as well as a tank Yi for giggles. I also intend to include icons in this build.

Important Strengths and Weaknesses
Yi is very strong at pounding weak champions early with this build.
Tower destruction before 10 minutes.
last hits 100+ minions before 15 minutes.
Beats wanna-be DPS every day.
First blood surprises enemies every time.
Taunts on an enemy nexus from Yi are infuriating.
Killing Lifesteal Yi/ Warwick is satisfying.

Weak in teamfights.
With cleanse on cooldown you will find yourself spamming keyboard keys futile from stuns and taunts.
Teamates tend to complain highly of you not helping them when they die in stupid positions. (when is that different..I'm not taric.)
Playing Yi poorly is very unrewarding.
Thornmails suck.
If your Ultimate is on cooldown you are playing in a position you do not want to be in.