This build is not only risky, but some may see it as just plain dumb! But I'm a die-hard Master yi fan and I enjoyed using him as my prime leveling champion. In this build, that I have used in the past with success(often), Master Yi becomes a "Glass Cannon". This guide is absolutely not fool prove. If you find yourself reading this guide in hopes of becoming unstopable as Master Yi in every situation, then please do not continue.

However, this guide describes a very risky way to have fun as Master Yi. If you don't mind losing a match every now and then, and want to try Master Yi(if you havn't already given up on him), then I'm sure the rest of my guide is more of your taste.

Attack speed.
Armor Pen.
Critical strick chance.

The more of the above stats you can start with, the better chance you'll luck out and get first blood. Kills(and maybe just a bunch of assists) are essential for Master Yi. The full set of Runes this Guide suggests can make building early game so much easier for you.

Armor
Magic resist
ETC.(pretty much anything that is tanky)

The Master Yi that this guide will describe how to play is meant to be a little squishy. Sacrificing survivability for Damage. Runes that will help you take more hits from the enemy, at the cost of runes that will knock their socks off is not preffered by this Risk-taking Master Yi.

But remember to experiment with this build's runes. User-judgement is required.

Just to explain some of my thoughts in the masteries for this guide:

I don't suggest putting 3 points in Vapirism. 3% more Life steal isn't really all that important. Late/mid-game items like the Blood thirster supply enough life steal and around the time that Master Yi can pick up some easy HP off from minion waves/Jungle camps.

Get Swiftness. While it's not always easy to notice the difference early game, any bit of movement speed without the cost of early-blunt-damage is wise. You don't want your prey to get away easy, and when Master Yi is in trouble he runs away. (Hence the Nick-name "Master Flee")

Runic Affinity is useful later in the game. Master Yi, when he gets his bloodthrister(prefferbly mid-game, roughly level 13 or so) can take advantage of various minion camps for easy experience and quick money. Or just to steal life before hopping back into team fights(to slay the squishies). The bonus on the the Jungle buffs has often been very useful in 1v1 duels with the opposing jungle, or to keep you in game with extra mana and Cooldown reduction.

It's not easy to build all the items suggested in this build without lucking-out and getting fed. The items suggested are geared towards fast damage, with some reliable life-steal.

But isn't there roughly Two Opens slots?

Ofcourse. Writting a guide with one exact set of items that is best for all situations with absolutely no need to adjust is just plain impossible. But I can explain what might be useful to pick up in specific "what-If" Situations.

Another BloodThirster- This can be useful when playing agaisnt a team of Champions who build health, but not armor and lack several different stuns or snares. When master yi is free to strike without being disrupted, life steal comes in handy. This is futher justified, as characters that lack stuns or snares usually make up for it by packing on some serious damage. (Master yi is a great example of this. Sort of ironic)

Frozen Mallet- Master yi's ability to keep up with his enemies when they run away is usually key to getting kills. Frozen Mallet reduces some of the risk of being Risky Yi by offering some Health, and slows the enemies he attacks. The Attack damage on this item makes it very useful as well. This item is mostly useful against enemies that require mobility over Stuns/Snares. (Master Yi falls into this catagory as well, but when facing another Master YI, remember his ultimate removes slow effects.)

Trinity Force- A good portion of everything shouldn't be neglected. Master Yi can make use of the little bits of Ability power this item provides for more damage on his Alpha strike and more healing from his Meditate. The Sheen's Effect that you can get in this item is also some what handy for more burst damage.

Thornmail, Guardian Angel, Force of Nature, ETC- Items that include Magic resist and Armor is not heavily recomended for this Risky Yi. However, when playing against tanky characters that can lay down some serious damage (Like Volibear), some survivability is a must. This also goes for Enemies like Annie or Ryze. The usual builds for Annie and Ryze arn't to hard to chop down with Risky Yi's great damage, but they can hold you back with Stuns/snares. This makes their damage lethal and making these items more useful on Master Yi.

Favoring Wuju Style over Meditate or Alpha strike can be rewarding for early game damage. This is a must for the Risky Yi. Plus, all the suggested items supply Attack Damage and practically no ability power, making Meditate's heal and Alpha Strike's damage useless.

Upgrading Master Yi's High Lander and Wuju-style as soon as possible can increase the chance that this deadly combo will reward you with more gold for your build.

I suggest Exaust and Ignite.

Using these Summoner Spells for the early game kills can get you those expensive strong items earlier than your foe, awarding extra laning pressence. The Risky Yi is all about sacrificing safety for strength(with hopes that it pays off)

IF you find Master Yi to be to squishy for you, and simply weakening your opponent just isn't enough to help you, then switching Exaust out for something like Heal might be useful.

And if finishing the opponent off quickly isn't the problem, and people keep flashing away even when you exaust them, Ghost over Ignite might help you. While Master Yi's ultimate offers some great Movement speed on a short cooldown, it is still possible that some people could use this bonus speed early game (pre-level 6, where the most Risk of Risky Yi exists).

If You preffer to lane as this very Risky Yi, which is more than likely the best choice, then you might want to be prepared to Cooperate.

Laning with a Friend you know is easy, as you can discuss how you two will split the minions or any other benifets of the lane before you start the game.

But if you like to lane as Master Yi, then improvise. If you are laning with a Support Champion like Sona, then it's easy to assume that she would be fine with assists (but don't deliberately pop in and take kills.) But if you are laning with another high-damage dealing, Kill-dependent Champion (like Xin or some builds of Lee and wukong) Then Sharing the kills and minions would be wise.

Abuse Alpha-strike on minion waves when you have plenty of mana to spare. Alpha Strike can be very useful to not only damage many minions, but is also even more effective than simply basic attacking them. It is also easy to aim an Alpha strike to do some small harrasment on your opposing lane-members while farming.

Master Yi's passive damage enhancement from Wuju-style can also make farming very easy mid-game between ganking squishy enemies and dropping towers like flys to your fly-swatter.

Cons:

1. Very Squishy
2. Dependent on Support Characters or Beefy Characters
(Could use some more cons, Please feel free to post some in the Comments)

Pros:

1. Geared toward the fast and dangerous game-play a character like Master Yi provides
2. Fun, hardly gets old
(Like to Suggest a Pro for this build? What are Comments for? It'd be a dream come true if someone else could find something nice to say about my first build!)

Remember, Risky Yi is not very easy to win with. But by leading with Alpha Strike, popping wuju style and Highlander at the same time, and exausting your enemy as they flee in terror, it's easy to get fed. Mastering the Risky Yi could make the lanes of Summoner's rift your buffet line, it's all you can eat, but watch out for the crunchy tanks XO

(I didn't write this build for Dominion or 3v3. Sorry.)

-Techi =D