This is my first attempt at publishing a build so I would enjoy any feedback on a way to improve the presentation. I will be finishing it but wanted to get at least this part out.

As far as I am concerned Master Yi is one of the most powerful champions in the game. Now with that said it depends on many things. This build is based on attack speed and crit damage. I will try to cover the reasons for my selections in items and ability. this is all based off my in game experience and requires a decent amount of farming and smart play. You can expect to see 950-1000 crits 95% of the time when built and is so fast that played smartly quarda and penta is something you will hear a lot. 1v1 and even 1v2 their is not any champions that i have come across that can withstand this build.

Keeper of the ancient art of Wuju, Master Yi is a mystical warrior from the isle of Ionia. He descended from one of the few tribes dedicated to the preservation of Wuju, a martial art founded with the principles of absolute spiritual awareness of one's self and one's enemy. When the armies of Noxus invaded Ionia, Master Yi joined in the Ionian defense to fight the craven enemy, bringing his village honor through his unparalleled mastery of the blade. The ensuing battles ravaged the land, but no conflict inflicted as much horror as the day the armies of Noxus closed in on Yi's village. Left undefended, the village became the unfortunate test subject of the latest invention by an up-and-coming chemist, now known as Singed. The remains of the village that Master Yi returned to were so horrific that it remains a festering scar on Ionian history. To this day, no Ionian will ever publicly speak of what occurred.

After the Noxian invasion was contained, Master Yi fell into a deep isolation. For years, he trained morning to night, speaking to no one and refusing offers of consolation by fellow Ionians. The only thing stopping him from madly charging into Noxus battle lines headfirst was his pledge to keep the Wuju style alive. Even though he seethed with impatience, his rage became a tool for sharpening his practice of Wuju, developing stronger and deadlier skills for his eventual vengeance. The only thing that roused him was news of the League's formation, and Noxus's subsequent enrollment in the League. Master Yi now brings his mastery of the blade to the League of Legends with unflinching purpose: to avenge his kinfolk and end the predations of the Noxus once and for all.

"The art of Wuju lives on in Master Yi, and is plunged through the hearts of his foes."

Pros
Great pusher/tower/farmer destroyer
Pretty easy to learn overall
Great escape/chase mechanism
Ult resets/halves when you get a kill/assist

Cons
Vulnerable to disables like blind, stun,suppress...
Low HP poll until you get Banshee's Veil (or other HP item)

Greater Mark of Desolation x9

This is a must to get as much to the target as you can and is a huge help in the early game.

Greater Seal of Furor x9

The crit damage is a core part of this build and the higher it is the better since you will have about 95% crit rate.

Glyph of Warding x9

Mainly i take these to knock the edge off the ap champs that can hurt pretty fast especially early game.

Greater Quintessence of Desolation x1

Adding this to your marks means early game you do mostly true damage.

Greater Quintessence of Furor x2

Again this build is based on speed and crit damage so the more the better.