Master Yi - is a melee DPS champion with massive damage capabilities. This build maximizes his DPS and will insure the best 1 v 1 w/o Thornmail.

Master because of his damage is one of the most feared champions and will be targeted by most enemies and taken out very early in team fights. Your goal as Master Yi is to cause as much damage to the enemy team as you can. Wait for the team fight to start and after about 2 or 3 sec run in and target the casters and carries first. Then move on to whoever is left.

Ghost- Great spell to chase down enemies and great when used with Highlander.
Cleanse-Great for eliminating disables and summoner spells like exhaust/ignite

Cleanse is swappable with Exhaust.

Pros-
Massive Damage
High Speed
Great 1 v 1

Cons-
Can become useless because of exhaust/ignite
The enemy team will target you first

Yi can be great at farming when you spec int o Wuju Style early. Alpha strike is also great because it hits multiple targets and has a chance to do massive damage.

If you choose to jungle with Master Yi pick up a Wriggles lantern as a first item. then swap it out later for a Bloodthirster.

Skill order for Jungle:
QWQEEREEEQRQQWWRWW

-Obtaining Red buff can ensure that you get kills easier by slowing the enemies.
-Once you are level 6 make it obvious that you are recalling to the enemy team. Once you buy your items, gank middle.
-Use Alpha strike in the laning phase to hurt champions for far away. Be sure to select minions with this because when you leave alpha strike you are on the target that you selected.
-In team fights use alpha strike not for damage but to get to your target fast and auto-attack them.
-Use Highlander in any situation you know you can get a kill in. When you kill an enemy champion all his abilities refresh when highlander is active.
-Use meditate when you are positive you will be hit by a ability as it increases your armor and magic resist immensely (i.e. Karthus Ultimate).
-When there is a fed enemy caster(i.e. Karthus or Veigar) use the meditate abitiy to block some damage or even go as far as buying a hexdrinker for the passive ability

Thornmail

+100 Armor UNIQUE Passive: On being hit by standard attacks, returns 30% of damage taken as magic damage.

-Thornmail is a great counter to yi.
-If a tank acquires a Thornmail and other health/armor items, Master Yi can kill himself on thornmail alone.

Possible Counters-

-Building lots of lifesteal.
-Building Madreds Bloodrazor
-Switching the build to all AP.(i wouldn't recommend this)
-Avoid the champs with this item.
-Building Magic resist (i wouldn't recommend this either)

Frozen Mallet

+700 Health +20 Attack Damage UNIQUE Passive: Your attacks reduce your target's Movement Speed by 40% for 2.5 seconds (30% for ranged attacks).

Hexdrinker

+35 Attack Damage +30 Magic Resistance UNIQUE Passive: If you would take Magic Damage which would leave you at less than 30% of your Maximum Health, you first gain a shield which absorbs 300 Magic Damage for 4 seconds. 60 second cooldown

The Black Cleaver

+55 Attack Damage +30% Attack Speed UNIQUE Passive: Physical attacks reduce your target's Armor by 15 for 5 seconds (maximum 3 stacks).

Wriggle's Lantern (Jungle Yi only)

+23 Damage +30 Armor +14% Lifesteal UNIQUE Passive: 20% chance on attack to deal 500 damage to a minion. UNIQUE Active: Places an invisible ward with 1100 range sight that lasts for 3 minutes. 3 minute cooldown.

Youmuu's Ghostblade

+30 Attack Damage +15% Critical Chance UNIQUE Passive: +20 Armor Penetration 15% Cooldown Reduction UNIQUE Active: You gain +20% movespeed and +50% attack speed for 4 seconds. Attacking enemy units with melee attacks increases the duration by 2 to a maximum of 8 seconds. 60 second cooldown.

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.'' -- Soraka, the Starchild