Welcome to my Master Yi guide. Please read, test and comment the guide before voting, thanks.

Master Yi is a fast champion that can kill someone in short period of time. He is one of the greatest carry,pusher and farmer ingame. Apart of great Damage Points, huge Criticals, great Attack Speed and fast Movement Speed he has a superb chasing mechanism as well as it can be used as superb escape mechanism.

Pros
+Great Damage
+Great Attack Speed
+Superb chaser
+Great escape mechanism
+Superb pusher, carry and farmer
+Good harraser

Cons
-Bad on early game
-Easy to harras (Melee)
-Low HP pool
-After using Ultimate on a gank that is not working out, he has no way of fleeing from battle.

Double Strike - Master Yi strikes twice every 7th attack.
Double Strike is a very good early game ability, thats make you hit 2X more. Enabling Wuju Style in a Double Strike you can hit 4X more! That is the best way to get the First Blood.


Alpha Strike - Master Yi leaps across the battlefield striking up to 4 enemies, dealing magic damage to each enemy with a chance to deal 400 bonus magic damage to minions.
Cooldown - 18/16/14/12/10 seconds
Cost - 80/90/100/110/120 Mana
Range - 600
Alpha Strike is a very good early game ability, that teleport you to your target striking 4 enemys in battlefield. He can be used to farm, killing minions very fast. You can't hit the same person multiple times, so catching 2 heroes alone wont mean you hit both of em 2 times. If you use Alpha Strike in your target and than enable Wuju Style and Double Strike, you can take out a great amount of oponent HP pool very fast (use this sequence to kill the enemy).


Meditate - Master Yi channels, restoring health over 5 seconds. While channeling, Master Yi gains armor and magic resistance.
Cooldown - 35 seconds
Cost - 70/85/100/115/130 Mana
Range - Self
Meditate can be a very good ability at early game, if you have a magic or a range enemy that draw your health without difficulty. With Meditate you can stay at your lane more time, getting more gold and exp.


Wuju Style - Passive: Increases physical damage. Active: Master Yi can activate this ability to double its effectiveness for 10 seconds, but this removes the passive bonus until Wuju Style becomes available again.
Cooldown - 25 seconds
Cost - 40 Mana
Range - Self
Wuju Style is a very good ability at early and late game, giving you damage all the time and if used its double your effectiveness.


Highlander - Increases Master Yi's movement speed and Attack Speed, becoming immune to all slowing effects. Additionally, killing a champion refreshes all of Master Yi's cooldowns, and scoring an assist reduce the cooldowns by half.
Cooldown - 75 seconds
Cost - 120/120/120 Mana
Range - Self
Highlander is the most important skill, used in all killing and runing combos. The best on it is that after killing an champion you can use this again and get an easy multi kill.

Good Summuner's Spells

Cleanse is a very good ability to kill and run, removing all control debuffs, silences and blinds from your champion.
I take Ghost because it allows you to move to the places where the action is happening in no time and it is great to use with your ultimate for a devasting movement speed.
Exhaust is a generally great spell, great for picking out champions in a teamfight making them unable to escape, to slow chasers or to blind enemy Attack Damage carries.
Some people prefer Flash over Ghost. Flash in to clean up a kill just out of Alpha Strike range, Flash out to escape a gank. Flash through the jungle to chase or escape.

Bad Summuner's Spells

You don't need Heal, you have Lifesteal.
Don't die...
Smite, mmmm this isn't a jungler build.
You don't need Teleport, if you want be fast use Ghost and Highlander.
Let tanks get Fortify.
You need mana, but don't waste a summuner spell for it.
Let supports get Rally.

Killing combos

1.(Early game) Alpha Strike + Wuju Style + Double Strike + Cleanse (Only if your enemy stun, slow, taunt, fear, snare, sleep, immobilize, silence or blind you) + Normal Attacks
2.(Late game) Alpha Strike + Wuju Style + Highlander + Double Strike + Cleanse (Only if your enemy stun, taunt, fear, snare, sleep, immobilize, silence or blind you) + Normal Attacks

Running combos

1.(Early game) Ghost + Cleanse (Only if your enemy stun, slow, taunt, fear, snare, sleep, immobilize you)
2.(Late game) Highlander + Ghost + Cleanse (Only if your enemy stun, taunt, fear, snare, sleep, immobilize you)

I take the Quintessence for Armor Penetration. This Armor Penetration is essential for a good early game.


I take all the others runes on Critical Damage. With 32% of Critical Damage added on 90% of Critical Chance from the items, its how you have 32% of more pure Damage!

Offense

3/3 Great early game mastery, increasing 2% Critical Strike chance.
3/3 Great mastery for Alpha Strike, increasing 0.6 Ability Power per lvl (10.8 at lvl 18).
4/4 Great mastery for Alpha Strike, Meditate and Wuju Style reducting 3% Abilities cooldown.
0/4 In lvl 18 with my item build and Master Yi ultimate you have 2.5 Attack Speed, you don't need more...
1/1 A very good mastery for Alpha Strike, increasing your Magic Penetration on 15%!
3/3 Good mastery counter tanks, giving you 6 Armor Penetration.
3/3 WOOT! More 3 Attack Damage.
3/3 Wow, more 10% Critical Damage (with Infinity Edge and Runes 292%)!
1/1 Very good mastery for Alpha Strike and Normal Attacks, increasing 5% Magic and Basic Damage.

Defense

3/3 Master Yi have only 52.5 Magic Resistance, with more 6 from mastery its 58.5.
1/3 Master Yi have only 82.9 Armor, with more 2 from mastery its 84.9.
4/4 Dodge is essential to the next mastery, than take it.
1/1 Very good mastery to run, increasing 10% Movement Speed if you Dodge.

You can replace a Phantom Dancer by a Sword of the Divine, if you have as enemy dodgers like Jax and Sivir.
You can buy a Sword of the Occult before you get a B. F. Sword, if you are starting to be feeded.
You can replace a The Bloodthirster by a Last Whisper, if you have to battle enemies with great defense.
You can replace a The Bloodthirster by a The Black Cleaver, if you have to battle enemies with great defense (But than you need to change Berserker's Greaves to Boots of Swiftness).
You can replace a The Bloodthirster by a Tiamat, if you need to kill many minions in no time.
You can replace a The Bloodthirster by a Hexdrinker, if you have as enemy feeded Mages.
You can replace a The Bloodthirster by a Thornmail, if you have enemies with a great Damage.
You can replace a The Bloodthirster by a Guardian Angel, if you are playing in a ranked game and don`t want to die.

Good Allies

Disablers (Stun, taunt, fear, snare, suppresed):
Alistar, Amumu, Ashe, Blitzcrank, Cassiopeia, Everlynn, Fiddlesticks, Galio, Lux, Malzahar, Morgana, Pantheon, Rammus, Ryze, Shen, Sion, Sona, Taric, Urgot, Veigar and Warwick.
Supporters:
Alistar, Janna, Kayle, Shen, Sona and Zilean.

Worst Enemies

Disablers (It is only suppresed, because the other disables can be stop by Cleanse):
Malzahar, Urgot and Warwick.
Range:
Anivia, Annie, Caitlyn, Ezreal, Gangplank, Heimerdinger, Janna, Karthus, Kennen, Kog'Maw, LeBlanc, Lux, Miss Fortune, Morgana and Ryze.

If you want to Jungle, I would advise you to follow MeesterCheeSeen Guide, the best Jungle Master Yi Guide ever!

The unique potential that my build has over the others is that it has a perfect combination of Attack Speed, Movement Speed, Critical Chance and Critical Damage, making Master Yi UNSTOPABLE!
17/6/8:
With this "bad" Score(12/6/8 before Penta Kill) I make a Penta Kill! It means that with this build completed you don't need be feeded to kill much enemies.

Healing Done: 4.311
I heal 4.311 life only with Meditate and Life Steal!

Largest Multi Kill: 5
Penta Kill!!!

Magic Damage Dealt: 36.257
This Magic Damage is only from Alpha Strike!

Physical Damage Dealt: 369.296
I deal 369.296 Physical Damage (with Normal Attaks)!