Yi has a great potential to do a great deal of damage with the right build. This build will help you do that.

This is bulid is focused on AD and Life Steal.
Many people believe Master Yi is better with Attack Speed. However, Yi has the ultmate skill that gives him upto 80% Attack Speed. With just a few Attack Speed items, Yi can reach the Maximum Attack Speed easily, therefore, too much Attack Speed on Master Yi gets wasted. This makes Master Yi a better champion with a high Attack Damage, not with a high Attack Speed.

Build

Pros
-Crazy burst damage
-Can stay in lane long

Cons
-Low Survivality against Heavy Damage Team or AOE Team.
-Weak Against CC Team.

24/6/0

Some people might ask why 2 points on offensive mastery(more damage on minions).
That is because it helps Yi get more minions kills early game. It is not easy to measure the last hit, and sometimes you just dont get some minion kills by 1~4 health. This mastery will let you get minion kills easier and give you more gold early game.

Mark Runes - This build has low critical chance until you get Infinity Edge.
With the masteries, this runes will give approximately a 10% crit chance, which will help you get burst damage.

Seal Runes - Flat Mana Regeneration runes enables Yi to stay longer in lane as Yi can cast Meditate more often. This also helps him use other skills more frequently.

Glyph Runes - Magic Resistance per level gives him higher survivality as this build doesn't give Yi any Armor or Magic Resistance. Having about 20 Magic Resistance at level 18 reduces incoming AP damages quite alot. (~8%).

Flath Health Quintessence helps him in many ways early game.

Movement increase Quintessence helps him chase enemy champions/run away from enemy champions. Even if it's only a 1.5% movement increase, this helps him chase down enemy champions and hit the target more constantly (The increased movement speed makes up for the delay of Yi's Auto Attack). Also this helps him get away from enemy champions sometimes.

Exhuast : This lets Yi take down any champion in 1 vs 1 fight, and lower damage output of an enemy ad carry in team fights. You really want this as Yi.

Ignite : This will do Additional damage to enemy champion and help Yi take down the target even easier. Also incredibly good as finishing skill.


Do Not Use

Ghost - You have Highlander. Also this doesn't help you in fights.
Flash - Again, you have Highlander. You can also Alpha Strike to get to the enemy champion.

Doran's Ring: is the best item to start with because it gives Yi additional AP damage on his Alpha Strike and additional health regeneration on Meditate. Also it's mana regeneration helps Yi to stay in lane very long.

Boots: Boots

Stark's Fervor: has lifesteal/attack speed/health regen/armor reduction. Yi's Wuju Style makes this the perfect first item to grab. It will have about a 100 attack damage with increased attack speed, life steal. This makes Yi incredibly solid in lane.

Blood Thirster: now we have attack speed with Stark's Fervor, time to become a real badass with powerful damage. Blood Thirster will give Yi an incredible damage with more Life Steal. Now Yi deals crazy damage in fights. He also can literally farm/jungle forever very fast.

The Black Cleaver: maeks Yi wields even stronger sword. Yi will penetrate through target's armor faster and stronger. At this point, Yi become extremely strong with his skills and put down squishy champions in just a few seconds. He can also take down tanks easier since he now has 65 armor reduction from Stark's fervor and black cleaver.

Frozen Mallet: By the time you get this, the enemy champions might have crazy damage. Frozen Mallet gives Yi higher survavility. This also lets Yi not lose any enemy champion who tries to get away from him. So if Yi engages in 1 vs 1 fight at this point, the enemy champion can neither run away nor beat him.

Infinity Edge: additionaly 80 Attack damage and 25% Crit Chance make Yi ultra strong. You will get see yi take down one squishy champion within 2 second with his passive.

Phantom Dancer: If the game lasts longer than you think, sell your boots and get Phantom Dancer: You now have 65% Crit chance with almost maximum attack speed. Your movement speed will still be fast enough with your movement speed rune and Highlander.

Alpha Strike is very good to gank/harass enemy champions and farm minions. Max this out after you learn each skill by one level.

Meditate lets Yi stay in lane longer early game. Since you will get Life steal items later, one point is enough until he maxes out other skills.

Wuju Style makes Yi incredibly strong all around the game. However the increment of damage is low after the first level, so I'd recommend to max out Alpha Strike after giving one point on Wuju Style.

Highlander optimizes the damage of Yi with high Attack Damage.