Master Yi Build
Not Updated For Current Season
Last hit creeps and jungle while waiting for the next wave. Farming for gold and xp for the early item and level lead is very important to get fed. Harass with alpha strike, but don't get too aggressive and get killed since you are very squishy. Coordinate with your lane partner (who should have a stun) to get an early gank and 300g (also important!)
Your first trip back should be for the Berserker's Greaves. These are vital to getting that last hit and being able to gtfo after a harass. Next on your list is the Avarice Blade. You'll be holding onto this for a while for the extra gold income.
Start to initiate the opposing team grouping up by ganking a lane after grabbing Avarice. Gank when possible and keep an eye out for empty lanes. Empty lanes have goldmines of creep waves. Kill the wave and gtfo to jungle for more gold or back to support your team in a team fight. Grab a teammate and kill dragon at level 8 or 9 for the extra gold.
Your trips back for mid game are going to be for:
Cloak of Agility
Continue farming creeps and jungle as much as you can. You will need to support your team in fights much more, so don't stay in the jungle or empty lanes if they need you (and they will). If the opportunity arises where you are in an empty lane with a friendly creep wave very close to the tower, push it to the tower and burn your ghostblade/wuju for a quick tower kill and gtfo. If you know enemy champs are on their way and will reach you before it goes down, stick in until they are about to show up and then burn your highlander if you can finish off the tower and run away (make sure to use ghostblade before highlander as highlander gives the speed boost and slow immunity!). Taking down a tower only requires 2-3 surviving friendly creeps and 3-8 seconds depending how big your items have gotten.
Itemizing for late game:
Unfortunately it is time to say goodbye to the goldmine but hello to the ghostblade. After ghost, finish your phantom dancer. Next on the list is the recurve bow and then convert it into bloodrazor. If the game is long enough to allow you the gold, go ahead and upgrade your vamp into a bloodthirster or stark's.
Things to keep in mind:
-If you out level/out item the opposing team, abuse it to get fed.
-If you aren't surviving team fights, don't sweat it too much. Instead, back door some turrets. Usually at least one if not all of the opposing team will head your way, which is good. This opens up either a) less opponents on the field for a team fight or b) other empty lanes your team can push up for another tower kill.
-Never stand around. If you're waiting for a creep wave to come, go jungle for gold/xp. Don't worry about jungle buffs until level 7+ as they just take too much time to take out. Once you can get them with a good amount of speed, however, you should always be walking around with jungle buffs on you. They're just good.
-If you plan on going Stark's instead of Bloodthirster, upgrade your sceptre to the emblem of valour in the midgame. The extra lifesteal is worth it for such little cost and your teammates will thank you for the hp regen. Also consider your team's comp and if appropriate to help team fights push stark's up the priority list. The aura for team fights can make or break them if your comp is appropriate.
-If you're planning to play Yi just to laugh at a broken kdr, go play someone else. While he is capable of penta-killing the team given the right opportunity, that does not have to be his only job. Simply back door enough turrets and your team can push the rest. I have personally gone 1/6/8 and won due to 4 backdoored turrets. Destroyed turrets are as important if not more important than dead enemy champions. This also means if you do not have a high bounty to die (aka your kill spree reward) don't be afraid to die if it means you can destroy a turret. If you need two or three more seconds to destroy that turret and an enemy is there but can't kill you before it dies but will still kill you, kill it anyways and take the death. 300g in their pocket will not make up for the loss of a turret.
-Don't be afraid to blue pill often. Alpha striking should be done very often at creeps and in the jungle for speedy gold farming, but this makes it pretty mana intensive and you'll often find yourself unable to do anything except basic melee. While being Yi this is still very deadly, a little time between creep waves or to quickly get back after a jungle adventure will allow you to refill your mana pool (even if just 50-75%) and buy intermediate items, further enabling you to rape face.
-Alpha Strike, while mainly offensive, should not be only used for offensive purposes. Examples: Nunu is casting his ulti with a friend nearby, you shouldn't waste the mana and cooldown on your ulti to run out and won't survive if you stay in. Alpha strike his buddy and get out of range! Or, if you're really good at timing, alpha strike him. You are not a valid target for his ulti if you're in the middle of an alpha strike. Another example is you are being chased down after backdooring a turret, let's say by Anivia and two of her friends a little further behind. That ***** is going to throw a stun at you and/or slow you down with her aoe. Lucky for you there are a few creeps you left alive on the way back since the turret was low on hp and you didn't need friendly creep support. Alpha striking the creeps to both dodge her stun and put distance between the two of you is key. These are just some examples. Use your intelligence for the rest!
Exhaust- This is almost a must. It can save you in so many ways due to blind and slow as well as assist in chasing down an enemy. Don't burn it just for the armor reduction, but keep in mind the mastery spec does add it.
Ignite- I use this purely for early/mid game ganking.
Cleanse- One stun can kill you. One cleanse can save you.
Revive- Nothing is more annoying than a Yi that won't stay dead. This is a useful spell to have if you plan on backdooring turrets as it allows you to sacrifice yourself for the destruction of the turret.
Ghost- Can be useful for both ganking and running, but with highlander and ghostblade already in the build your run speed shouldn't be an issue.
Flash- mediocre for Yi at best, but can save you in the right situation or assist in getting in range to get an exhaust off during a chase.
Heal- Good for early game ganking and mid game team fights, but nigh-useless late game. Anyone squishy will die too quickly for it to be useful and anyone not squishy will barely notice you cast it.
Clarity- Yi does have alot of mana issues, but I don't think it's enough to qualify using this if that is the only reason. If your team will need it, go for it, but it's still going to gimp you.