Master Yi is very hit dependent, if you don't hit and get hit a lot, you are dead. It's good if you focus the enemy team's damage dealers first, as in focus the squishy ones. You will kill them easily and can Q again instantly. Don't be afraid to use your ultimate, because the CD will be done by the time you B and etc.
During laning phase, your number one priority is farming properly and last hitting. Don't lose any CS (note: This does not mean get hit for free, while trying to CS. If you let enemy harrass or poke you for free, you will lose the lane automatically and lose the CS as well, so if you have to, let go of some minions) and don't go in balls deep on the enemy if they are around their minions, because early game, the minions do a lot of damage, think of it as a mini ignite. However, if you want to harrass, you can sometimes wait till you get double strike, and Q at them then use E which will in turn proc double strike, E true damage and Thunderlords and this deal tons of damage early levels. You can back off straight away after this, so they can't attack you. Pushing is never a good idea, because if you push, the enemy will turret hug, and you will most likely get ganked, and let's say you have a chance to kill the enemy laner, but you can't since he is turret hugging. But if you play safe and passive, he will push you, and you can then suddenly surprise him and kill him, and all he can do is run towards his turret but since it's far, he will die before that. Not only this, but your jungler can gank you easier.
I myself use this build a lot and have been using it since 2009. You can kill easily with this build...But beware of Thornmail and CC. Try to not get caught in CC or else you are dead. However, if the enemy team has a lot of CC, try to build Mercurial Scimitar or/and Guardian Angel to get out of sticky situations. Getting pentakills is easy, even if you're solo, all you need is to be fed and for them to make a mistake to fight you without tanks or any damage, you can kill all 5 easily if you know who to focus!

NOTE; Infinity Edge makes you deal more than 800 damage, but it also makes you lose more health if the enemy has Thornmail! My max was 1.9k damage back when Yi wasn't reworked on.

(This is my first build guide, updated and edited.)

+ Is strong throughout the whole game
+ Can one shot enemy squishies and forces them to buy sustain items which in return will decrease their DMG output and most likely the sustain items won't help
+ Will end games quick and can carry easily
+ Farming, pushing and killing enemies is easy
+ Has presence and will most likely get focused
+ Takes down turrets without ultimate with just 1-2 waves of minions, if left alone
+ Can split push or team fight whichever style you prefer

- Easy to counter
- Is weak against Thornmail, CC and burst if not built correctly
- If used wrong, can be useless and weak, in other words if played wrong, will be useless and won't show it's true potential
- Depends on enemy mistakes / Team mate sacrifices (Not always)
- If gets camped, countered and falls behind, takes some time to get back into the game, but once he does, he will still be strong.

Flash
Good for escapes and catching up
With Flash, you can get over walls if needed, escape easily and close gaps quickly to get in range so you can finish off a target. Is great since you have Alpha Strike
Ignite
Gives you that extra true damage early game
Yi needs extra damage early game to finish off enemies quickly and get an early lead and snowball
Ghost
Speeds up character for a short duration of time
I myself don't really use this, but it's a great pick nonetheless. It stacks up greatly with Youmuu's Ghostblade and Highlander
Teleport
Teleports you to an ally turret or minion
This is good, if you need to get to lane quickly for more experience or CS. Not only that, but it's good for teleport ganks and dragon fights early to mid game. However I don't pick it on Yi


I explained runes on the "RUNE NOTES" but I will explain it here as well.
Okay so, the reason these runes are super good is because, they give both attack speed, as well as attack damage equally. Early game, this is a huge advantage, because it won't feel like it's too much of one thing, and too little of another, in fact it will feel perfect. The damage output will scale perfectly with your item build so there will never be a time you will feel like you lack attack speed or attack damage, unless you fall super behind.

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• Double Strike This is Master Yi's passive. Every fourth attack will be a double strike and the second strike will deal half of your attack damage. It cannot critically strike, however this passive is really strong considering we are going to build attack speed.
  
• Alpha Strike Master Yi leaps to 4 enemies, landing to the targeted enemy unless they are dead. If they are dead, he will land where he started from. Good Master Yi players don't start with Q usually, because you can use Q to dodge CC and other attacks that can be fatal such as a turret attack and aggro. However, if you need to close a gap, you may as well use this. The CD of this will reset almost always, if you kill someone, or attack someone enough.
  
• Meditate Master Yi starts meditating, and heals up for a certain amount of health and takes less damage. This skill, isn't exactly like other Master Yi's abilities, it's not offensive, however you can use it offensively, by canceling animations using W. It's a great sustain ability. Can be used to tank turret damage and other people's damage. It can also be used to survive long enough for your Q/E CD to reset.
• Wuju Style Master Yi gains true damage for a short duration of time. This is an underrated ability in my opinion. The fact that it gives Master Yi bonus AD as well as true damage when activated, makes Master Yi so strong. It's like the ability is made to shred through tanks and melt squishies.
  
• Highlander Once activated, increases Master Yi's movement speed and attack damage a lot and Master Yi can't get slowed down, however Master Yi can get CC'd. This is an ability that has low cooldown and is perfect for someone like Yi.

Maxing E first is like I said the best option, against tanks as well as squishies. Simply because of the damage output it gives. The true damage scales greatly with your Youmuu's and your E also gives bonus AD. Oh and getting W early is good for lane sustain and harrassing. You can also use animation cancel with W and do two fast auto attacks in a row. AA>W>AA really fast.

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Honestly, I have no words for this item. After Yi rework, this item is like it was made for Yi. It gives so much early attack damage, penetration and the active is great. With the build we're going, this item is the main item that Yi would be nothing without. It gives both attack speed, attack damage and penetration as well as movement speed.

Boots are self-explanatory. Yi needs these ASAP, because movement speed is great and it scales with Yi's ultimate. You can stick to enemies like a tick and do damage nonstop which is good. That's why it's a necessity. With Youmuu's Ghostblade and Highlander these are great.

I used to be against Statikk Shiv on Yi before, however now I am on Statikk Shiv side. The item is pretty darn good becaues the charge can critically strike and it's magic damage plus on top of this it gives both attack speed and movement speed as well as critical strike chance. This means Alpha Strike can proc Statikk Shiv charge and do critical damage. Which is a huge amount of damage suddenly.

Infinity Edge has always been one of my favourite items, even after it got changed. This is purely because it gives flat AD as well as critical chance and critical damage increase which all, Yi needs.

This is my choice of a tanky item against AD. It's because the item gives movement speed once it's charged, and then that first attack deals bonus damage and slows the enemy. Not only that, but it gives a lot of health and armor so you will have sustain.

I've always preferred Spirit Visage over Banshee's Veil because of the way they are built. Both are great items, but I just prefer this more because IF you do get lifesteal, it becomes better. You honestly don't need more MR or health after this.

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This is a good item, for when you need extra damage and armor penetration, but also need magic resist. It also gives a shield before you die every 90 seconds, which is great.

In my opinion, this item is better than Bloodthirster because this deals percentage health damage which is why it's good against tanks. It can shred them and do huge amount of damage, meanwhile giving you lifesteal and to top it all off, it has an active that slows the enemy dealing damage and giving you a bit of their movement speed and heals you.

This item is great for when they have a lot of CC that you can't dodge. For example an Annie. The item gives magic resist and AD as well so it's not a waste to buy. When activated, clears out all CC and gives you a short movement speed boost.

If the enemy team is heavily armored, for example squishies have Guardian Angel, Iceborn Gauntlet or Zhonya's Hourglass you should get this item then. This will help you deal the damage you're supposed to and will render their armours useless.

Not really my favourite pick, however it is a viable pick. It's good when the enemy has a lot of burst, and they can burst you easily. It will help you get focused less, and it will revive you after you get bursted down giving you more survivality.

Play Video
This build does almost as much damage as back then.

So that was about it, this is it for my "Fourth Generation" build on Mobafire. I put a lot of work and time on this build, and was lazy at times, so if you find any errors or mistakes, do let me know. Leave a feedback so I know where to improve and what to do next. If you have any questions, ask away and if you don't understand something, I can explain it to you. I personally don't want to release this build, because it can lead to Master Yi getting a nerf, or the items getting a nerf which will make Master Yi USELESS. Right now, with this build he is a "Secret" God Tier champion in Top/Mid. This build doesn't work on Jungle, however if you tweak it a bit, it might work although a bit slower build path. Test out the build against bots, practice Yi in Normal games and once you learn the basics, you're good to go.

Yours truly, Nik