This guide will show you how you can easily farm gold with Master Yi early-mid game and defeat your enemies late game.
Before deciding to play Yi or not look at his Advantages & Disadvantages

Advantages:
-Insane late game damage
-Easy farming & harassment q-skill
-Destroys buildings in no time
-Outstanding movement speed
-Can stay on the lane for long time (w-skill)
-Let's say the truth - he's quite easy to play with

Disadvantages:
-Fragile like Paris Hilton's brain (low survivability - for ones who doesn't get the joke)
-Mana problems
-No escape mechanism (except ulti)
-No stun or slow
-Has 7 eyes

Greater Mark of Desolationx9 & Greater Quintessence of Desolationx3 let Master Yi harass even harder from the very beginning, getting through either low & high armor chars. And to be honest, the only problem, that a carry can face is tanks loaded with armor, that makes the damage output miserable. In order to counter these fat bastards ARP runes suit Yi perfectly.
x9 & - Master Yi is an end game champion. I prefer to max his crit damage, because late game he has enough attack speed and crit chance, so crit dmg will result in the best damage. I hope no need to explain why this Icon=Greater Seal of might] sucks hard

Masteries
Most of the masteries are quite obvious, but here is the explanation for ones that may cause some discussion:

1. Why Archmage's Savvy instead of Sorcery.
May guide for Yi bases on the fact, that you need money for items in order to become imba dps late game, therefor I prefer to increase dmg instead of reducing its CD, because anyway you can't just spam it all the time.
Someone may say, that it's good to have CD reduced for better chasing. The answer: if you can catch someone with Yi it's just not your champion, because his MS is incredible

2. Why 9 in Defensive, not in Utility.
Although I've written, that we aim at farming and Expanded Mind would add some mana and Awareness would increase exp gain, Yi is too squishy to be left without any defensive masteries. Moreover you will have to waste 1 point on super useless Good Hands - you aren't going to die much, right?;)

Summoner spells
1. - I think it is obvious
2. - the only thing that can stop Yi from killing is god dammed CCs. So this spell eliminates this problem
3. - quite good either you escape or chase

Here start the interesting part!
Over there I've shown the core items, that I take against all kinds of teams.

-You start with and x2. It will provide you will mana, so you can use your quite often, getting money for creeps & hitting your enemies avoiding being damaged by them.

-You stay at the lane until you get 1300-1400 gold - it will be enough to buy & . I'm starting to hear: "Wtf are you talking about, noob! for a carry - you must have a potato instead of brain". Believe me, when you buy this item you can stay on the lane making money with and healing with FOREVER. Your mana won't finish, because the lower it is, the faster you regenerate it.

-Now you make money really fast and you can get & . It's rather cheap and gives you everything you need for this stage of the game.

-You keep farming minions and get your precious . At this point killing becomes much easier (especially if you get the stacks). However, this item needs some skill, because if you die you lose your bonus dmg and life steal(LS). Anyway, it provides significant ammount of dmg and LS even if you lost your stacks.

-You kill everyone and get money for . AS, Crit% and MS - what else do you need to become godlike?

-And finally in most cases if they don't have more than 1 tank(off-tank) I take . Now you can go and destroy everything & everyone.

However 1 build can't be suitable against all teams, therefore I've decided to show you different sets of items for various types of teams.

1.They don't have a tank:

a) Insane build.

With the Ms from your ulti and x2 you don't need boots. This is more like a fun when your team is totally destroying the opponents.
b)Adequate

I decide to take even against low armor chars because Yi immediately decreases their armor by 45, which is enough to make them even more fragile. And in the end you can buy the second to get 85% crit.

2. They have 1 tank

or
You take against armor oriented tank and take icon=Madred's Bloodrazor size=32] against armor oriented one. Usually they stack both armor and health and in this case i would go for , because with lower armor your imba crits will devastate every tank.

3. They have 2 tanks(1tank+off-tank) or more.

combined with & will make any tank cry. If the game goes on you can replace your with .

I really do not recommend buying any kind of defensive items for Yi, because the more damage he deals the more he heals. You aren't going to make Yi a tank taking all the CC, right?

My skill sequence aims at maxing , because it makes great damage and allows Yi to harass even ranged champions. And I take 1 to have some emergency heal.

I feel comfortable either taking side or mid lane, but if you play Yi for the first time train a bit on the side lanes.
Side lanes:
Try to use your when there are 3 minions and enemy champions are close - it gives you 100% chance, that you will hit them, but remember DO NOT USE ON AN ENEMY CHAMPION, do it on the closes to you minion, so after the cast you come back, avoiding being hit. However, you can combine with and in this case you can jump on an enemy, but still be extremely accurate. I prefer playing early game in a safe way and attack an enemy only if it is 90% kill.
Mid lane:
Here it will be a bit harder, because you will face a ranged hero for sure, but the only difference is that you should use your more wisely - you should always hit 4 minions or 3 minions and a champion. You can push really well with only, you don't even need to hit minions. The hard moment is to go fast to the base and get your . After you get it you can easily keep pushing and healing.

I recommend ganging when you already have or even . Yeah, it will require some patience, but the result will be quite impressive.

Thanks for reading, hope you will enjoy playing Master Yi.
Any kind of advice is appreciated.