First of all, this is my first build posted here, may contain errors, please don't kill me...

So, all you Yi players that found this build guide may know the moment when you are losing and your team needs you. With this build, I tell you what to do if that happens.
For example:

Game starts. Machete, potions, blue. Whenever you have the gold for buy Lantern, go back to base and get back to the jungle. Sadly, most players enrage too much if the Jungler does not help or doesn't to it good. So they die like novices going under enemy turret trying to kill a Lux, for example. Well, you see that top guy is a n00b, you try to help, you die too. First of all, NEVER leave the jungle if it's only a LITTLE BIT possible to help. Stay in your jungle, get your build, and when on any of your lane a turret goes down, you know that the moment of Yi has arrived. You know that only you can save the battle, get nervous, what is completely normal, because you know it'S gonna be 1 vs 5, but I'll show you how to use it effectively.

Now, what is very important: You or you and a teammate can't shouldn't invade their blue
or red supposing a kill, because it's possible that there are 3 of them and only with the Q, a starter Yi doesn't make much damage...BUT...it's your decision.

(And sorry for my bad gramatical errors, I'm not english/american :|)

PROS:

-The passive is very useful for jungling and trying to kill somebody who's hp is same like
yours, just because you strike him 2 times in same time like normally one basic.
-The Q allows you to farm easily. And when an enemy (Example: Lux) makes the Ult, you can escape from it doing the Q on the champion. Working on Ult's like Ashe, Lux, Ezreal, Draven, Jinx; Kha'Zix's W, and many more.
-With your W you can or heal you after red/blue/ghost .
OR while they attack you waiting for the Q.
-The E is very useful to tanky champs, such like Malphite,
Rammus...you know.
-The Ult has got short cd, so you can use it for
Dragon or Baron.


CONS:

-You can troll yourself using the Q accidently on a minion
instead of a champ. Also, while you are (floating) with the Q, basic
and range attacks (Ziggs' Ult) can kill you.
-The E has no cons, at least, I don't think so...
-The W is useful, but if you think, you can heal the damage
of a receiving turret shot, you might be wrong (meaning in
starting game until level 10(unless you buy AP ._.)
-The Ult may be very powerful, but if you are slowed, you
won't catch the enemy the enemy (Teemo's mushrooms, Ashe's Q-shots etc...).
But, using it for escape is a great idea, due to the short cd.
Anyways, if they have a Nocturne, or somebody else who's ult
can kill you easily, you're down.


So, make sure what to do if an enemy comes to you, make sure if you can or not kill him.
Check his skills. If he has stun, you should kill him using the Ult, so after the stun, you
could reach him (unless the coward uses flash).