Who am I? I am a nobody! I'm silver 5 on my main account and have been playing lots of Sword of the Divine Master Yi top lane recently. I went on Rumiah's stream (A diamond 1 adc) and told him that if he could get 25 kills with this build I would give him 5 brittish pounds. And guess what? He did lol. Late game evryone in the other team got thornmails and he should've changed to AP completely but didn't, but he won anyways so GG, that was a really fun stream to watch.
Link to the video of the stream: http://www.twitch.tv/rumiah/b/433857327 look at 5 hours and 30 minutes for the Yi game. Please do follow him! Oh well, enough introduction, let's go on to the guide.

PROS:
Can oneshot the enemy adc, top laner, jungler, mid, support at level 10. Oh yeah! He can one shot evryone.
YOU WILL LAUGH!
Can't get a bad game. If you get no kills just try to take as many cs as you can and go take kills botlane.
It's op.
Did I say it's op?

CONS:
Easily counterable late game(thornmail)
Squishy
Master Yi will get a rework soon:(

Just go plain 21/9/0 here for maximum AD. You could get 21/0/9 aswell and go for active item cooldown reduction. (Sword of the divine)
Runes, just go normal ad red quints, armor yellows and magic resist blues.
I have nothing else to add. ^^

RUSH SWORD OF THE DIVINE!
That's the most important item of the build. You don't even need boots early. Just get SOTD, get double strike and ulti + sword of the divine = around 800 damage in 1-2 seconds at level 9-11 which is the entire enemies health bar.
Just read the item notes for more details on items.

In late game, people tend to get bored of getting oneshotted and gets thornmail. Almost evry time I play more than 4 people take thornmails in late game. This is where you change to AP and troll their ***es OR just backdoor and win fast.

You have to split push and roam a LOT. Don't farm your lane, whatever you do, don't.
Split push much, they will come for you, but no champion in the game can 1v1 you so just ****ing split push and oneshot the pesky enemies trying to stop you.

Thanks for reading! I don't really feel adding more to this guide. When I look up guides I just check masteries, runes and items so I don't really feel like writing a wall of text is neccessary.

Cya! :)