Most people play Master Yi as a DPS champion, however some of them play him as AP. AP is perfectly viable, however i personally think this is the best build for Master yi. I will be focusing on a completely damage based master yi build this means that you will have NO survivability, however EVERYTHING will die at your feet in seconds. Including tanks. When you first look at the build you will think it is a fail. Try it once and you will love it i win 80% of my ranked games with this build.

This is probably the most tricky part. I go 100% offensive runes however most of them are completely useless only giving a little push early game. However, armor pen marks and quints are a 100% need. They will grant you a whopping 25 armor pen at level 1. Thats like all the armor of any champ.
Greater Mark of Desolation This is the must have rune. DO NOT go without it.
Greater Quintessence of Desolation Also a must have.
The seals and quints are your choice i go AD runes but for some that is too offensive if you prefer a slightly more defensive build go flat HP runes and flat mana regen glyphs for that early game lane sustainability.

My Masteries are at 25-0-5 getting as much damage as possible. Mainly going for the armor pen and the extra damage at low levels along with slight lifesteal and crit chance + damage. the crit chance will help late game as a little boost

This item build will normally remain unchanged. To start purchase a Long Sword and one health pot. Then proceed to bot lane with an ally preferably sona or janna because they have an extra AD boost. Master yi can mid if he wants to just lane is much better for him. farm minions and kill champions until you reach 922 gold or more then go back for a brutalizer and some boots if u have enough gold if not then just get health pots. This will leave you at 46 armor pen. full damage to any carry champion. not to mention you have around 130 atk dmg depending on your level. Keep farming and killing until you have enough for youmuus. 1350 gold. Then go back and get it. After this you have your bread and butter. keep youmuus on the 1 quickslot so you can easily access it and when u chase someone use 1RE and chase chase chase. you will have around 5 kills about now, so keep farming and save up for a vampiric scepter and then start the jungle path. If your jungler allows it take blue and red and start ganking madly. with exhaust and ghost no one can escape you. beware of stuns dont dive someone with a stun because you are extremely squishy.

AMAZING damage
Melts tanks
amazing chaser
instant tower pusher
amazing at escaping
KILLS A LOT

extremely squishy
cc annihilates him

For spells i always get exhaust and ghost.
GHOST? WHY NUB SUCH FAIL YOU HAVE ULT AND YOUMUU. when you get stunned for 2 seconds and there is an enemy tower nearby an extra 35% movement speed will clear a LOT of ground. Exhaust is for those other dps earlier game who are more fed than you or the really fast champions trying to get away. Other gr8 spells are surge for that extra atkspd early and flash for the escape and the ignite for those people who manage to escape with 1 hp.

I stopped early because i had to go, however this build requires you to anger your team a little. When a team fight initiates start out quite far away from the battle. (river to river) so that no one sees you then when you see stuns and other CC used dive in and start with the damage dealers most of them will die in about .5-1 second so after they are done go to the tanks which will take 2-3 seconds. Sometimes when your team is losing you will need to mass BD taking teleport will help that. In lane wait for a double strike then alpha strike the enemy and cast Wuju Style and attack him once to deal approximately 300 damage this is an amazing harass that can be used on level 2