hello, this is my first build i've made it's the build i recommend for a master yi if you want to make brutal kills and make difference between victory or defeat.

my master yi is all about damage he doesn't need much attack speed cause his skills allready give good speed.

the runes i chose;
i chose the armor penetration to do more damage the champions armor wont really help anymore,
beside that i have critical strike chance runes for more crit hits and more damage the infinity edge gives 250% crit damage so the sooner u have crit the more damage u will do.
the alacrity runes are for the little bit of speed we can really use to hit a bit faster the items doesn't give much attack speed only black cleaver gives 30% attack speed but thats all attack speed u need.
the quintesses is all about the armor penetration again just to ignore more armor and directly fully hit there health.

the masteries i chose is usefull with the skills and items we have it combined power will own everyone the heal spell with the masterie mender's faith is a good combined weapon when needed

the items we got is about attack damage a little bit penetration, attack speed, and crit the tiamat gives 50% splash damage and with the bloodthirster's combined with infinity edge will own every boss

the reason i putted heal and mana summoner spells is because we dont have alot of mana so we can recharge mana during battle to be able to finish off an champion.
we also have a healing spell i know we have a healing skill as master yi but during battle with bosses u cant really heal so thats why we also have the healing spell.