My friend asked me to make a build thingie for yi since apparenlty hes bad as him xD. So Yi's pretty much jsut a right click Character. I usally put all my points in Q and E then R whenever i get the chance. Not putting any in W till late game were is till barly use it.

Note: When healing at the spawn use W to heal faster.
Note: Item build last 3 are your choice depending on game.

First buy a Dagger and one health potion. farm till you have enough to buy Berserker's Greaves.
Next buy Last Whisperer, followed by The Black Cleaver then Stark's Favor.After that ill buy a Phantom Daancer.Now you have to judge the game if your getting some deaths ill but Thornmail and if by Magic characters buy Force Of Nature.If your not getting killed alot buy another Phantom Dancer. By here the game should be decided on whos gunna win.

Ghost to Catch people then Exaust ussally ends it there.

If they dont ahve alot of HP open with Q then E or R one after the other it doesnt matter. if being chase run to bushs or a tower and use W and surprise them since they wont expect you to have most of your HP back. so Q E/R = Death

Yi normmaly doesnt work as a team and jsut Ganks people who are alone or running. But he can jump in during team fights and clean up.

Low defense not good at fighting groups expeccialy Tanks such as rammus with a thormail = getting owned.

Any rune with Attack Speed, CD's, and Crit will be msot important. if you have extra soaces go with HP or Hp regn.