This champ is the fucking worst. Now some of you would say "he's not busted, just cc him or build armor/health". Well guess what happened. I was playing galio with and i had built a thornmail, ROA, tabis, and zhonyas. Yi just flashed on me and i died in 3 aas. I insta press w for taunt, but stormrazer proc, half my health gone. two more aa in less than a sec and im grey screen. Great champion, so much counterplay.
He was likely insanely fed then. If you don't feed him early he's not much of a problem, especially if you have big tanks to protect your squishies since he dies in seconds.
the only 3 ways to stop him is tons of hard cc (
and 
are beauty for that for example), a lot of burst, and a whole SHIT TON of HP. His E does flat true damage, so the more HP you have the slightly better of a chance you have survivng. as dumb as yi is, that's litterally the only way you can counter him. tons of stuns/roots,
disarm helps tons cuz it stops him from AAing entirely, 
cuz cant hit what you cant see(love taking akali into AA based enemies ESPCIALLY 
), there's
too. and
is prob your best survival option. if you want a tank, then 
is a good way to fight his E- Wuju style, cuz not only does can he build , he can also build 
if he wanted to, and his R allows him to recover a lot of HP rapidly. just my opinions anyways. i hate yi as is. i call him the insta win champ. oh and 
(challenging smite reduces damage taken by 20%, dunno if it applies for true damage tho) and 
(reduce damage dealt by 40%, tho it doesnt stop true damage :( )
(reduce his healing(grevious wounds>40% less healing) from W and whatever healing items he builds) helps too
