I'm just kidding go out there and show them what real fear and frustration means, also get fed the smart way. If you can get kills steal em this build needs a nice pile of gold but the end game is worth it.

use youmuus ghostblade together with your ult to decrease Q time and so on. Devourer Makes your E's passive act like a two shot trigger, one shot is normal the other has the passive plus a third strike from devourer. Crit is your real friend here so use it to gank bot lane as much as possible so you can get the gold to be able to kill another yi with full crit because you have more shots than he has and more cooldown on Q. Crit can also negate armor so tanks turn into squisies.

I dont really know what he's bad against I just recently found and made this build I mean if you have enough skill you can kill anything, even rito himself.

Thats where the guardian angle comes in so you can just sit and relax while that katarina is on a slither of health while you come back to life and murder her

Flash and smite easy as that, flash is to get to enemies and chilling smite makes them easier to reach.