6 Shadow has become a late innovation to set 2. Master Yi has received many buffs over time, and players are taking full advantage of his late game carry potential. By building Kindred attack damage based, you can win streak mid game and transfer items to Master Yi in the late game.
If you find a solid start of shadow units, or you are able to get lots of gold from creeps to eco up a lot of gold by 32. After rolling down, you can stabilize with Kindred as your carry as you level to 8 to find the rest of your units.
By level 6, if you find Annie or Yorick, you can fit in 3 shadow, 3 inferno, and 3 summoners. The summoner buff isn't necessary, though, so you can just use any forntline or upgraded unit you have.
Additional comp tips
Even though this build aims to hit 6 shadow, it's not advised to hold and upgrade all the shadow units you find like Veigar. Once you find your Master Yi, you can look for these units to complete your build.
In the meantime, use a build like Shadow Summoners to pivot into the late game. Units like Yorick and Annie are both great in the mid to late game.
Once you find Master Yi 2, you can sell your Kindred to transfer your items over, or build more items and keep your Kindred items. Make sure you have another Kindred to put in if you do replace her.
If you find Shadow Lux, you can drop the Senna and Veigar and fit in mystic or more frontline depending on your lobby.
Items like Locket and Zephyr are also crucial to this build as it allows your carries to breeze through enemy frontlines.