This is my Oneshot build for master yi.
Its my go to build for almost every game. It allows you to go full glass cannon and destroy enemy backlines in 2 or 3 basics. I would always go this build unless their team has 4 tanky champs and low burst damage. This build makes you able to face champs with high burst without having to worry about them killing you faster than you can kill them.

You should just farm youre dark harvest in the early game. If the enemy top lanner its an inmobile champ or you top lanner is easy to gank you can try ganking lvl 2 and get first blood. Try to avoid fighting the other jungler if posible. Remember to have a dark harvest stack if posible before any ganks. Getting lvl 6 its important.

After getting lvl 6 you can start trying to gank if posible. after an item o 2 you no longer need to be scared from the other jungler as you should problably be able to fight him if you have dark harvest. If you success in a gank pay attention to the wave and if theres a cannon minion stay for the stacks

After you have arround dark harvest stacks and 2 crit items you will probably 2 shots their carrys and you can easily reset from their deaths and deal tons of damage in teamfights.

Its very important to remember you should never initiate a team fight as you will instantly get cc`d and deleted. You should avoid focusing tanks with this build, always target the carrys.
You should let youre team o the other team start the fight as you try to flank their squishys, yi is a lot more efective if you fight with flash so keep it in mind.
If you get a kill in the team fight you will get a 70% restored cd on your abilyties and a 300ish extra damage from dark harvest so if you kill someone the smarter choice may be Qing another enemy rather than trying to escape. In most teamfights you either kill everyone or die.

+ Insane burst
+ Q+AA = kill
+ Earlier power spike
+ Allows you to go full glass cannon
- Worst against tanks
- less margin for error
- Dark harvest is weak early game
- Worst for doing objectives