Master Yi needs time to scale and will be looking to farm as much as possible to come online. Without his Ultimate R, he is rather weak, so he will be looking to hit level 6 as quickly as possible.
Go in Master Yi’s jungle to steal away his camps if you see him on one side of the map. This will delay his power spikes, and also reduce his gold income.
Master Yi can take objectives like the Dragon or Rift Herald alone in the early game. Make sure you keep those objectives warded so you can see him before he secures them for his team.
Disengage is Master Yi’s worse nightmare. As soon as he activates his Ultimate R and runs towards your team, disengage so he cannot take over the fight.
When low, make sure you back away even if Master Yi isn’t there. If he picks up free and easy kills, he will snowball heavy and take over the next team fight.
Try and wait for Master Yi to use his Q before locking him down with CC. As he can use his Q to dodge skill shots and CC if timed correctly, it’s best to wait for him to use this ability before trying to kill him.
Master Yi will get strong and stronger with the more kills he’s given. Avoid giving kills to him in the early game.
Once Master Yi hits level 6, he will start ganking as his Ultimate R offers him tons of added kill pressure.
Master Yi is very strong in the late game. Try to reduce his income to make it harder for him to snowball and take over the game.