As masteryi, Master Yi needs time to come online. He is really weak in the very early laning phase.

His level 6 power spike is quite potent. If he can go for short trades prior to hitting level 6, he can easily chase the enemy down and all-in them with his Ultimate r.

When Master Yi has completed his first component item, he will find it alot easier to secure CS and win auto-attack trades with the enemy laner.
 As masteryi, Master Yi needs time to come online. He is really weak in the early lancing phase. His level 6 power peak is quite powerful. If he can go for short trades before hitting level 6, he can easily pursue the enemy down and all-in with his Ultimate R. When Master Yi finished his first component element, he will find much easier to secure CS and win auto-attack trades with the enemy lantern.