WIth the introduction of LoL patch 12.13, not everything seemed okay at Riot's side. The devs thought that some of the buffed characters needed hotfixes. One of those hotfixes refer to Master Yi, Gwen and Sivir.

As Yi's autoattack and W improved, he got up to56% win rate. Here is what the devs said on the occasion:

In Master Yi’s case, we wanted to give him more optimizations to be more performant at higher levels of play and then move power from his more stat-checky elements after seeing how it landed, though we overshot. For Gwen and Sivir, the changelists were hard to predict and we’re following up accordingly after their strong launches 

Below you can find the changes on Master Yi after the first hotfix of the patch:

Base stats

  • Attack damage: 66 ⇒ 65
  • Attack damage growth: 3 ⇒ 2.5

Q: Alpha Strike

  • Cooldown: 18/17.5/17/16.5/16 seconds ⇒ 20/19.5/19/18.5/18 seconds

W: Meditate

  • Damage reduction: 60/62.5/65/67.5/70%, increased to 90% for the first 0.5 seconds ⇒ 45/47.5/50/52.5/55%, increased to 90% for the first 0.5 seconds

Sivir

Q: Boomerang Blade

  • Base damage: 25/40/55/70/85 ⇒ 15/30/45/60/75

W: Ricochet

  • Mana cost: 60 ⇒ 60/65/70/75/80
  • Cooldown: 10 seconds ⇒ 12 seconds.