Corki
In version 12.7, Riot Games has had a relatively big buff for the Yordles race, which is the ability to reduce energy increased to 30%.
However, this change will become extremely unbalanced when you use the main Corki because this unit can continuously cast spells, causing huge and excessive damage when countered.
Sivir
If you remember, last Sunday, Teamfight Tactics Project Director – Riot Mortdog announced changes for version 12.7 and there was no nerf targeting Sivir.
Therefore, Riot Games had to urgently add a series of updates targeting Sivir to reduce the dominance of this unit.
Talon
Perhaps with the nerf to Talon’s damage and VIP effects in version 12.6, Riot was temporarily satisfied and did not nerf this unit at the announcement on Sunday.
Realizing this shortcoming, Riot decided to add the Talon nerf to the official version.
Martin 
Samuel 
Eliana