Improved Critical
From Neversummer 4 Wiki
Type of Feat: General
Prerequisite: Proficiency with the chosen weapon, BAB +8
Required for: Overwhelming Critical
Specifics: Combat ability doubles the critical threat range with a given weapon. A longsword that normally threatens a critical on a roll of 19-20 would now threaten a critical on a roll of 17-20. A weapon that would normally threaten a critical on a roll of 20 (i.e., only 1 out of 20) now threatens a critical on a roll of 19-20 (i.e., now 2 out of 20).
Use: Automatic.
If The threat range of a keen weapon is already doubled, increasing to triple with this feat.
This feat can be selected multiple times, applying to a new weapon category each time.