20ef1efc_Spiderkind_Chapter____D_D_Wiki__Benefit
[Feat] Staggering Critical [Prerequisites] Ability to score a critical hit with a weapon group on the roll of 19-20 [Benefit] 
Your critical hits sent your foes reeling.
Feats (Arachonomicon; the Book of Spiderkind Chapter) - D&D Wiki
Benefit