Impeding Attack( Complete Scoundrel, p. 78)
Your strikes render your target temporarily clumsy and awkward.
Sneak attack +4d6,
Your successful sneak attack imposes a -2 penalty on the target's Strength and Dexterity checks, as well as on any Strength – and Dexterity – based skill checks, for 10 rounds. If you use this feat a second time on a target before 10 rounds have elapsed, the effect of the first use expires. Using this feat reduces your sneak attack damage by 3d6.