You are well-trained in wielding shiftsilver weapons, maximizing their shiftsilver quality to deadly effect.
Prerequisite: Shifter, base attack bonus +8, two other shifter feats, must have crafted your own shiftsilver weapon.
Benefit: Whenever you score a critical hit with a shiftsilver weapon you crafted against a creature with DR/silver, your shiftsilver weapon temporarily turns into liquid silver, rending flesh from the inside out and dealing 2d4 points of Constitution damage.
Special: A fignter may select Shiftsilver Mastery as a fighter bonus feat.
Source: Dragon Magazine #355 (Page 76)