Benefit: When you score a critical hit with an attack, you can forgo dealing extra damage to instead deal 1d4 Constitution damage. Weapons with a critical multiplier greater than x2 deal +1 ability damage for every additional multiple (thus Shock delivered with a greataxe deals 1d4+1 Constitution damage).

Special: You can apply the effects of only one critical feat to a given critical hit unless you possess Critical Mastery.