You can dent and weaken armor with the impact of your mace, rendering it less effective.

<php>echo “<b>Prerequisites:</b>”;</php> Weapon Specialization (Maces)
<php>echo “<b>Benefit:</b>”;</php> Whenever you score a critical hit against a creature with a mace, that creature’s armor bonus (or natural armor bonus, if no armor bonus) is decreased by 2 until the end of the encounter. This feat cannot drop a creature’s armor bonus or natural armor bonus below zero.