The allies of your foes are especially afraid of your critical hits.
Prerequisites: Cha 13, undead type, Death Master, Daunting Presence, Improved Critical, base attack bonus +1.
Benefit: Whenever you score a critical hit with a melee attack against a living foe, creatures within 30 feet that are allied to that foe are shaken for 1 minute. This is a mind-affecting fear effect.
Source: Libris Mortis, page 26.