Needs review
Source: Masters of the Wild

Description: Choose one favored enemy that is immune to critical hits. You know how to place blows against this opponent for best effect.

Prerequisites: Base Attack Bonus +7, Favored Enemy Immune to Critical Hits

Whenever your attack roll against this favored enemy would otherwise be a critical hit, you inflict +1d6 points of extra damage per damage die that your weapon would do on a critical hit. In addition, your favored enemy damage bonus applies to this creature type normally.

Normal

Creatures that are immune to critical hits are also immune to the favored enemy damage bonus.