Gruesome Butcher (Story)Source Agents of Evil pg. 9
You dedicated yourself to the cause of slaughter against a specific group or people, either for country, for vengeance, or perhaps just for sport.
Prerequisites: You must have been rendered unconscious and left for dead on a battlefield between warring factions or have the Child Soldier or Drafted background.
Benefit: Select a particular nation, organization, or humanoid subtype (such as Cheliax, Eagle Knights, or goblinoids). You gain a +4 bonus on Sense Motive checks to determine whether a given creature is affiliated with that group and a +4 bonus on Bluff and Diplomacy checks to conceal your animosity toward members of that group.
Goal: Deliver the killing blow to a number of your hated foes whose combined Hit Dice total is equal to 10 × your current character level.
Completion Benefit: You gain a +2 bonus on Bluff, Knowledge, Perception, Sense Motive, and Survival checks against foes of your selected type, and a +2 bonus on weapon attack and damage rolls against them. These bonuses stack with a ranger’s favored enemy bonuses.
Special: By meeting the goal of this feat, your name becomes known to your enemy. Creatures of your chosen enemy faction gain a +1 morale bonus on attack and damage rolls against you should they become aware of your identity with a successful Knowledge (local) check (DC = 10 + your character level).