During your adventures you've slowly gotten more in touch with your sadistic side.
Your attacks become more violent and visceral, leaving showers of blood and piles of innards in your wake.

On landing a critical hit or a killing blow on a creature, allies of that creature with atleast 8 INT that could see you must make a Charisma save with DC14.
On a failed save, they become frightened until your next turn.
On a success the creature manages to keep it together, but the DC for its next saving throw against this feat increases with 2 on the next save and stacks with every subsequent success afterwards.

Feel free to graphically describe how you maim your unlucky victim with your weapon/spell of choice when you trigger this feat.

(This feat is mostly meant for evil characters, but be my guest if you feel like playing a Paladin that disposes of evildoers in a particularly violent fashion)