Terrifying Slayer

This creature has mastered the slaying a creature in a horrifying and torturous way; ending the life in such a way those nearby consider it perverse. Once per long rest, when this creature makes an attack from being lightly or heavily obscured, if the creature is reduced 0 hit points they can trigger the Terrifying Slay ability. When this ability is triggered all hostile creatures within 30ft must make a DC Terror Wisdom saving throw; on a failure they become frightened.

DC Terror: 8 + Proficiency bonus + Dexterity modifier.