Nightmare

A nightmare rune creates minor phantasmal alterations to a weapon's appearance so that those who look upon it see subtle reminders of their deepest fears. An arachnophobe might interpret the cross guard of a nightmare longsword to look like curving, twitching spider legs, for example, while someone who's afraid of sickness might see a nightmare club as a diseased length of bone crawling with flies. These images are all in the mind of the observer, but they also infuse the weapon with additional power. When you hit with a nightmare weapon, add 1d6 mental damage to the damage dealt. In addition, on a critical hit, the target becomes Nightmare to your specifications.