Twilight Hex (Evil Weather Supplement)
From D&D Wiki
 What is the Twilight Hex?
The Twilight Hex is a powerful curse unleashed upon a location of mass murder or genocide. The powerful hex can only be dispelled by the most potent magics, and so a Twilight Hex often stands long after the structures, city, or ruins it encompasses pass into dust. Within the location, all light is muted and colors seem grey and washed-out. Further, any living creature that enters the area is overcome with dread. Finally, a Twilight Hex nefariously twists reality to favor the energies of death and rot while hampering those of healing, renewal, and good, which makes areas with a Twilight Hex favored hideouts for evil cults and monsters with horrid intentions.
 Game Rules
Area: Varies. Usually between a thousand and a million square feet. (d100 x d100 x d100 square feet; minimum 100 square feet).
Evil Magic Bolster: The numerical descriptors (including range, duration, targets, and damage) of all spells with the evil descriptor are doubled when cast within the area of a Twilight Hex. Likewise, the numerical descriptors of all good and healing spells are halved.
Hindered Sight: All normal visibility within the area is reduced to 1/2 normal.
Aura of Dread: All living creatures that enter the area of a Twilight Hex are automatically shaken (no save).