Opaque Foreground Effect

[Snarf Blaster]

Trying to find, or create, an effect that goes over the map to simulate a cursed area. Is this a function of the game that I'm missing or does this lie in a script? Any help would be great.

 

[Psycoris]

What kind of effect? Something animated, a parallax, a symbol or tile. Does it need to move. How big a single tile or a maps worth like a swamp. A one shot for a single map or reoccurring.