When a yellow light explodes, the 3x3 area centered on its explosion area should become permanently lit up. Conversely, when a black light explodes, the same area should become permanently darkened.

A monster that emits non-persistent darkness in an area, just like how various monsters shed light in an area.

Various monsters have been suggested for this effect:

• Black lights are one that already exists; this would invert its current light radius of 1 into darkness.
• A shadow dragon.
• A darkness elemental, which in addition to shedding a radius of darkness, also permanently darkens squares it moves throught by removing the lit state.