Wall Of Gloom

Illusion (Shadow) [Darkness, Fear, Mind-Affecting]; Warlock Invocation
Level: Lesser, 4th lv.
Components: V, S
Casting Time: 1 standard action
Range: Medium (100+10ft/lv)
Duration: Concentration + 1 round/level
Saving Throw: Will
Spell Resistance: Yes

You create a barrier of ominous shadow that obscures vision and deters passage. Creatures in squares adjacent to the wall have concealment against attacks from the other side, while creatures more than 1 square away have total concealment. Although the wall is not substantial, a creature with 6 or fewer Hit Dice must succeed on a Will save or be halted at its edge, ending its move action (though a creature can move away from the wall or attempt to move through again if it has a second move action available).
A creature can attempt to pass the wall any number of times, but each previous failure imposes a cumulative –1 penalty on its Will save.
Wall of gloom counters or dispels any light spell of equal or lower level.
Material Component: A bit of fleece from a black sheep.

(Complete Arcane, Page 134)