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.