The caster creates a handful of invisible, nigh-intangible powder that attracts creatures from the Lower Planes.
Book of Vile Darkness 3.5
By Monte Cook
The caster can sprinkle this powder in a trail on the ground. Evil outsiders who come within 10 feet of any portion of this trail and fail their saving throws follow the trail as if affected by a compulsion effect.
Compelled fiends will follow a nether trail even into danger. For example, the trail could lead to a trap, a holy spell effect, or even a prison cell. If the danger is obvious, such as a Blade Barrier, the compelled creatures get another saving throw to resist.
A compelled creature only follows the trail to its end. So, if the trail leads to the edge of a cliff, the fiend goes to the edge of the cliff and no farther.
If a creature encounters the trail in the middle, it instinctively senses which direction is forward and which is backward. When the evil outsider reaches the end of the trail, the compulsion effect ends, and the creature cannot be affected by this particular nether trail again.
The trail can be obscured and destroyed by anyone who can see invisible objects. It takes a standard action to destroy 10 feet of trail, but an evil outsider must make its saving throw first.
Material Component: A urine-soaked holy symbol, which crumbles into the powder that creates the nether trail.