Mempter's Barrier

This spell is similar to the 5th-level spell, wall of force, except a barrier is one-way, preventing things from coming in, but not from going out. It allows those protected behind or inside the barrier to attack those beyond, yet still prevents the outsiders' attacks from coming in. The barrier is invisible, immobile, and totally unaffected by most spells, including dispel magic. Blows, missiles, cold, heat, electricity, spells, breath weapons, etc. cannot affect or pass in through it, although dimension door, teleport, and similar effects can bypass it. A disintegrate spell, a rod of cancellation or a sphere of annihilation will immediately destroy the barrier.

The wizard can, if desired, form the barrier into a spherical shape with a radius up to one foot per level or to an open hemispherical shape of 1.5-foot radius per level. The barrier must be continuous and unbroken when formed; otherwise, the spell fails. The caster can end the spell on command.

The material component is 5,000 gp worth of powdered diamond and a mirrored lens.

Notes: Unique to Mempter, so far as is known. (Updated from Polyhedron Newszine.)