Diode of Force (3.5e Spell)

The demon hordes piled up against the barrier at the cave's mouth, only to be repelled by the archers safely behind the wall.

This spell functions as wall of force, but only one way. One side of the wall allows things to pass through while the other remains invulnerable. For each creature, spell, or object over 50 lbs in weight which passes through the wall the duration is reduced by 1 round. If the duration is reduced to 0, the spell ends.

Wall of force can be made permanent with a permanency spell at the cost of 4000 xp.

Material Component: A pinch of a clear gem and a shard of one way mirror.