Those who enter the dragon's cavern will find nothing but a large mound of blackness, for Rahab is hidden by a form of continual darkness. The spell is not affected by anything save continual light, which will act as a light spell. In this darkness, Rahab has an armor class of -5. If the darkness is temporarly alleviated by the application of continual light, its armor class worsens to -2.
We could give it a kicker on the darkness aura--unholy aura, perhaps?--that gets removed if the darkness is dispelled with light. If daylight can't dispel it, perhaps sunbeam/sunburst?
Lords of Madness said:This spell is similar to darkness, except that those within the area of darkness also take unholy damage. Creatures of good alignment take 2d6 points of damage per round in the darkness, and creatures of neither good nor evil take 1d6 points of damage. As with the darkness spell, the area of darkness is a 20-foot radius, and the object that serves as the spell's target can be shrouded to block the darkness (and thus the damaging effect).
Damning darkness counters or dispels any light spell of equal or lower level.
Spell resistance applies to the damage dealt by this spell but not to the darkness area.
Presumably he already gets concealment, but we could go with total concealment if not an AC bonus...Damage in the darkness might work, but I was thinking another defense, like a profane bonus to AC for Rahab.