Special Rules

Nine Hells and Abyss

These special rules govern adventure parties in Nine Hells or Abyss.

Creatures cannot be banished or repelled because of their unholy status. However, they can still be damaged because of it and ethereal creatures forced to materialize. However, any effect depending on unholy status causes on a d6 roll 4+ one damage to caster! (Banish Evil and Bless, mainly)
Holy things like holy blades are obvious and hated and feared by all inhabitants.
Arch-devils (Hell) or Demon lords (Abyss) answer to summon only if they want to.
A wish is granted by the closest arch-devil (Hell) or Demon lord (abyss), and he may refuse to grant some wishes.
Magical items with spell-like effects use all rules for spells.
(Abyss only): A slain body might become inhabitated by a wandering spirit. Roll d6 at the start of each hour, and roll 1 means that the body is now inhabitated. Such a spirit must be first banished.

Creatures are immune to death magic at their own home plane
Non-native creatures are not summonable, unless very close. Native creatures summoned or conjured have their own will.
Detect magic and evil are quite inefficient. Everything is magical and evil, but some more magical things can be obvious.
A planar gate can only be opened to normal world. Unless near a conduict, the arch-devil of the level may prohibit this.
(Abyss only): Polymorph and regeneration spell might have (d6 roll 1-2) unexpected results, chaotic mutations and such

(Abyss only): Halve Faith level for any Miracle dependent on it, like Turn Undead or Banish Evil
Evil Ward does not help in Nine Hells or Abyss
Banish Evil and Bless cannot banish devils (Hell) or demons (Abyss), but may be used to force ethereal creature to materialize. Each time used, they damage priest on a d6 roll 4+.
God cannot hear prayers of their followers. No need to test any divine intervention.