Nocturnal Caster

(Tome of Magic, page 137, DnD 3.5)

[General]

You are empowered by darkness, making your abilities stronger at night.

Prerequisite

Ability to cast mysteries or a spell with the darkness descriptor

Benefit

Choose one path of mysteries or school of magic to which you have access. At night, the save DC of all associated mysteries or spells increases by +1. This bonus stacks with similar bonuses, such those from the Path Focus or Spell Focus feats. The ambient light is irrelevant, nor does it matter if you can see the sky. Only the actual time of day matters.

Special

You can gain this feat multiple times, but its effects do not stack. Each time you take the feat, it applies to a new school or path.