Needs review
Source: Heroes of Horror

Description: In addition to your studies of the darkness, you have spent time studying giants and fey.

Prerequisites:

You can use your dark knowledge on giants and fey. You use Knowledge (nature) for dark knowledge checks regarding these two creature types.

Normal

Without this feat, a character with dark knowledge can use that class feature only on aberrations, elementals, magical beasts, outsiders, and undead.