Needs review
Source: Book of Vile Darkness

Description: After prolonged exposure to a poison or toxin, the character has rendered themselves immune to it.

Prerequisites:

The character is immune to one specific poison (chosen by the DM or the character's player), whether available as a blade poison, the venom of a specific creature, or one other toxin. The character also gains a +1 circumstance bonus on saving throws against other poisons.