Feat
Acquired Resistance
Repeated exposure teaches the body a toxin's language
The character develops immunity to poisons they handle regularly. Immunity is learned one poison at a time: familiarity with nerve venom grants no protection against Drow Sleep or Black Flower.
Acquiring immunity
The character must personally prepare, extract, or apply at least one dose of the same poison during three separate rests. After the third handling, add that poison to the character's acquired resistances. Deliberate poisoning is unnecessary; the feat represents trace contact, fumes, and precautions gradually adapted to the substance.
The character then becomes immune to that poison: exposure requires no Save and applies none of its effects. Immunity also covers the same poison enhanced by Poison, because the magic increases its strength without changing the substance the body recognizes.
If a level 5 poison is transformed into an effect from another toxin family, the GM may treat it as a new preparation to master. A new antidote, a substantially altered recipe, or a mixture of several toxins also counts as a distinct poison.
There is no limit to the number of acquired immunities, but each requires its own ingredients, three separate handlings, and time in play. Unknown poisons, diseases, acids, and magical effects not based on a physical toxin are never covered.