Boon of Poison Mastery
Prerequisites 19th
You gain the following benefits.
Ability Score Increase. Increase one ability score of your choice by 1, to a maximum of 30.
Antitoxic. You have Immunity to Poison damage and the Poisoned condition.
Perfect Poisoner. Once per turn, when you roll dice to determine Poison damage a creature takes from your attack, spell, or feature, you can instead use the highest number possible for each die.
Sources
Forgotten Realms: Heroes of Faerûn p. 43