Blowgun Mastery

Prerequisite: Proficiency with blowguns

You have learned to perfect your technique with a blowgun, as well as how to craft an incapacitating poison to coat your needles. You gain the following benefits:

• Increase your Constitution score by 1, to a maximum
  of 20.
• When you attack with a blowgun, you can use your Constitution modifier instead of your Dexterity modifier for the attack roll.
• When you hit with a blowgun, you deal piercing damage equal to 1d4 + your Constitution modifier in place of its normal damage.
• As an action, you can coat a number of
  blowgun needles equal to your proficency
  bonus with a potent sleeping poison. When
  you hit a creature with a coated needle, the
  creature must make a Constitution saving throw
  or fall unconscious for 1 hour. The save DC for this effect is equal to 8 + your Constitution modifier + your proficiency bonus. Once you use this ability, you can't use it again until you finish a long rest. The poison becomes stronger as you learn how to exploit the weaknesses of your target. Creatures automatically fail the saving throw against this poison if its challenge rating is at or below a certain threshold, as shown in the Poison Potency table below.