With the Grung's racial trait Poisonous Skin, you can apply poison to your weapon as part an an attack:
You can also apply this poison to any piercing weapon as part of an attack with that weapon, though when you hit the poison reacts differently. The target must succeed on a DC 12 Constitution saving throw or take 2d4 poison damage.
Since crossbows are piecing weapons you could apply the poison to your Hand Crossbow. With the Crossbow Expert feat, you can attack again as a bonus action after attacking with a one-handed weapon, thus attacking 2 times in a turn with the Hand Crossbow. Same goes for the Extra Attack feature of a higher-level fighter with crossbows.
I am confused about the rules/phrasing of Poisonous Skin. In the One Grung Above sourcebook, "attack" is written in lower-case for this trait but has a cross-reference to the Attack action which is usually written in upper-case. I can see different scenarios how this works together:
- You apply the poison to your piercing weapon (crossbow) as part of the attack and the poison counts for every bolt you fire with this weapon
- You apply the poison to your bolt as part of the attack and can apply it again for the second bolt you fire with your bonus action, since the bonus action is an attack (lower-case) too
- The poison only works for the first attack and can't be applied until your next Attack action (upper-case)
Does the Grung's racial feat poison work on all bolts when using a crossbow, whether you apply it on your crossbow or each individual bolt during your turn or does it only work for the first bolt you release and the poison can't be applied again until your next Attack Action (upper case)?