Poison Attack

Poison Attack is a gem effect in Xenoblade Chronicles. It grants a percentage chance that the user's auto-attack will inflict for 10 seconds, dealing extra damage every 2 seconds (for a total of 5 extra hits). Unlike the debuff's normal effect, the damage done is equal to the gem's value, rather than based on the initial damage dealt.

Overview
Poison Attack is just an extra source of damage; it can be placed on anyone who wants to deal more damage without having to worry about extra aggro (as it's a debuff). It's the best of the four damage-debuff-auto-attack gems by a significant margin, dealing the most damage both per-gem and at the combined cap, but is also by far the hardest to get.