Vulnerable

Debuff effect. For each stack, the target takes 1% more damage for 3 seconds. This effect stacks up to 20 times, and loses one stack on expiration.  Found on:
 * Vulnerability items
 * Frostbite items
 * Thunder-Forged weapons with 1st Degree Burns upgrade


 * Conduction - 4th core ability of Air Savants
 * Disorienting Smash - Vanguard Tier V enhancement
 * Improved Elemental Arrows:Shock - Elven or Ranger Arcane Archer Tier V enhancement
 * Shocking Vulnerability - Arcanotechnician Tier II enhancement
 * Smite Weakness - Warpriest Tier II enhancement
 * Strickened Form - Soul Eater Tier IV Enhancement
 * Avenging Cleave - Avenging Cleave Tier V Enhancement
 * Elemental Words - Henshin Mystic Tier I/II/III/IV Enhancement

See similar but apparently different debuffs:
 * Bound Fate & Grim Fate - Fatesinger epic destiny
 * Rebuke Foe - Exalted Angel epic destiny