Double Attack
From Xeliki
Double Attack:
Basic thief skill; No prereqs
Gives the chance for a single attack to do double the damage. Increasing the level of the skill increases the chance that a double attack will happen.
The chance of a double attack happening is equal to (SkillLvl*5)%
This is the most basic thief skill and regardless of thief build, you should use your first 10 job levels to max out this skill.