Staff Mastery is a skill in the Hell Fire skill tree of the Mage class.

Skill Description: Increase your magic attack for x% when you use a staff.
Required job: First Job
Required points: 0 points in Hell Fire
Skill type: Passive Skill
Weapon Required: Staff
LevelEffect (x)
1 3%
2 6%
3 9%
4 12%
5 15%

Important skill for all damage dealing mages, even if you are not primarily focused on the Hell Fire tree. An increase in damage is not something to avoid.