Keywords are: 'thief skill shadow mastery' Skill: shadow mastery Lvl 30 Thie (28%) (critical) Requires: cloak of darkness Group: Thief shadow disciplines Shadow mastery is a passive skill that allows the thief to use shadow skills more often, with less danger from the prolonged exposure to the shadow plane. If you know shadow mastery and monster lore, you will have a better chances of assessing the vulnerabilities and resistances of shadow creatures.