Spellbook needed to learn 'Focus Skill Mastery'.

Required:
Treasure Hunter - Lv. 70
Hawkeye - Lv. 70
Silver Ranger - Lv. 70
Abyss Walker - Lv. 70
Phantom Ranger - Lv. 70

To obtain this item, hunt the Conjurer Bat found in Blazing Swamp.