Mastery and Resistance

From FWpedia

Mastery and Resistance affect your attack strength and defense with certain elements. There are seven different types of masteries and resistances: Physical, Fire, Water, Wind, Dark, Earth, and Light. Your masteries and resistances occasionally raise a slight amount when you level up, but there is a quest you can do to level them yourself more quickly. See: Mastery and resistance training

Mastery and Resistance Items

Once you complete mastery/resistance training at your skill tutor up to level 20/40/60 etc., they will require specific items from you to break the training barrier. Each class uses specific elements for their attacks, and each element has a different item.

Physical: Invincible Blade
Fire: Flame Fervor
Water: Ocean Surge
Wind: Wind Pulse
Dark: Dark Spirit
Earth: Mountain Heart
Light: Radiant Light

These can be gotten from random monsters or quests, but the most reliable source is from your advanced training grounds Training Master NPC who can sell you items to help generate them as you attack certain dummies. Advanced Training Grounds requires level 40 to enter, and can be entered via either Gronny, Sophia, or Alain, depending on your race.