Mastery is your degree of proficiency in a certain type of action. The more actions you perform, the higher your bonus in the corresponding Mastery. There are currently 11 Masteries available, they are:
Increases the damage dealt by Swords. Get XP by battling with a Sword.
Increases the damage dealt by Staffs. Get XP by battling with a Staff.
Increases the damage dealt by Bows. Get XP by battling with a Bow.
Increases 100 HP per Mastery level. Get XP by performing Rebirth.
Increase the chance to catch a pet with rarity higher than Common. Get XP by capturing pets.
Increases the maximum limit of coupons that can be purchased. Get XP by participating in lotteries.
Increases the damage dealt to Raid Bosses. Get XP by joining Raid Battles.
BOAT BOMB MASTERY
Increases the damage dealt by Bombs. Get XP by shooting bombs at other boats.
Increases the chance of finding one more unit of an item in the Expedition. Get XP by collecting items in the Expedition.
Increases the chance of finding an item or Diamonds in greater quantity in Mystery Chests. Get XP by opening Mystery Chests.
Reduces the waiting time between harvests. Get XP by performing harvests.