The Master's Reward is a Cooperative Mission reward given to players who exceed the "Expert" completion criteria for a mission for the first time. In Normal Mode, it almost always grants 500 more XP than the Expert's Reward (the only exception being Chahbek Village (mission)), 50 more gold, and one more Skill Point. In Hard Mode this becomes 1000 more XP, 200 more gold and like Normal Mode, 1 more Skill Point.
A character can earn the title Protector of Cantha if they earn a Master's Reward for all the missions in the Factions campaign and Protector of Elona if they earn a Master's Reward for all the missions in the Nightfall campaign. They are analogous to the "bonus missions" of Prophecies Campaign.