|Each of the three characters has different behavior in battle.
The Mage is bad at close range, but excels at long range. She can cast a variety of spells that will deal a lot of damage while she can remain relatively safe. The Mage requires upgrading to be used effectively.
The Warrior is focused on strength. His high strength and defense allow him to do give out large amounts of damage while not taking too much himself. The additional skills he learns are very versatile. When upgrading him, consider lessening the cooldown so that he can be used more frequently.
The Monk is very good at close range, however his defense is not as good as the Warrior. His good speed can be used in hit and run tactics to mitigate damage. Upgrade him, especially his Critical Hits abilities to allow him to take down powerful opponents.