Each Hero has up to four skills: a Basic Skill, a Passive Skill, a Commander Skill, and a Special Skill. Skills are one of the most defining aspects of characters, and many skills are more effective when used in the right combinations.
A Basic Attack is a Hero’s default ability based on the character's class. Heroes rated Rare or higher have Basic Skills, which are more powerful versions of Basic Attacks. Basic Attacks and Skills do not cost mana. Each Hero class has a different Basic Skill which can be upgraded by collecting Shadow Essence from World Bosses and using them on Class Training at the Ancient Factory.
A Special Skill is a Hero’s activated ability. Special Skills cost mana to activate and are usually very powerful. Special Skills can have a wide variety of effects. Heroes gain skill experience every time they participate in a level, leveling it up to make it more powerful over time.
Passive Skills activate automatically. Although they can be easy to ignore, Passives can have a big impact on your effectiveness. Many passive skills require a condition to be met to trigger. For example, many Heroes have passives that trigger when they kill an enemy, and some Heroes have passive skills that trigger when they die.
Commander Skills are similar to Passive Skills in that they happen automatically. Commander Skills often change the battlefield or have an impact on the entire team. You can only have two Commander Skills active at once - the one from your selected commander, and the one you receive from the allied commander (or guest) you bring with you.