After the you defeat the Ogre Marauder in the Town of Folksvangur, you get the opportunity to choose one of 4 different Classes. Your Class will influence your battle-style in granting you access to unique Skill Cards for your deck.
Classes can be changed any time by using Class Selection Crystal. It can be obtained after boss fight or bought for 88 Gold.
The Warrior Edit
~The Warriors draw on their strength to inspire courage in one and all. They can not only use their skills to rally their own creatures, but also to directly inflict damage on enemy creatures.~
On the battlefield, a Warrior will use Skills like Encourage and Protect to strengthen the troops Attack or Defense. His Commands can shift the way troops are attacking or taking damage. Command: Vigilance is a good example and can be a real live saver if the enemy has reached your Hero and your troops need to attack from behind. Direct damage Skills like Slash are useful in almost any situation and can eradicate an enemy unit from the field.
See also: Full list of Warrior Cards
The Ranger Edit
~The Ranger's senses are exceptionally keen, and their skill of inflicting damage to enemy heroes is widely renowned. Their special skills to control a battlefield are a tremendous challenge to their opponents.~
Control is the Rangers greatest tool. He can influence cards in the enemy's hand or even his own through Skills like Swift Death and Premeditation; and doesn't shy taking some damage to gain an advantage. Troops on the battlefield are shifted around through his Disinformation, or even taken out of the field directly. The Ranger can use Tactics to weaken the enemy, like Tactic: Sunder Armour, and uses poison for extra damage.
See also: Full list of Ranger Cards
~Mages pursue the research of magical energy tirelessly, and their prime aim is to increase the damage they can inflict. Moreover, they can assume control of their opponents' creatures.~
As master of the elements, the Mage commands many direct damage skills like Fireball or Lightning Storm. A number of his skills also have negative effects on troop movement, like Petrify and Frost Nova, thus hindering the enemy to reach your Hero. The Mage is great at negating the enemy troops strength, or, using Charm, even stealing a whole enemy unit for a turn. Once the enemy troops are frozen in place and harmless, the Mage can give his troops Hermes Wings to fly over the battlefield towards the enemy Hero.
See also: Full list of Mage Cards
The Priest Edit
~The Priests are devout believers, and have powerful healing and defence skills at their disposal to assist their own creatures. They can pray for burning light to scald their opponents' forces.~
The power to heal and give extra Life is the most obvious strength of the Priest, wether he uses Cure on a single creature or the Ring of Healing to cure a whole area. His Blessings can give troops positive abilities like Blessing: Armour or Blessing: Regenerate. He can even bring creatures back to to live using Resurrection. While most of the Priest's skills are defensive, he puts all his might in the strike if he uses Smite against his enemies, thus ignoring all damage reduction and even preventing Undead creatures from returning.
See also: Full list of Priest Cards