The new Hearthstone expansion, Descent of Dragons, has just been revealed and with it we will see a new type of card: the side quests.
In order to fight against the E.V.I.L League that woke Galakrond, the Adventurers get a new type of card: The sidequests. They are reserved to Paladin, Druid, Mage and Hunter.
Like existing quests, they appear in your starting hand. After completing it, you get a pretty significant effect on the game. They are normally easier and faster to achieve than the previous ones.