A valid deck contains exactly one Hero card and 39 or more compatible non-Hero cards. They must either belong to your hero's faction, either Human or Shadow; their class, either Warrior, Mage, Hunter, Priest, Wulven, Rogue or Elemental; or be Neutral. For example, if you chose Gravebone as your hero, then you may only add cards from the Shadow faction, the Mage class, or those denoted as Neutral to your deck.

There are currently 32 legal Heroes to choose from in Shadow Era (Carmila is a restricted promotional card only). 16 are Human and 16 are Shadow.