Each hero has specific cards that can be equipped. Consider building a balanced deck. Use Fast cards when an enemy has only a small amount of health. Always have a shield card and healing card in your deck. One of each for each of your heroes should be enough, and supplement them with high damage/effect cards and quick cards. Element cards can equipped to your heroes. Each hero has an elemental affinity. Specific elements are stronger against other elements, but also weak against another element. Consider having about half or half + 1 element cards to get a bonus effect. Also have some neutral cards when facing elements you are weak against.