Mystic Vale is an interesting take on the deck-building genre, as you actually change your cards in your deck, instead of changing the overall count of cards in the deck itself. In the physical world, this relies on sleeved cards that you'll insert transparent other cards into. However, in the Digital version that's available now, it is as simple as changing the cards for "real." You can download and play this version now.
From the announcement:
Mystic Vale is a deck-building card game, in which 1 to 4 players take on the role of druidic clans trying to cleanse the curse upon the land. Each turn, you play cards into your field to gain powerful advancements and useful vale cards.