Shadow Era is a freemium virtual collectible card game in which players take turns summoning allies, using abilities, and attacking in order to drive their opponent's hero to zero health. Each match is a duel between two players: you and either an AI opponent of your choosing or another online player matched to you automatically (passworded manual match creation is also supported).
Version 2, i.e. "Dark Prophecies", incorporates the cards found in version 1, i.e. "Call of the Crystals", with a whole new set of cards, making for twice the possible variety in every match (apart from hero cards, which merely have alternate designs). Also new in Dark Prophecies is a "Meltdown" mode in which players submit gold, the non-premium currency, in order to enter a contest match while selecting from randomly generated and mixed-up card sets. High scorers in Meltdown earn a share of the gold jackpot, which can be used to purchase specific cards in-game. All cards are individually available to purchase with gold in this manner, but packs of cards can be purchased with premium "crystals". Somewhat exceptional is the ability to "earn" premium currency in Shadow Era by filling out online surveys and the like, for those with more time than money.
Sam's Protip: Having multiples of a hero card is futile, so if you end up with them, sell all but one off to earn gold for other cards.