Official in-game currency includes Mobacoins, Gold, and Friendship points.
Mobacoins are purchased in the in-game Store via credit card, iTunes/Appstore credit, or Android/Google Play credit. Mobacoins can be used to purchase items such as Stamina Drinks, Battle Drinks, Magic Traps, Skill Removers, Escape Portals, and Devil's Spears. It can also be used to purchase Card Packs to boost your deck with more powerful cards.
Gold is most often gained by completing Quests or through Battle with other players. It is also possible to sell any card for gold. Gold can be obtained through some event missions. Gold is consumed in the process of Fusion. Gold is an important aspect of the game, and a competitive player will spend it wisely.
Friendship points are gained when you either greet another player or another player greets you. The fastest way to gain Friendship points is to go through your Friends List and greet each of them. It is possible to greet any player when you visit their page. Friendship points are used to buy Friendship Card Packs that include 3 random Normal, Normal+, and the occasional Rare cards.