Players earn by completing various tasks. Unlike other events, there is no cap on the amount players can receive with each task. As higher level players are able to collect more gold and food, the amount of players receive depends on the amount of coins they have collected to that point: players having earned lots of will earn less for each task.
The tasks from which players earn include: collecting gold, collecting food, winning multiplayer battles, and breeding monsters. With breeding, the higher the rarity and longer the breeding time, the more players earn.
Players spend by flipping cards. Players earn rewards with each card flip and, eventually, earn the monster. The cost for each card flip increases each time. Players may also spend to immediately claim the monster. The cost reduces with each card flipped.
Despite the appearance that the cards are shuffled, the results of each flip are completely random, meaning whichever card a player selects is irrelevant to the result. It is important to note that the chances of each reward are not necessarily equal. While it is possible to obtain the monster on the first flip, it is less likely than other rewards.
Most 72 Hour Challenges have 3 monsters that players may attempt to get, listed in order from least to most expensive. Sometimes, higher level players are offered ranked up versions of the monster.
See previous 72 Hour Challenges.