English (Source)
Challenges can appear when expanding the map. You're able to select from several challenges, making the game more difficulty for a few rounds, but in exchange for an immediate reward.
Chinese Translation
在扩展地图时有几率出现挑战。你可以从多个挑战中选择，使游戏在数个回合内更困难，但作为交换可立即获得奖励。