Double Dan effect: Double the experience gained by brushing monsters in one hour. Shuangdan is the most powerful in the use of copies of Zhenlong chess. Double experience+offline experience has greatly improved the level.

How to get it: Dan wants to join the guild and exchange it with a helper from the guild store. Each pair of Dan needs 35 points of tribute. (PS: You can join or create a guild after level 40. Tributes can be obtained by helping wars, rare events from heaven, etc. )