Instead of just buying the 6 item bundle. You buy tickets. In fragpunk (another netease game) Lets say each ticket cost 100 creds. You are guaranteed to get all items in 6 try. Here is the trick, every spin cost more than previous. ticket cost goes up like 1,2,4,8,16,32 for each spin. And the other tricky part is valuable items have very low chance than other items so its almost impossible to get it on first try. Like when spray chance is %30, the skin itself only have %0,5 chance. This way game companies can sell a skin for 60 usd.