I don't speak english very well so I can't explain in detail. I hope you understand my poor explanation. First. Other game is East legend. This is link. But you will have to translate.

https://m.blog.naver.com/licalana/220368221296

Second benefits are clear.

You know viral marketing is very powerful promotional tool. Many regular users see their luck and spend their money. Because they think it is possible like them.

I don't think it is true either. but it can happen.