You can get some bonuses by using referral codes. Invite friends by giving them your code and they get one Legend CP Ticket and you will get an invite coupon and an elixir. The invite coupon can then be exchanged for a special R card that can be evolved all the way to SSR.
You can find the referral code by going to "Mypage" and scrolling down where you can find text which will lead you to input your friend's code or which will lead you to a page where you will see your invite tokens.
Use the comment function on this page to share your referal code.