what a ride…whoever calls this challange ezpz is drunk or drogged 
i know that others have pointed to some urls for help but its much more than just that.
hint:
as some mentioned before: search for php obj injection and take some parameters from there and start your enumeration
when you find the right parameter, put your s**i after the ID.
Now the tricky part begins, follow the suggested github pages but you will need to send the right query to JOIN the game. the waf is picky.
hope its not to a spooiler.
i did it manually and it took me 2 days. PM me if you need help.