How do you get youre vivasaures to rank 12 in fossil fighters

Well first you have to be a master fighter. Then you have to have a good team like Dynal in the front guan on the top and compso on the bottom and they all have to be rank 11/12. Finally you have to keep battling your friends such as Rosie and Dr Diggins. To rank up all the vivosaurs you put them in the 2 back spaces. Hope this helped!