Pro tip for ranking a dragon for your fighting team (C- to A+). Winning rescue fights counts for ranks. With these easy rescue opponents it is easy to get some more wins there. You have 7 days for each rescue. Put in that one strong, high level dragon that you want to go up in rankings with a weak team. That makes it possible to let him win several fights. Then wait the 4 hours cool down time and do the same again.

Thanks @Bettina!
As usual I rush through the rescue but now you gave me a new strategy!