I see that you have added sort options to selecting dragons for the challenge fights. I have several friends who at some time or another downloaded your game but only a few still active so I use these as opportunities to rank up my dragons. Sorting by element or rarity is ok, but I would rather see an option where you can choose ranking so I don't have to scroll down so far looking for those I am trying to rank up.
Also, I often go to dragon book to be sure I haven't missed feeding any new dragons I've hatched, there it would be nice to be able to sort by level and then choose either high to low or low to high, depending on if I'm wanting to be sure newbies are all fed up to level where I want them, or if I have just bought the 4x food pack and want to raise up my highest dragons a level or two.
P.S. it would be nice also to know by looking at the dragon profile in the dragon book if it has been fed 1\4, 1\2, or 3\4 of the way to the next level. I sometimes am able to partially feed up my higher level but then forget which ones I was working on the next time I have a large enough quantity of food to make a difference, whether it be because I received another strong epic or legendary dragon in the meanwhile or if it has been a few days to grow more food. Maybe under the 5 stars can be a space for three dots that can be colored when each quarter feeding is fed to the dragon.