I know it has been mentioned before but not in over a month.
Some cards require supper rare cards for evolution.
2 ideas would like to see both of them proly not going to happen
1) add a 3rd card option to be able to use as evolution fodder
2) add a 4 and 5 star evolution fodder card it would not be a common card to get and you would likely need more than 3 to evolve the card you want, but they can be used to evolve any card quantity may vary though.