I’ve got a rayquaza that learned dragon ascent but no matter what I try he still won’t mega evolve
There are three possible reasons why a Rayquaza with Dragon Ascent might not be able to mega evolve:
I think it has something to do with the second story. this happened to me too, and I think you just have to beat team RR. this gives you access to other legendaries, such as the Kyurem forms, as well.