How come my rayquaza learned dragon ascent but he won’t mega evolve in ultra sun?

Question

I’ve got a rayquaza that learned dragon ascent but no matter what I try he still won’t mega evolve

Comments

Can you mega evolve a Pokemon that's not Rayquaza?

---

Is it holding a Z-Crystal?

---

I'm pretty sure a Pokémon holding a Z-Crystal can't Mega Evolve, even if it doesn't need an xxxite to Mega Evolve.

---

Yes I can mega evolve other pokemon, no its not holding a z Crystal

Answer 1

There are three possible reasons why a Rayquaza with Dragon Ascent might not be able to mega evolve:

1. You've already mega evolved something else earlier in the same battle
2. Rayquaza is holding a Z crystal (even one that's not compatible with any of its moves)
3. You don't yet have the Key Stone, which you get by fighting Dexio at the edge of Poni Plains and Poni Meadow after you've beaten the league (without that, you can't mega evolve anything)

Answer 2

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.