So, considering how Megas and Z moves both require held items, is Rayquaza theoretically the only mega that can use a Z-Move?
>>30213090
In theory yes.
In reality, it can't Mega Evolve while holding a Z-crystal.
The game is hard coded to stop Rayquaza from mega evolving, if it is holding a Z crystal.
>>30213090
Ash Greninja is technically a mega and so is Wishiwashi's schooling form and they can both use Z moves while transformed.
>>30213239
I'm pretty sure ditto can use them while it's a mega. Never tried it.
What if someone gives him a Z-crytal after he mega evolves using trick, etc?