[Scripting Question] How do you restrict certain moves to mega evolution only on certain Pokemon?

[rizneeeeee]

I wanna add a new move to my game which is simple enough however I want it to only be usable on a certain Pokémon if they are mega evolved and the game not allowing them to use saying like "You need to mega evolve your Pokémon before using this move!" while still being usable for other Pokémon that aren't mega evolved if that makes sense.