A Z-move is a special move used by a Pokemon: Super powerful moves that can only be used once in a battle. They are like “Limit Breaks” in Final Fantasy or those super hidden moves you see in some Anime.
What Pokemon can use Z-Move?
Z-moves are game changers that has the potential to change the flow of battle with in one turn. They are divided into two categories: Type-specific which can be accessed by any Pokemon as long as they are the same type as the move and Pokemon Specific like Pikachu’s Catastropika and Snorlax’s super adorable Pulverizing Pancake that can only be accessed by specific Pokemon.
How powerful it is
Z-moves do not have defined stats, rather, they just boost the power of the base move it partners with. For example, A Z-move Tackle will receive a boost in relation to its base power which is 40 and will retain its physical property, the same will apply to 80 base power Water attack with special property and so on and so forth.
Z Status Move
Z Status Move are special bonuses distributed into different moves. These are secondary effects like boosted defense or boosted attack after doing Z moves that is different across the large movepool of the entire game. For example, A Z-move Splash now grants three stages of Attack increase! Perfect for those Dragon Dance Gyarados builds!
How to Use
With that said, Mega Rayquaza, the strongest Pokemon in the entire series that does not require a Mega Stone to Mega Evolve cannot do a Z Move after Mega Evolving or Mega Evolve after doing a Z Move. That’s totally fair because the dude got banned from the ban list after all... let that sink in. Maybe Gamefreak thought you can’t really ban him beyond that tier.
Z-Moves are very similar to Mega Evolution when it comes to requirement: they require a ring and a crystal, one item for the Pokemon and one item for the Trainer. This means that no Mega Pokemon can do a Z Move which is great game design, just imagine what a Swords Dance Mega Salamence can do with a Z Move!