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Z-Moves were a complete flop of a mechanic
>Visually the mechanic are basically just battle versions of the Spectacular Talents from ORAS
>Only Kanto and Alola mons got unique Z-Moves. 3 out 18 are also just for the Pikachu line.
>Most unique Z-Moves have no secondary effect and are there just for the animation
It's like they created a mechanic without having any idea about what it could be so they decided you would have a move that can only be used while holding a not-Mega Stone. EXCEPT THAT THE POKÉMON DON'T HOLD THE CRYSTALS IN UNIVERSE, holding the stones is just a gameplay abstraction because they wanted to balance it out like Megas. The mechanic makes no sense in universe and forces the roleplay player character to act goofy and do silly dances for power-ups. At least Megas have the goofy, the cute and cool ones for every player to feel just right with their choices.