>>20658699>[CITATION NEEDED]This is headcanon that was built as a hasty explaination attempt around the fact that so far none of the stone evolutions got their Mega evos.
It only lives on because of its value as a Poke-paranoia fuel and anons that throw it around from time to time just to piss off everyone who lends an ear.
Given GF's turn to 'less is more' direction when it comes to the size of new regional flavour, it is rather a matter of 'when' than 'if' for mega Gallade to happen as GameFreak will likely continue to make up for the reduced amount of new Pokemon via such gimmicks as new Mega designs for older ones.
