I was wondering why Pokemon like Pikachu changwd their stats? Or Alakazam. They were good Pokemon
Well this is just my two cents here.
I think it was to balance out the game a bit. Apparently they added Mega Evolutions to balance it out a bit. YEAH LIKE WE NEEDED MEGA MEWTWO AND MEGA BLAZIKEN
Hope I helped!
Like Artist KS said,they might have been changed to even the game out.However,most of the changed stats aren't that significant.Maybe they were added for no reason or maybe to make some Pokemon a bit stronger. here is a list of all the Pokemon whose stats were changed: http://www.serebii.net/xy/updatedstats.shtml