So, in the game Pokemon XY, there appears to be quite a dangerous†glitch in Luminosity City. It looks like when you save in that city, the game will freeze up. Currently, there doesn't seem to be a way to restore the game after the glitch, aside from resetting it, which then means that you'll lose all your data. Some people, however, reckon that starting the game with the wi-fi switch in the OFF position does work, so that could be worth a try.
Please spread the word around if you can and add any solutions you're aware of, so hopefully people will be able to avoid this glitch - I'm lucky that I didn't save in Luminosity (aside from in a Pokemon Center, which apparently isn't affected by the glitch), but I'm sure others will save in there, and maybe less will if they see this post.†
Some more information on the problem:
www.kpopstarz.com/articles/453Ö†(video of glitch)
purplepeepbits.deviantart.com/Ö†(someone talking about problem)
www.inquisitr.com/993239/pokemÖ† (useful, detailed explanation)
www.gamefaqs.com/boards/696959Ö†(a thread where quite a few people are talking about the issue)