Several players are reporting a game breaking bug in Pokemon X and Y which corrupts your save file, rendering it unusable.
The issue appears to be linked to Lumiose City. Players are reporting that after saving in the city and quitting the game their save file becomes corrupt. Upon attempting to restart from the save they are dumped in a half rendered city and their 3DS becomes unresponsive. The bug is being reported in both the European and Japanese versions of the game. You can check out a video of it below.
Nintendo is yet to officially acknowledge the bug, but it’s probably best to avoid saving in the city for now.