To get this, you need to make 100 line clear hexes, by putting four hexes of the same colour together at once.
Note For Hexic (Windows) players: If you have already done this requirement on the windows 8 version of the game, to get this to unlock, all you need to do is make
ONE line clear hex, and the achievement will pop instantly, assuming you're playing on the same save file via the windows Cloud. This means that you can get most of the Windows Phone 8 Hexic achievements out of order.