I'm definitely more into ORAS than XY.
But without getting too technical, a powersaver is a little tool that you plug into your computer, then insert your game cartridge into and it basically modifies the physical coding of the game for just about anything. I mostly use it modify Pokémon to make them shiny and clone them for giveaways; but, I've also used it to make some items and even to generate Wonder Cards for past event Pokémon.
Unfortunately, most don't look too kindly on people like me who use a powersaver because all you do is check a couple of boxes and you have a shiny instead of spending hours hunting or breeding for one. You also run the risk of corrupting your game; but, that's why you back it up before using it and then let it automatically back up each time you use it.