Pokemon has been around for fifteen years now, and many modern PokeFans, myself included, have been playing the series since its original North American release in 1998. Back then I recall Pokemon Red and Blue being much more difficult than Pokemon is today–the Elite Four's Agatha, with her Gengar, springs to mind as notoriously hard to beat–but much of that difficulty probably had to do with age. I was only nine years old, after all. Now, however, I have little trouble clearing every Pokemon game, most recently Pokemon X and Y, which I found to be the easiest Pokemon adventure I've ever gone on.
Part of the problem is, as an adult, it's easy to figure out Pokemon's elemental system and exploit the hundreds of trainers you fight during the course of any given Pokemon adventure. Furthermore, Game Freak and Nintendo are reluctant to add a proper higher difficulty to these games. Of course, the Pokemon games are known for being customizable to the player's experience, so it's quite easy to add a few self-imposed rules to make each adventure more challenging and therefore more engaging.
Below are six ways to make Pokemon X and Y more difficult. I've found they work well; be that as it may, if you ramp up the difficulty in some other way, let us know in the comments!