As much as I enjoyed Pokemon X & Y, even I will admit that the games are kind of on the easy side. If a lack of challenge is a thing that bothers you, good news, chief. There are things you can do to keep things interesting in Pokemon X & Y.
Let's start with a tactic I mentioned in my tips article and go from there.
Don't Grind (Much)
I know, I know. Choosing not to grind in a role-playing game with levels and experience points? That's kind of like choosing not to go for headshots in a shooter! And yet, very little of X & Y's design—which always keeps you moving forward, always seeing and doing new things—suggests that staying in a few patches of grass for hours at a time, farming enemies for experience points, is something Game Freak did not intend.
In my 33 hours playing through the main game, I spent maybe an hour or two, tops, grinding. Really, most of that time was me trying to see all the Pokemon available in new areas for my Pokedex, not an active attempt to grind. But not spending an extended period of time grinding and becoming more powerful meant I stayed in a sweet spot where I couldn't just roll through my enemies by finding their weaknesses. Some battles, particularly those toward the end of the game, were too close for comfort.
So my advice is: do battle everyone you come across, don't run away from any random encounters, don't use items like repel—battle as much as you can, basically, just don't go out of your way to level your Pokemon up more than what is normally unavoidable. If done right, the game should provide an occasional challenge.
The systems and mechanics that give life to our favorite little critters are actually surprisingly complex...but the main game does a crap job of showing you that's the case. The bulk of what you need to know when playing against AI is what the different weaknesses are—knowledge of strategy beyond that isn't required.
That's not the case when you play against other people online. People are clever. People use strategy. People will do their best to win—and this means reading up on abilities, natures, breeding, EVs, IVs, items, builds and team composition. It's much harder to simply spam a Pokemon's weakness when a trainer anticipates that you'll try to do exactly that.
Now, I know that playing online can sometimes be an awful experience, and the idea of a JRPG with an online experience is also kind of weird. But not only is Pokemon a far cry from playing a shooter on Xbox Live, the online features in X & Y are so robust, accessible and integral to the experience that, if you choose to not go online despite having the ability to do so, you're straight up playing the game wrong. Hell, at at that point you might as well play an older iteration of the franchise that doesn't have all the wonderful online features that X & Y do.
So, if you can, play against other people as you go along—there are ranked and unranked battles; feel out what works best for you. And if you can't go online, playing offline does mean you get the core Pokemon experience, but not the full, modern Pokemon experience.
Do A Nuzlocke Run
You know of permadeath runs—playthroughs of games that require you to stop going forward once you die? Pokemon has something like that, though it's not built-in to the game. It's called 'Nuzlocke,' and it's a set of rules that someone came up with back in Pokemon Ruby and Sapphire that make the Pokemon games makes things significantly harder. Since then, veterans have continued to use Nuzlocke—and you can, too.
There are many variations to it, but these are the rules I use when going through the game:
1. You can only capture and use the first Pokemon you encounter in each new area, and no others. So if the first Pokemon you encounter in route X is an Oddish, you can capture and use that Oddish, but no other Pokemon on route X. On top of that, if the first Pokemon you encounter in a new area faints, you can't catch any Pokemon in that area. Whatever Pokemon you do catch, however, must be nicknamed. No curses, though. Not my rule, just Game Freak's.
2. If a Pokemon in your party faints, that's it. It's 'dead.' You gotta release it. Kind of morbid, but thems the rules!
3. You can't play with traded Pokemon, unless it's a Pokemon an NPC can trade you.
4. No resets.
5. If you black out (as in, if all the Pokemon in your party faint), that's it. The playthrough is done. Game over. You gotta restart if you wanna keep playing.
The idea behind these rules is that they not only keep the game interesting, they also force players to use Pokemon they'd normally never use. And because of the challenge and restrictions, many trainers come to feel that they form stronger bonds with their Pokemon—which is pretty neat!
Traditionally, people who do Nuzlocke runs sometimes also do comics documenting the experience, as the original Nuzlocker did—you can check some of 'em out here.
Here are some variations/additional rules you can add to Nuzlocke, courtesy of Bulbapedia:
Starter Pokémon is based off the player's Trainer ID number. If the last number is 1-3 the player starts with a Grass type, 4-6 is Fire type, 7-9 is Water type, 0 is the player's choice.
Not officially enforcing the rules until the player has Poké Balls and can catch Pokémon. For example, the PoochyenaRS/ZigzagoonE that the player has to save Professor Birch from is not counted as the first encounter on the route, and not counting any other encounters as such until they can catch. Likewise, in the games where the rival battle is immediately after getting the starter Pokémon, the "any that faint must be released" rule is not enforced at that time.
Going to options and making the battle style "set", leaving the player unable to switch out.
Banning the use of Pokémon Centers, relying only on Potions and healing items for healing
Limiting Pokémon Center visits to a certain number per town.
Banning the use of held items.
Banning the use of Master Balls.
Rather than releasing the Pokémon, it can be permanently boxed, migrated, or transferred with Poké Transfer should it happen to faint.
The player may not evolve captured Pokémon, but evolved Pokémon may be caught.
No catching/using legendary Pokémon.
If the player runs into a Shiny Pokémon on the incredibly rare chance, the player may still catch it, regardless of whether or not it is the first encounter in the area. It also does not need to be released if it faints.
As another mercy rule, each gym badge acts as a checkpoint. If the player gets a game over, they can start from when they got their previous gym badge.
If the player has no Pokémon that can use a certain field move that is required to continue through any given point of the game, they may catch another Pokémon that can learn said field move. However, it cannot be used in battle for any reason, and must be released, permanently boxed, or migrated as soon as the player gets another Pokémon that can use said field move.
Modifying the "first encounter only" rule for the Safari Zone, sometimes allowing one encounter for each area, or until they catch one Pokémon in the entire area, and vice versa.
Banning the use of Poké Marts.
Setting a level limit based on the next Gym Leader's/Champion's highest leveled Pokémon. Any team members that surpass that limit before taking on the Gym Leader or Elite Four must be released.
Most of these are general Pokemon things, though. Let's add X & Y-specific stipulations, shall we? Here's one.
A Nuzlocke run in X & Y MUST require players to max out a Pokemon's friendship in Pokemon Amie. This is something that should take maybe 30 minutes tops, and since it's a mode that requires you to pet, play with and feed your Pokemon, chances that you'll care about the Pokemon are even higher. Excellent. This bond means that if that Pokemon ever faints/'dies', it'll hurt even more.
And here's an optional variation, let's call it the Wonder Run: instead of playing with whatever Pokemon you first encounter in a new area, catch six Pokemon. Any Pokemon will do. Then go into Wonder Trade, which is a new online feature that lets you get a random Pokemon in exchange for one of your own, and trade these six Pokemon away. Whatever you get in return, that's your team. From there, you can proceed as if it's a Nuzlocke Run.
Do Other Types of Runs
Mono-type run: Pick a type—fire, water, grass, what have you—and go forward with a team of only that type. You can pretend you're a gym leader if you'd like.
Solo-run: You get one Pokemon, and one Pokemon only. Add additional Nuzlocke rules, if you'd like.
Community run: Your friends or strangers pick your team, and the moves to go along with every Pokemon. You have to go with it, regardless of what team or moves you end up with...but just to balance things out, at least one of these moves has to be an attack move, ha.
Explore The Post-Game
Now, I won't spoil what comes after you beat the main game...but I will say a variety of new areas open up, as well as challengers who put up a good fight. You also have the option of playing against souped-up versions of previous opponents, like your rivals. It's still not the same as playing against a person that knows what they're doing, but still. It's something.
Catch 'Em All
The tagline for the franchise is no laughing matter. There are more than 700 Pokemon now, and getting a hold of all of them is hard. Give this challenge a try, if you dare—especially if you don't care about the battling in Pokemon. You can think of it a bit like trying to get a full set of furniture in Animal Crossing, only there are hundreds of pieces to collect.
Pokemon has never been a particularly challenging game—and while usually that's worked against the franchise, X & Y is the first instance where the lack of difficulty isn't particularly bothersome for everyone. Still, breezing through a game isn't everyone's cup of tea, and I'd hate for you to pass on one of the 3DS' best experiences because of the lack of difficulty. So, hopefully these tips help—but surely they're not the only options you have to keep things interesting in X & Y. Feel free to share any advice or playstyles you've adopted to make X & Y challenging in the comments!