Some sources have exploited cheats and secrets in Pokémon X and Y generation which reveals hidden ways to unlock easy rare candies, PP ups, Poke Miles, full heal and infinite heart scales.
Easy Rare Candies
Rare candies aren't sold from any mart except via Poke Miles purchase and if you want to get faster level up using these candies, follow the steps to boost the new currency.
1. Gain Poke Miles via Street Pass or Wonder Trade.
2. Trade Pokémons via Wonder Trade sequence and accumulate Poke Miles easily.
3. Once you have enough Poke Miles, head over to Lumiose City then enter the Pokémon Centre.
4. Talk to the old man in white suit to purchase rare candies and PP ups.
5. Alternatively, use your Poke Miles at the Global Link Mileage to buy exclusive items with 50 per cent discount.
Heal for Free
Battling over Wi-Fi in Pokémon X and Y will let you restore HP and PP for free as if visiting a Pokémon Centre. Start a battle, wait for your partner to accept then finish the battle. Another way is battle with a friend then decided to quit the battle, once your friend accepted it, HP and PP will be restored.
Three Legendary Birds
If you want to capture Articuno, Moltres and Zapdos found in Pokémon Red and Blue, defeat Kalos region's Elite 4. Check the Coastal Kalos Pokédex then track the location shown to you by walking instead of flying. If the legendary Pokémon flees on you, track and repeat few more times till it reaches Sea Spirit's Den where you should catch it.
Legendary bird matches your starting Pokémon depending who you've chosen beforehand:
Legendary Bird Pokémon
Infinite Heart Scales
Heart scales are item you can use to teach Pokémon moves you forgot or have never learned at the Move Relearner NPC in Dendemille Town. Use the Old Rod from Ambrette Town in the Aquarium by the Magikarp statue and TM46 Thief move from Cassius's house in Camphrier Town.
Go to Route 8 - Muraille Coast then battle Luvdiscs using the Old Rod. Use the Thief move to get Heart Scales from Luvdiscs. There is a good 50 per cent chance that you may steal a Heart Scale and this event is repetitive.