While the exact codes change as Datel updates the server, below are the classic, most reliable codes trainers look for in Pokémon X and Y . (Note: These are typically applied to the cartridge via PowerSaves, not typed in-game).
Pokémon XY stores values in the save file and RAM. Cheat codes work by overwriting memory addresses in real time: pokemon xy cheat code
However, I can give you a that explains how cheat codes generally work in Pokémon XY , the risks involved, and safer alternatives. While the exact codes change as Datel updates
If you want total control, PKHeX is superior to any pre-made "code." It is a save editor that runs on your computer. below are the classic