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Masuda method - Bulbapedia, the community-driven Pokémon encyclopedia →

"Reaction and purpose

From Generation IV onwards, trading with games from other countries became easier due to the Nintendo DS’s ability to communicate through Nintendo Wi-Fi Connection. The Masuda method was likely coded as incentive for players to use the GTS’s international trading services.
Though the odds of obtaining a Shiny Pokémon are still fairly low, the chances have now been increased significantly enough that players have touted it as a more reliable method than the Poké Radar. The Masuda method is even more appealing, since it allows players to customize their team further, with specific Egg moves, Natures and IVs that would be either unavailable or harder to obtain.