Pokémon X and Y introduced the Fairy type to the Pokémon type system.
Fairy was the first new Pokémon type added since the Dark and Steel types appeared in Pokémon Gold and Silver. Its introduction changed type matchups across the series and gave several older Pokémon, including Clefairy and Jigglypuff, a new or additional type.
Fairy-type attacks are super effective against Dragon, Fighting, and Dark Pokémon. Fairy Pokémon are weak to Poison and Steel attacks, while Fairy itself is immune to Dragon-type attacks. These matchups were designed in part to rebalance the powerful Dragon type.
Pokémon X and Y were released worldwide for Nintendo 3DS in October 2013. They also introduced Mega Evolution, character customization, and fully polygonal 3D presentation. The games added 72 new Pokémon species, but Fairy was the major type-system addition that affected both new and existing Pokémon.