Which type debuted in the Pokémon X and Y video games?

The Fairy type debuted in the Pokémon X and Y video games.

Released in 2013, X and Y introduced Fairy as the first new Pokémon type since the addition of Dark and Steel in Pokémon Gold and Silver. The new type was designed partly to rebalance battles, especially by giving Dragon-type Pokémon a clear weakness.

Fairy-type Pokémon and moves became important parts of the sixth-generation battle system. Fairy attacks are super effective against Dragon, Dark, and Fighting Pokémon, while Fairy Pokémon are resistant to several traditionally powerful types. The games also changed the type classifications of some existing Pokémon, including Clefairy and Jigglypuff.

Sylveon, an Eevee evolution, was one of the best-known early Fairy-type Pokémon. Its introduction helped demonstrate that the new type was not limited to newly created species. Fairy remained part of the main battle system in later generations, although its move interactions and individual Pokémon matchups continued to vary.