Generation V introduced Hidden Abilities, providing almost all Pokémon with another Ability. These Abilities are not found on Pokémon found randomly in the wild; only Pokémon obtained under special circumstances have these Abilities. All Pokémon obtained from the Pokémon Global Link, either via the Pokémon Dream World or a promotion, will always have their Hidden Ability, if they have one. Certain event Pokémon may also have their Hidden Ability. In addition, two incidences of Pokémon found in-game, the five Darmanitan in the Resort Desert and the Musharna found every Friday in the Dreamyard, also have their Hidden Ability.
If a female Pokémon has a Hidden Ability and is bred, it has a 60%
chance to give that Ability to each of its children. Hidden Abilities
cannot be passed down from male or genderless Pokémon, or when
breeding with Ditto.
Hidden Abilities On Bulbapedia