Answer 1

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

Comments

my answer was out classed :P

Answer 2

Hidden ability is the ability that some pokemons get only from Dream World .For example Bulbasar has the hidden ability Chlorophyll which boosts the Pokémon's Speed in sunshine.Bulbasar can't get this ability.Also there are some moves that pokemon get only from Dream World like Sukern.If you catch it in the DW it will have the move Earth Power.

Hope this help!

Comment if you want more informasions.

Comments

Why did you downvote him?

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Please remove the downvote this was a good answer that you answered 7 mins later and downvoted him we can tell you downvoted as well because it says you gave a downvote and you lost 2 points
Also this applys to uberpwnage once something has a good answer don't answer it again you will not get votes

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When I started typing my answer, there was nothing yet. It was not until i added my answer (which refreshed the page in the process) that i saw you answered Blobyolo. Sorry.

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No I'm ok with that your answer was much better :) but black enplolian answered way after you and then downvoted you because I gave you an upvote - it's sad what he's done

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http://chzpokememes.files.wordpress.com/2011/10/8b2c6181-710f-474f-9816-1b689e7f5bb5.gif

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there i upvoted him back