Formerly called Dream World Abilities, Hidden Abilities add another twist to Pokemon. It’s not another game mechanic, but a new feature. But what are Hidden Abilities? They are abilities that differ from a Pokemon’s normal ability. For example, Snivy’s Hidden Ability is Contrary, a new Ability introduced in Generation V which reverses the effects of stat changes. For example, if Snivy is hit by a move like Growl, which lowers Attack, it would now raise its Attack. However, to get this unique brand of Snivy, you would have to be lucky enough to encounter it in the Dream World, and befriend it, of course. The Pokemon can also inherit different Abilities if it evolves. Its evolution may have different Abilities, but it does not happen too often. The Hidden Ability may either be helpful or harmful, depending on the Pokemon. I’ve already given an example: Snivy’s Contrary, which passes on to Servine and Serperior, will prevent against stat-changing moves. An example of a harmful Hidden Ability is Klutz, which prevents the Pokemon from using all hold items that do not deal with experience (EXP Share, Macho Brace, etc.).
The TV in the game which broadcasts the show “What’s That?” says that a Pokemon with Klutz could even hold an Iron Ball without being weighed down. However, Hidden Abilities may not be able to be passed on by breeding, since certain Pokemon found in the Dream World are males. If you’re knowledgeable on breeding, you would know that only female Pokemon can pass their Ability (in this case, Hidden Ability) to their offspring. Also, Pokemon that are genderless, such as Porygon-Z, cannot breed. A comprehensive list of Pokemon with their Hidden Abilites, as well as their availability as females can be found in Serebii. The most Pokemon that are coveted are starters, but as of now, their Abilities cannot be passed down. Therefore, EV training at level 10 should be sufficient, even though the nature may be incorrect. Currently, Johto starters are the only ones that are not available through the Dream World, and countries outside of Japan are still waiting to get more kinds of Pokemon.
For example, in Japan, some exclusive events allowed you to get ones with exceptional Hidden Abilities, such as Togekiss with the Ability Super Luck. It was released only as male, though, and cannot pass on its Hidden Ability. The most important uses for Dream World Pokemon would be in competitive battling, because there is no telling what to expect now that most Pokemon have alternate abilities. And, just like Signature moves, it adds originality. It isn’t too hard to think of a simple battle strategy or move set with these Pokemon, it is just the challenge of getting them which makes them rare and valued.