Why does my Basculin have Rock Head?

Question

The abilities Basculin is supposed to have is Adaptability, Reckless, and Mold Breaker(Hidden ability). So why does my Basculin have rock-head?

EDIT: I found the basculin in some rippling water

Answer 1

Reckless, Adaptability and Mold Breaker are indeed the "normal" abilities for both Red- and Blue-Striped Basculin in Gen 5. However, there is a limited number of ways to get a Blue-Striped Basculin with Rock Head in Gen 5. One of these scenarios must apply:

1. In White, the Blue-Striped Basculin received in a trade in Driftveil City has Rock Head. (In Black, you receive a Red-Striped Basculin with Reckless.)
2. In Black/White 2, wild non-HA Blue-Striped Basculin appear with Rock Head or Adaptability, and never Reckless. (This does not apply when breeding Blue-Striped Basculin.) If you found Basculin in rippling water, then this situation must apply.

As of Gen 6, Rock Head is formally an ability for Blue-Striped Basculin instead of Reckless. If a Blue-Striped Basculin with Reckless is transferred to Gen 6/7, its ability will become Rock Head.

Source

Comments

If Rock Head, Adaptability, and Mold Breaker are Blue Striped Basculin's possible abilities, how/why is it possible to get Reckless Blue Striped Basculin

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I don't know implementation details, but clearly an error was made with Blue-Striped Basculin's ability and the game's ability slot system is not strongly enforced.

Answer 2

In White, the in-game traded Basculin has the ability Rock Head.
>...however, the Blue-Striped Basculin that can be obtained via in-game trade in White has the Ability Rock Head -Bulbapedia

Comments

Thanks, I thought it was an awesome glitch though. :)

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Does anyone know if this Basculin keeps it’s ability when transferred to Gen 6?

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Yes, Rock Head stays.
(In future, if you have a follow-up question, you should make a new thread for it. It's much more likely to get an answer and it's better for organisation.)

E: answer above is incomplete, will write a better one soon