While Sapphire and Ruby were in development, Mawile was initially supposed to be a Dark-Type instead of a Steel-Type. But a programmer made a mistake and accidentally listed the Pokemon as Steel and the error went unnoticed. But once GameFreak did notice the mistake, it was too late; the two games had been released to the public. However, some feedback of the games told GameFreak that Mawile being a Steel-Type was actually favored among many players. Thus, Mawile is forever a Steel-Type.