It is not always clear who among the Basculin survived the journey upstream; perhaps, like Wishiwashi, they all merged into one. Basculegion are most securely attested in Hisui, but stories abound of them anywhere migratory Basculin come into contact with expanding civilizations.
Basculegion are said to rule the ocean with such might that even their notoriously aggressive prevolutions swim away from their gaze, fearful of losing their individuality within the School of the Dead. They have a special enmity for Ursaluna, who are known to eat Basculin; in areas where they are absent, Bewear, Pangoro, and Beartic are also known to be targeted by their attacks, for a leaping ghost can easily wave crash those fishing by the shore.
It is difficult to discern where fact ends and fiction begins with the Basculegion: could a half-transparent pokemon really have ever carried a rider? Did pirates consider them such a horrifying omen that they refused to set sail when one was sighted in nearby waters? Sadly, one can not be certain of these tales, for few Basculegion remain these days to confirm or refute them.
It is one thing to take revenge on bear pokemon; a far more difficult task to do so on humanity. Some pokemon, such as Grimer and Pidove, have flourished because of human changes to the environment, but industrial runoff kills far more Basculin than predators and is not nearly so easily avenged. Ghost pokemon do not, can not die out, and the old ones, in protest, have refused to move on. But it is a mighty challenge for any Basculin today to assemble enough spirits to evolve, for they are no longer dying the correct way.