The Water-type fish Pokémon Basculin was introduced in Generation V and has two appearances. Some Basculin have red stripes and spiky fins, while others are blue-striped with rounded fins. The species as a whole is considered one of the meanest Pokémon in the games, earning the nickname "thug of the lake" in Pokémon Ultra Moon's Pokédex entry for blue-striped Basculin. With the exception of the hardy and strong-willed Corphish and its evolution Crawdaunt, other Pokémon abandon waters where Basculin dwell because they are so vicious, according to Ultra Moon's entry for red-striped Basculin. These fish will even terrorize each other, despite occasionally swimming together in schools.
Perhaps it is no surprise that such a mean-spirited Pokémon evolves under sad circumstances. Newly discovered in Pokémon Legends: Arceus, Basculin evolves into the Water/Ghost-type Basculegion when the souls of Basculin who died trying to swim upstream possess another Basculin. On the surface, this evolution may sound like Basculin is receiving strength from those that came before and is fighting in their memory. However, a closer look at Basculegion's namesake and its nature reveal a potential dark connection, adding to the mild horror element seen so far in Legends with the new forms of the spiteful Zorua and Zoroark.
A legion is a unit, commonly referring to the numbers of an army or a large gathering of people. Basculegion is a collective of numerous Basculin, so the reasoning behind the name seems simple enough. However, because of the nature of Basculin's evolution, a different sort of legion also comes to mind.
A legion is also a demon named in the New Testament of the Christian Bible, referenced in the fifth chapter of the Gospel of Mark, verses one through 20. The story in this chapter tells of a Genesarit demoniac, someone possessed by demons who lives in a cave away from the main settlement. He meets Jesus, who demands the demon within identify itself. The demon responds that its name is Legion and that "we are many." Before leaving the man, it begs to enter into a herd of pigs instead. Jesus allows it, and then the possessed herd of pigs stampede into water where they drown.
The dead Basculin shares enough similarities with the demon of these Bible verses to think maybe the naming of its evolution as Basculegion is not simply a reference to numbers. Basculin is a violent, vicious Pokémon that, when they die in the water, can return to haunt this world as ghosts, a spiritual form. They possess a living Basculin from their school and thus evolve into Basculegion, gaining power from numbers. Basculegion does not grow tired from swimming, and the ghosts of the dead Basculin can seemingly attack of their own accord. As a result, Basculin becomes as dangerous and unfriendly in death as they were in life.
The perceived parallels within Basculegion's naming is an interesting link for one of Pokémon's meanest creatures. So far Basculegion has only been shown in the red-striped form. Perhaps an evolution specific to blue-striped Basculin will be revealed, one that leads to a more redeeming end for the "thug of the lake."