Basculin is a green aquatic Pokémon that comes in three forms. The bodies of both the Red- and Blue-Striped Forms are the same. They have a green, ovoid body, tapering off in the rear to a trapezoidal tail fin. A thick black stripe covers the top of their body from mouth to tail and a white, dorsal fin with four protrusions resembling spikes. Their lower jaw juts ahead of their upper jaw, with a small indent near the edges of their mouth. Both forms have three black dots on both sides of their body, behind their pectoral fins.
The main difference between the three forms of Basculin is the color of the stripe that separates the black and green on their body. All forms of Basculin have fins in the same places, with one on top of their body ahead of the tail fin, one below the body ahead of the tail fin, and two side fins. The Red-Striped Form has jagged fins that resemble tridents, whereas the Blue-Striped Form has smooth fins all around. The Red-Striped Form has circular, red eyes, while the Blue-Striped Form has narrower, blue eyes.
Red- and Blue-Striped Basculin are extremely hostile, especially towards their opposite form. They generally start fighting each other on sight for territory. However, on rare occasions, one form may swim with the other's school. Basculin is full of vitality and reproduces quickly. When a school of Basculin appears in a lake, Pokémon other than Corphish and Crawdaunt flee. It competes with Carvanha for food.
Basculin has often been referred to as "the thug of the lake" or "Thug of the River", and uses its jaws, which are strong enough to leave bite marks in iron sheets, to devour everything in its way. However, despite their fierce reputation, Basculin become prey to stronger organisms, such as Bombirdier and Dondozo. Basculin were once also consumed by humans, and were considered very delicious. The meat of Blue-Striped Basculin has an inoffensive, light flavor, while the meat of Red-Striped Basculin is fattier, and was more popular with the youth. Basculin is a popular Pokémon with anglers due to its resistance. Many people release Basculin into lakes illegally, causing its population to grow abundant.
Basculin has three separate forms: Red-Striped Form, Blue-Striped Form, and White-Striped Form, the last of which is sometimes considered a regional form.
In Hisui and Kitakami, White-Striped Basculin has a similar appearance to the other two forms of Basculin. Despite its descriptor, the stripes above its eyes are actually a very pale shade of light blue, as are its irises. Its pectoral fins are smooth like Blue-Striped Basculin, but larger. Its dorsal fins are spiky and it has wide eyes, like Red-Striped Basculin. Its lower jaw is smaller than the jaws of either Red- or Blue-Striped Basculin, and both its lower and upper jaws have beak-like protrusions at the front.
Unlike the other two forms, White-Striped Basculin are known to be gentle, with an ecology different enough from other Basculin to spawn recent theories of it being a separate species. White-Striped Basculin are known to share food with each other unlike their two counterparts. They are known to travel upstream; the journey is often perilous for the species, and many of them don't survive. As a result, the souls of the deceased White-Striped Basculin are often left behind in the waters of Hisui. However, when an injured White-Striped Basculin survives, it can unite with the souls in order to achieve the unique evolution into Basculegion.
White-Striped Basculin can evolve into Basculegion. Neither Red-Striped Basculin nor Blue-Striped Basculin can evolve.
Basculin has three non-interchangeable forms: Red-Striped Form, Blue-Striped Form, and White-Striped Form. White-Striped Basculin is also considered to be a Hisuian Form in some contexts (such as Pokémon HOME and its Pokémon Legends: Arceus Pokédex entry).
Bred Basculin are the same form as their mother, or the same form as the Basculin parent if bred with Ditto. This includes White-Striped Basculin (who is not treated as a regional form for breeding, which would require it to hold an Everstone to pass down its form). If Basculegion is the mother or is bred with Ditto, the offspring will be White-Striped Basculin.
Only Red-Striped Basculin can have the Ability Reckless and may hold a Deep Sea Tooth when encountered in the wild.
Blue-Striped Basculin initially had access to another set of Abilities in Pokémon Black and White, which is the same as Red-Striped Basculin's (having Reckless instead of Rock Head). However, a Blue-Striped Basculin available in an in-game trade in Pokémon White has the Ability Rock Head.
White-Striped Basculin evolves into Basculegion after losing at least 294 HP from recoil damage. This can be spread across multiple battles and is not affected by the use of recovery items. Fainting will reset progress. In Pokémon Scarlet and Violet, White-Striped Basculin must level up after losing at least 294 HP from recoil damage in order to evolve.
White-Striped Basculin doesn't follow the standard naming convention for regional forms. All other regional forms are named after the region they originate in, with region name preceding species name, such as "Hisuian Sneasel" or "Alolan Meowth".
Pokémon Scarlet and Violet does not internally classify White-Striped Basculin as a regional form. Therefore, while breeding, a White-Striped Basculin or Basculegion parent is not required to hold an Everstone for the offspring to hatch into White-Striped Basculin.
In addition to Hisui, White-Striped Basculin is found in the wild in Kitakami and is (along with Basculegion) part of its regional Pokédex, unlike all other regional forms, which are only naturally found in a single region.
Basculin is based on a bass, most likely the largemouth bass due to its greenish color, pattern of horizontal splotches, and vigorous resistance when being fished. It is likely also inspired by the piranha, which has historically been viewed as violent. Its Red-Striped and Blue-Striped variations that are hostile to each other are similar to Siamese fighting fish, which come in a variety of colors (including red and blue) and are extremely aggressive and territorial to others. It could also be compared to street gangs, where groups of affiliated people often fight rival groups over their own territory.
According to interviews with Ken Sugimori in Nintendo Dream Vol. 205, Basculin was created late in development when they realized there were few new "standard" fishlike Pokémon in Unova, the only others being Alomomola, Stunfisk, Frillish, and Jellicent. It was given two forms to make up for the small number of fish in the region, and it was also based on a bass since there are wild bass in New York.
While Basculin's White-Striped Form may likewise be inspired by a bass, its design is also reminiscent of the salmon or the related itou (Sakhalin taimen), due to its behavior and the shape of its mouth resembling the kypes that develop in male salmon.
The selection of colored forms being red, white, and blue may reference the national flag of the USA, where Unova, the region Basculin was first introduced, is based.
Basculin may be a combination of bass and masculine.