Shellos

Shellos, known as the Sea Slug Pokémon, was introduced in the fourth generation of Pokémon games, beginning with Pokémon Diamond and Pearl. It is a Water-type Pokémon with a unique feature that distinguishes it from many others in the Pokédex: its regional variations. Shellos has two distinct forms, West Sea and East Sea, each featuring different colorations and appearances based on the area in which it is found within the Sinnoh region. This characteristic was inspired by Darwin's studies of species variation, adding a layer of scientific intrigue to its design.

In the mainline Pokémon games, Shellos is not a starter Pokémon nor does it hold a legendary status, but it is an example of the game's exploration of environmental adaptation, a theme that resonates well with the ecological diversity seen in the Sinnoh region. Its regional forms are a precursor to the more expansive regional variant concept seen in later Pokémon generations, such as Alolan and Galarian forms.

Shellos does not evolve into a particularly powerful Pokémon in terms of competitive battling, but its evolution, Gastrodon, gains the additional Ground typing. This gives it an interesting niche in battles with a strong resistance to Electric-type moves, which is uncommon for Water-types. This dual typing and its role in helping trainers understand the concept of environmental influence on Pokémon forms have helped Shellos endure across generations.

While Shellos may not be the most striking in terms of competitive prowess, its role in broadening the Pokémon universe’s understanding of regional diversity and adaptation makes it a memorable creature. Its presence in Sinnoh, a beloved region that was revisited in the Pokémon Brilliant Diamond and Shining Pearl remakes, ensures its continued relevance in the franchise.