Koratta

Rattata is a small, quadrupedal rodent Pokémon. It has purple fur with a cream-colored face, paws, and underbelly. It has narrow eyes containing white sclera and pupil with red irises, rounded ears with cream-colored insides, and a single whisker on each cheek. Its long tail is tightly curled at the end. Its most notable feature is its large teeth. Like most rodents, its teeth grow continuously throughout its life and must be worn down by gnawing. This also ensures that Rattata is not awoken by the sound of its grinding teeth while sleeping. Females will have shorter whiskers.

Rattata can live wherever it can find food, which it searches for most of the day. Thanks to its sharp fangs, it is able to chew on nearly anything. When it is threatened, Rattata can deliver a powerful bite. Rattata constantly keep their ears up and will immediately scurry away from the slightest sound. Furret is the natural predator of Rattata. Its hardiness lets it live in many environments, although it mainly lives on plains and savannas. Because it reproduces so quickly, a pair of Rattata can quickly colonize an area. As shown in Pokémon Sleep, Rattata is known to sleep sometimes with a log in its mouth.

Forms
Rattata has a regional form: Alolan Rattata.

Due to territory disputes with the Yungoos line, Rattata has taken on a new appearance. It has dark gray fur and grayish-purple ear insides. There are two tufts of fur on each ear and near the tip of its tail. Its long, thin whiskers are also replaced by shorter, thicker tufts of fur. The line where its cream underbelly meets its gray fur is ragged instead of smooth. Unlike its Kantonian form, it often stands on its hind legs, giving it a more bipedal appearance.

Rattata are non-native to Alola and arrived in cargo ships. The Rattata population in Alola was booming until Yungoos and Gumshoos were imported as a control measure. In order to avoid these new predators, Rattata altered its habits. It moved to more urban areas, became nocturnal, and formed large nests led by Raticate. Each nest has an Alolan Raticate serving as their boss.

Alolan Rattata searches out fresh food by smell and ignores anything spoiled. The whiskers provide Alolan Rattata with a keen sense of smell, allowing it to find hidden food instantly. Humans are known to use Alolan Rattata when they go shopping for fresh food.

Alolan Rattata are more active when the sun sets. Alolan Rattata will search for food in order to give to their boss. It has even been known to sneak into people's homes to find food. They use their whiskers to locate the food in said homes. There have been massive outbreak in Alola due to this. As a result, Alola Rattata has become an issue of public concern for humans.

Evolution
Rattata evolves into .
Alolan Rattata evolves into Alolan Raticate.

(Source: Bulbapedia)