Castform

Castform (Japanese: ポワルン Powarun) is a -type Pokémon introduced in Generation III. Its body changes with the weather; sunny, rain, hail, and its normal form.

Physiology
Castform is one of few human-made "artificial" Pokémon. It was created on purpose by the researchers of the Weather Institute in the Hoenn region as an experiment in weather forecast and manipulation. Castform's main color is a cloudy white. Around its eyes is white and in the shape of a mask. Castform is able to change forms according to the weather. It has a rain, sun and snow form. The rest of its body is a plain gray color.

Special abilities
Castform's cellular structure is closely related to the weather conditions, meaning that Castform can both affect and be affected by the weather. Depending on the current weather and climate, Castform's emotions and even body are altered. In this way, Castform tries to adapt itself to multiple environments.

This extraordinary trait is referenced in the video games through the Forecast ability, which changes Castform's type and appearance depending on the weather. In weather not particularly extreme, Castform's type is normal and its appearance is as described above.
 * In intense sunlight (induced by the Sunny Day move or the Drought ability) Castform becomes a type. Its head turns red, its eye markings become yellow and its head is enclosed in a translucent orange orb adorned with smaller orange orbs, giving the impression of a stylized sun. Its lower body becomes larger and paler, like a puffy white cloud.
 * In torrential rain (caused by the Rain Dance move or the Drizzle ability) Castform becomes a -type. Its head turns dark blue, its eye markings become a lighter blue and its head is enclosed in a blue raindrop shaped structure. Its lower body grows and darkens, reminiscent of a storm cloud.
 * In hail fall (brought about by the Hail move or the ability Snow Warning) Castform changes into an type. Its head turns violet, its eye markings become a lighter violet and its head is enclosed in a complex emerald-colored structure that is meant to represent a snow cloud.

Evolution
Castform does not evolve.

Anime
Castform was featured in episode Unfair-Weather Friends, in which operatives of both Team Aqua and Team Magma attacked the Weather Institute trying to steal data on Kyogre or Groudon, as well as weather-changing technology. This also happens in Generation III games RSE, when you go to the institute.

Trivia

 * Not including Mega Evolution and Alolan variations, Castform is the first Pokémon in the Pokédex order to have alternate forms.

Trivia
Castform