Castform (Japanese: ポワルンPowarun) is a Normal-typePokémon introduced in Generation III that's name is a combination of forecast and transform: its body changes with the weather; sunny, rain, hail, and its normal form.
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.
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 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 Fire 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 Water-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 Ice 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.