Castform

“CASTFORM’s appearance changes with the weather. This POKéMON gained the ability to use the vast power of nature to protect its tiny body.”

— Pokémon Ruby

“CASTFORM borrows the power of nature to transform itself into the guises of the sun, rain clouds, and snow clouds. This POKéMON’s feelings change with the weather.”

— Pokémon Sapphire

“It alters its form depending on the weather. Changes in the climate such as the temperature and humidity appear to affect its cellular structure.”

— Pokémon Emerald