Which Pokémon game introduced Alolan Forms, regional variants with different appearances and types?

Pokémon Sun and Moon introduced Alolan Forms, regional variants of older Pokémon with changed appearances and types.

Released for the Nintendo 3DS in 2016, the games take place in the tropical Alola region. The new forms reflect how familiar Pokémon adapted to Alola’s distinct island environments and ecological conditions.

Examples include Alolan Vulpix, which changes from Fire type to Ice type, and Alolan Raichu, which becomes Electric and Psychic type. Alolan Exeggutor also gained a dramatically longer body and a Grass/Dragon typing.

Regional forms are different from entirely new species: they use the identity of an existing Pokémon while presenting a region-specific variation. The idea later became a recurring feature in Pokémon games, including Galarian Forms in Pokémon Sword and Shield and Hisuian Forms in Pokémon Legends: Arceus.