In the Hisui region, some Pokémon have received new regional forms that differentiate them from the regions they were originally found in. Not only that, some Pokémon have regional evolutions that can only be obtained in ancient Sinnoh.
Regional forms in Pokémon Legends: Arceus
Battle Cry Pokémon • Type: Psychic/Flying
When Rufflet in the Hisui region evolve, they become Hisuian Braviary. In the winter, this Pokémon flies in from somewhere farther north. It’s larger than the previously discovered form of Braviary and tends to live alone rather than in flocks.
Scout Pokémon • Type: Fire/Rock
This is Growlithe as it appears in the Hisui region. Its Hisuian form has longer, more voluminous fur than the previously discovered form of Growlithe. This soft, heat-retaining fur helps the Pokémon thrive even in the frigid Hisui region. The sharp horn on its head is made of rock, but it breaks easily, so Hisuian Growlithe uses it only when it’ll have the greatest effect.