A Pokémon Legends: Arceus leak claims the game will have seventeen Hisuian forms for existing Pokémon and that seven brand-new Pokémon will be added in total. Pokémon Legends: Arceus is set in the Hisui region, which is an ancient version of the Sinnoh region. The new setting takes place in a time before humans had built cities and villages throughout Sinnoh's countryside.
Pokémon Legends: Arceus is introducing regional Hisuian forms to the series, and they're one of the semi-open-world game's main selling points. Regional forms are variants of existing Pokémon that evolved differently in-universe due to living in a different habitat than their counterparts. The most recent Hisuian forms revealed were Hisuian Zorua and Zoroark, which are Normal/Ghost-type Pokémon. Compared to the original Dark-types' origin stories, Hisuian Zorua and Zoroark's are much darker in Pokémon Legends: Arceus than in Black and White, as they apparently died out in the colder climate of the Hisui region and have been reborn as vengeful spirits of the dead.
New information declares there are still more Pokémon Legends: Arceus Hisuian forms still to be announced. Pokémon leaker Eclipse said Pokémon Legends: Arceus will feature seventeen Hisuian forms in total on Twitter. The ones officially revealed by The Pokémon Company so far have been Hisuian Braviary, Growlithe, Zorua, and Zoroark. While seventeen is a reasonable figure, it should be treated as a rumor for now. Eclipse also hinted information about these new Hisuian forms will be revealed soon, which follows given the game's January release date.
Eclipse also asserts that Pokémon Legends: Arceus will feature seven all-new Pokémon. If true, this could mean there are at least four left to be shown, as Wyrdeer, Basculegion, and Kleavor have already been revealed in trailers. These are all regional evolutions for existing Pokémon, with Wyrdeer being a majestic evolution of Stantler, Basculegion spawning from Basculin, and Bug/Rock-type Kleavor evolving from Scyther. However, it's unclear whether Eclipse considers these regional evolutions as new Pokémon or if they're counted as Hisuian variants.
The Pokémon Company has gradually been revealing new information about Pokémon Legends: Arceus and Pokémon Brilliant Diamond and Shining Pearl at the same time. The Sinnoh remakes are releasing much sooner than Legends: Arceus, so there will likely be a blowout of Pokémon news later in November. One way to hype the return to Sinnoh would be information about more Hisuian forms, such as the strange Pokémon Legends: Arceus Hisuian Mewtwo rumors that have circulated the internet. There's a lot of potential for Hisuian forms of existing Pokémon to surprise players, and it will be interesting to see which ones could be unveiled next.
Pokémon Legends: Arceus will be available for Nintendo Switch on January 28, 2022.
Source: Eclipse/Twitter