Lets take a look at all the new Pokemon and their shinies:
And some more details here:
In this Pokemon Legends: Arceus New Pokemon and Forms Guide we'll go over all the new Pokemon you can expect to see in the Hisui region.
techraptor.net
So, ALL the starters get new final forms. I'll admit, I'm kind of leaning towards Samurott, now. But fire's so useful in these games early on, and I feel like Typhlosion will look a lot better when we get to see the flames around him, and fire/ghost is a interesting combination. All of them get interesting combinations, I kind of like all three well enough. All three are tempting choices. And it looks like all their shinies are based on their original colors...so that probably means something interesting for regular-Typhosion's flames.
Arcanine is GREAT. He looks really cool.
And both versions of Basculegion look really good. Though, I prefer the female versions shiny, I think.
Overqwil is a great name. And it's about time Qwilfish got a evolution. And a neat looking one to boot.
Zorua, Zoroark, and Braviary all get great shinies.
Getting a new member of the Forces of Nature is a odd choice. Especially since those guys are from Gen5 not Gen4.
Now...about those new Legendary forms....I don't like 'em. They look so weird to me. I guess that makes them stand out, though. Apparently, they get these forms from their Adamant and Lustrous Orbs, like Giratina's Griseous Orb. But with Dialga's lack of legs, and Palkia's lack of arms, it makes me wonder if they can combine down the road.
Now, it's odd that Arceus doesn't have a new form, but I guess he's getting a Legend Plate that can give Arceus every typing all at once...so I have to wonder if we're going to get a Day 1 patch that'll put in a new form for Arceus, too. Which would explain why it isn't in this datamine, since the patch wouldn't have gotten leaked, too.
Although, if the rumors are true and there is no breeding...I'm not sure how I'm going to get the other two starters. Might have to wait until Pokemon Home updates and do a couple of playthroughs just to get the other two starters.