Maybe you missed that it's Teddiursa who evolves into Ursaluna. It looks to be a split evolution a la Slowbro/Slowking.
EDIT: Outdated intel.
See below.
I haven't spoiled the boss fights for myself, but based on the moves we know are in the game it shouldn't be hard to identify the frontrunners. I will omit the new forms of Dialga and Palkia because they are obviously endgame monsters, they are hardly different from the standard forms, and they will be surefire Ubers once they enter the main series. I will also omit Enamorus because she's probably postgame and I've shilled her enough already.
- Hisuian Goodra—It's already a pseudo, and it's only been improved by its new form.
- Ursaluna—Even without Guts, base 140 Atk is nothing to sneeze at.
- Kleavor—Same speed as Overqwil and the new Samurott, but it's stronger and benefitting from buffed X-Scissor.
- Hisuian Arcanine—This guy's probably the reason why Head Smash is in the game. High BST as always.
- Sneasler—Basically Weavile but with stronger STAB moves across the board. You just know they're giving this thing Close Combat.
The last slot is a toss-up.
I want to say
Overqwil because it looks stronger than the new Samurott by stats, but we don't know that it gets a good Dark move.
I also want to recommend
Hisuian Zoroark because it's a faster version of the new Typhlosion, but I'd first need to be sure that it learns Tri Attack.
Finally,
Hisuian Lilligant will be good someday, but it's not that strong without Hustle. It's already better than the new Decidueye.
As with many hyper-restricted team requests (
cough 6-CAP
cough), a 6-Hisui team may need to settle for something less than optimal. I suppose #6 should be whichever one of the aforementioned three gets what it wants. They potentially outcompete the starters, but they each need a little something extra to boost them above the rest of the roster. Keep an ear out for news on them.