Take what you want with this information. I work in the games art department, designing what we are requested. I’m not gonna say more than that so I don’t run the risk of being fired.
Final Starters:
Rabblaze - Looks very humanoid, and is fire/electric.
Beatonga - A giant monkey who beats on its wooden chest as a drum
Intelleon - Chameleon spy, as the Affleck leak said.
Gigantamax Forms:
Kanto:
Charizard - Looks like it’s X mega form, but will red flames emitting from its mouth instead, but black skin and a deep red belly.
Pikachu and Eevee - Both get G-forms, but the only way to obtain them is when Home releases, and you can send over your partner from LGPE. Both Pikachu and Eevee represent their old-school art.
Gengar - Kind of like it’s mega, it has a red gem in its forehead, but kind of becomes a spider, with 8 legs cover in spikes. I believe it’s max move sets up toxic spikes.
Machamp - A lot of arms, steam emits from its body, kind of like in pokken

Sinnoh:
Infernape - Perhaps the coolest form of all, it resembles a black knight, but you can still see it’s Infernape. Ironically, it fights with a sword and shield. There isn’t a form for Torterra or Empoleon, a sign of remakes? We weren’t told how far ahead yet.
Galar:
I’m only going to tell you guys about the 3 starters, as I have worked very closely on some forms for new Pokémon.
Intelleon (Sobbles final evo) - It’s tail becomes long and pointy, the hands and feet become bigger, and it can grow a cape.
Beatonga (Grookeys final evo) - Goes from obese to a Thin monkey and becomes incredibly more feminine. It still has its rock typing, and can use its hairpiece during its max move as a flute to lure the Pokémon to sleep.
Rabblaze (Scorbunny final evo) - This Pokemon gains eyeware and becomes even more athletic looking, gains chest pieces, and can summon/kick around either an electric or flame ball.