So I don't think anyone has made a list for this yet so thought I would.
Pokemon Seen in the Pokemon ZA Trailer + Extended Look:
Skiddo (Gogoat)
Mareep (Flaaffy & Ampharos + Mega)
Sliggoo (Goomy, Goodra)
Clauncher (Clawitzer)
Furfrou (There is minor background art of at least 1 of the "Cut" Formes as well)
Sandile (Korokorok, Krookodile)
Starters - Totodile, Tepig & Chikorita
Bunnelby (Diggersby)
Fletchling (Talonflame)
Scatterbug (Spewpa, Vivillon)
Pyroar (Litleo)
Lucario
Mega - Kangaskhan, Absol, Sableye, Altaria, Charizard Y, Ampharos, Gyarados, Charizard X, Gardevoir
Eternal Floette - Humourously memed by Pokemon themselves
Zygarde 10%
Budew (Roserade)
Florges (Statue and later team image)
Eevee (Jolteon, Flareon, Vaporeon, Sylveon, Glaceon Umbreon
Patrat
Pikachu (Raichu)
Bellsprout (Weepinbell, Victreebel)
Larvitar
Bagon
Aegislash
Trubbish (Garbodor)
Chandelure
Magikarp (Gyarados)
Swablu (Altaria + Mega)
Swirlix (Slupuff)
Spritzee (Aromatisse)
Hippowdon
Pidgeotto (Pidgeot)
Onix
Dragalge
Dedenne
Inkay
Zygarde Cell
In most instances I've logged the first sighting of a family first - but probably safe to say if a family is shown, all evolutions are probably available.
I'd probably also lean towards all the megas being available as well (which means the other Kanto Starters [Venusaur/Blastoise], Alakazam, Gengar, Pinsir, Aerodactly, Mewtwo [Who already exists within Kalos], Scizor, Heracross, Houndoom, The Hoenn Starters [Sceptile, Blaziken and Swampert], Mawile, Aggron, Medicham, Manectric, Banette, The Lati Twins [Latias/Latios], Garchomp, Abomasnow, Beedrill, Slowbro, Sharpedo, Camerupt, Glalie, Metagross, Rayquaza [This one is the least likely imo], Lopunny, Audino and Diancie) may also show up. The Megas they've shown have been a mix of "Original" and "Hoenn" megas, so will be interesting to see.
I'm interested in how the UI works as well, the "C+"? tags on the Mega's moves might make them act differently to the moves normally when not in Mega as well. Timers for megas makes sense from a "Real Time Battle" format. It doesn't look like using moves speeds up the timer or anything like that so I would assume that most megas just last for 60 seconds or something and then go away. I do wonder how you charge that meter though, or whether it is like Tera and gets recharged when you heal.
Overall I'm interested in the direction LZA has taken, the art style reminds me of New Pokemon Snap (which is probably the best looking game they've done) and I like that the characters have taken on that style of animation. More of that going forwards please!
All I want out of Champions is good PvE content. If its PvP only, it'll just be a pass from me. I've never been one to be mad about the Battle Facilities, but with the steps they have made to make "Competitive" Pokemon easier to produce, it would be nice to be able to use them somewhere. Restricted Sparring back in the SwSh DLC is the last "proper" facility we've had. Just a shame we won't ever see the Minigames again a la Stadium 1/2.