True. If we take the megas available into consideration, I could see the following pokemon participating:
1) Kangaskhan
2) Mewtwo (as final boss)
3) Scizor
4) Heracross (otherwise Sheep doesn't buy it)
5) Blaziken (confirmed)
6) Aggron (similar to Jack)
7) Medicham (almost confirmed)
8) Lucario (confirmed)
9) Abomasnow (why not?)
10) Swampert (what about that new mega?)
11) Lopunny (almost confirmed)
12) Gallade (please please please)
But 12 characters are not nearly enough. So I nominate:
Ursaring, Regigigas, Infernape, Emboar, Machamp (confirmed), Hitmonlee, Hitmonchan, Pangoro, Poliwrath, Toxicroak, Chestnaught,
Greninja, Hawlucha, Nidoking, Drapion, Electivire, Eelektross, Sandslash, Krookodile, Golurk, Armaldo, Barbaracle, Rhydon,
Bearctic, Weavile, Genesect, Druddigon, Zoroark, Bisharp.