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The trainer is allowed to fight, therefore potentially expanding everyone's team to 7. They can concede when their Pokemon are knocked out, unless if they choose to add themselves to the fight at any time midbattle by switching in.
Trainers all have the same movepool and are Normal type, with potential for Fighting, Psychic, or various other types by external training methods perhaps. They get an array of held items that Pokemon wouldn't be able to use.
Additionally, this comes with an Ace mechanic, where you select an Ace mon and it's basically a toned down version of Megas/Dynas with form changes(to retain the Mega designs), ability/type changes, and stat minmaxing/bonuses. It's able to unlock its potential in battle and you get options to do tag team attacks with it as the trainer.
But basically imagine boxing your starter and punching your way through the whole game.
