In a change from the traditional Smash Bros. formula, our generic Pokémon Trainer doesn't get involved with the fighting directly. Instead he sends out his captured critters to do the dirty work for him, that way keeping his attire in perfect condition so that he doesn't have to wash for a week - maybe?
A trio of Pokémon at this disposal doesn't mean three lots of energy, though. Instead, their life is combined. Balancing the abilities of your Pokémon is critical, we'd imagine, especially timing when to bring one in for a rest and sending another out.