We might have to get creative for that. In the video games, you're one person with a lineup of 1-6 pokemon. In this, you'll be in a party, each with your own lineups. Going up against a trainer (gym leader or otherwise) by yourself would be tedious and boring for the others, as they'd be standing around, watching. There are a few options I can think of at this time. A. Battles are one trainer vs one trainer and the others wait their turn. Very unlikely we'd go with this cause that's lame. B. You encounter other parties such as your own and engage in multiple simultaneous battles, each player taking on a particular opponent's lineup. (This would include gym leaders as they no doubt have more traffic coming in than the video games imply so one gym leader could not possibly keep up with all the would-be pokemon masters coming in day and night.) C. You encounter other parties, as stated above, but you battle in one big skirmish instead of individual one-on-ones. Your party's lineups versus the other party's lineups. There can be limitations on the number of pokemon used by each trainer and/or limitations on how many pokemon can be on the field at once. When battling gym leaders for badges, you'd do so collectively in one big skirmish with similar rules applied. D. You encounter other parties as well as individual trainers but battle them in one fight. Instead of everyone using all the pokemon at their disposal, each trainer involved contributes a pokemon (or more than one) to a collective lineup with the standard limit of 1-6 pokemon. (Obviously it wouldn't actually be 1 pokemon in the lineup.) The lineup limit could be greater than 6 for party vs party battles, if we so choose. E. A combination of some or all of these, depending on circumstances and/or the desires of the players.