>>48532747Normal type gym, all of the pokemon are themed around adapting/changing/flexibility in some fashion. My boys change type, change the weather, do all kinds of odd and fun shit to have a good time. Not the strongest gym without being artificially high level, but that's not really the point. Having the uncertainty factor is the goal.
Trainers in the gym would have changing pokemon rosters based on the player's Trainer ID as a seed, chosen from a small pool of options. The various rooms in the gym would change color and theming semi-randomly as well, and the Gym Leader's outfit would also change in each playthrough. Ideally, no two people would ever see the exact same gym twice, though the differences between each possible combination wouldn't be massive to keep reasonable difficulty.
Ideally, the Gym Leader's pokemon would all have one move, whether egg or TM-based, that's uncommon or rare to see, and this too would change between playthroughs, though the Pokemon itself would stay the same. Both for funzies and to show people new to the franchise some of the unusual things they can set up themselves.
Post-game, the gym leader and his trainers would have a secretary of some kind at the front of the gym, where the trainer could request to refight the gym, with specific "technique packages" to fight against. These would change the moves, abilities, and other characteristics of the gym's Pokemon to serve as sparring partners simulating certain battle strategies the player wished to practice against. The caveat is they'd have to be ones that Normal-types could perform, so it's not outright replicating the Battle Frontier or anything.