You know what? Forget types, my gym will be based off of the theme of Pokémon who are draconic. So basically, Pokémon who are either a Dragon-type or Pokémon who are in the Dragon Egg Group or any reptile who's not in the group. After seeing Raihan's gym, I wanted to see more of Pokémon basing gyms off of themes rather than types. My gym will be based in a castle filled with artwork from the bestiary (all drawn by me), dragon statues, and the like and the player has to find clues (interacting with trainers, exploring rooms, etc) to find keys to eventually unlock the main gate leading to me. The player sees the 8th gym leader standing before them in a grand courthouse, the trumpets roar as the challenge has been accepted. I see that the challengers' Pokémon is injured so for a fair duel, I ask them to enjoy some food and rest for a little bit before fighting me at night. Afterwards, the challenge can begin and before the trainer stands this team:
I haven't thought of any quotes yet but I award the trainer with the Royal Badge (will make art of that too) and I give the trainer TM 99 Breaking Swipe. Should the trainer fail, they will have to train harder before doing the challenge all over again.
(This might be on the tougher side and definitely different but people have been wanting the games to be tougher as well as the formula to be shaken up. Of course, if the difficulty selection is back then the Pokémon's levels and movesets can be decreased or increased.)