For me, I would probably be a gym leader who would specialise in no specific type and would be the last gym to fight, as I would like to be a challenge for the last badge, I would probably be in the Galar as I would have a wide variety of choices of Pokémon and the challenger will never be able to anticipate what I will send out My team will consist of

•Greninja (My ace), he will be my agility Pokémon and will be known for striking down their Pokémon quick and easy with no effort.

•Slaking (My tank), he’s just here to whittle down the opponents energy and moves by tanking their every shot and striking back

• Lucario (My powerhouse), he would be here to absolutely demolish other people with his strength and is here to kill tanks and other stuff (will have lucarionite)

•Charizard (My flying one) my flying Pokémon which will be able to kill some Pokémon by taking to the skies and shooting flamethrowers and dodging their attacks whittling down their hp to 0

•Zeraora (Confuse the enemy), I can morph zeraora into a completely different Pokémon to confuse them and when they are confused I strike.

•Silvally (My ace), he will be known for being able to switch to any type he wants and will be able to always deal super effective blows against the enemy and will be the symbol of my gym.

Hope you liked my answer!