Hum interesting. As I've said to my RL friends, I'm (or gonna be) a Draconic Master. I'd be like gym leader #8 or an elite four member, using draconic pokés to destroy and burn and... well. Anyway, I'd say that if a trainer faced me for the first time, I'd be using -Kingdra lvl 45 -Haxorus lvl 52 -Flygon lvl 47
-Altaria lvl 44 -Charizard lvl 48 -Gyarados lvl 50
The gym would be divided in 2 sections, the first one depicting a somber cave with dragon bones to decorate and you have to use strenght to move boulders and advance thorough. After that you'd have to go one floor up and appear in a puzzle room filled with fire breathing pokedragon statues that wont let you advance unless you press the corresponding switch( and face my minions while trying to so buahahah).
As a reward I'd give the victor TM 02 Dragon Claw. Also, I'd play a role later on the game helping the player to face *insert game version evil team here* and unblocking some area.