Quoted By:
Steel (Dark/Psycho/Ghost)
Unrealistic but it would look something like this. (Ignore the badges...just went for monochrome there)
This would not even be an 8. Gym leader. To many top Evolutions and more than 3 pokemon
The Dungeon would be a cave/grotto of some sort. The entry would look a something like the house in Fallarbor town in Hoenn, where you enter and find a cave in the back.
The puzzle itself revolves around metal duh and would include some easy riddle with this dot language from 3. Gen