Since I haven't seen it yet, I'm going to post a Steel-type Gym with 5 Pokemon. Looks like I'm 7th on the list of Gym Leaders that trainers will face...assuming Undrave is stuck being only the 4th gym in the league.
Pokemon:
Magnemite LV. 40 [Magnet Pull]
Magnet Bomb
Thundershock
Electo Ball
Flash Cannon
Bastiodon LV. 43 [Sturdy]
Take Down
Ancient Power
Metal Burst
Flash Cannon
Empoleon LV. 42 [Torrent]
Metal Claw
Aqua Jet
Fury Attack
Flash Cannon
Forretress Lv. 44 [Sturdy]
Mirror Shot
Take Down
Explosion
Flash Cannon
Klinklang LV. 50 [Plus]
Discharge
Gear Grind
Charge Beam
Flash Cannon
The Gym is an abandoned steel mill that was converted to the Pokemon gym. The puzzle behind this is balancing on girders that are hanging from the ceiling. There are switches that need to be flipped to power generators to lower the steel girders to the point of being able to walk on them.
Before the battle:
You've done well to get this far, but this is as far as you'll go. I've worked here my entire life alongside my Pokemon and we've learned that heat is what makes steel stronger. You'll see that the heat of battle makes me and my Pokemon stronger!
After the first non-KO hit:
Not too bad, but now you'll see how quickly the heat of battle makes my Pokemon stronger!
Down to last Pokemon:
This where we are at our strongest!
Last Pokemon at low health:
I seem to have underestimated the strength of your Pokemon, but now our true power will shine through!
Defeat:
It looks like you've proven to me that even when the heat of battle strikes, there is still the chance for steel to falter.
After battle:
You have proven yourself strong like steel. You have earned my respect as well as the Girder badge. All Pokemon become a little sturdier and will obey you if below level 80. Along with that, I want you have this TM. TM
Rematch Team:
Mawile LV. 52 [Intimidate]
Crunch
Sucker Punch
Vice Grip
Flash Cannon
Probopass LV. 55 [Sturdy]
Magnet Bomb
Thunder Wave
Power Gem
Zap Cannon
Ferrothorn LV. 53 [Iron Barbs]
Ingrain
Power Whip
Iron Head
Flash Cannon
Bronzong LV. 54 [Heatproof]
Gyro Ball
Extrasensory
Payback
Future Sight
Lucario LV. 51 [Inner Focus]
Aura Sphere
Heal Pulse
Bone Rush
Flash Cannon
Metagross LV. 57 [Clear Body]
Meteor Punch
Bullet Punch
Psychic
Zen Headbutt
Gym Music: "Harder, Better, Faster, Stronger" music only, no lyrics
Battle Theme: "Gentleman" - Psy