In Pokemon Black and White, the fourth gym is the Nimbasa City Gym. The Gym Leader is Elesa, a well-known model in the Unova region.
But before you can challenge the gym, N appears and takes you to the Ferris Wheel. You and him will ride it and then he’ll challenge you to a battle. But, once again, that’s a different story. After you defest him, you can now challenge the gym.
When you enter the gym, talk to Clyde and receive a Fresh Water. The entire gym is based on a roller coaster. Walk straight to the blue-lined roller coaster and ride it to the platform on the right. Exit that and head to the right and then go up. You’ll then be challenged by Lady Magnolia. Defeat her then continue going up and press the blue switch. Go back to the entry way, and you’ll ride that roller coaster to a different platform.
Exit that car and go left, then up. You’ll then be challenged by Rich Boy Cody. After you defeat him, press the yellow switch to change the path on the yellow roller coaster. However, when you try to enter that car, Rich Boy Rolan will exit the car and challenge you to a battle. Defeat him, and then enter the car.
Exit that car after you have been driven around to another platform. Press the purple switch and it’ll change the path on the roller coaster. But when you try to enter the car, Lady Colette will exit the car and challenge you to a battle. Defeat her and the enter the car.
You will then be taken to the platform with the Gym Leader on it. Defeat her, then press the red switch to change yet another roller coaster’s path. That’ll take you down to the entrance.
Elesa has a lv25 Emolga, another lv25 Emolga, and a lv27 Zebstrika. Both of her Emolga have the same moveset. They also have the same ability: Static, which paralyzes your Pokemon on contact. They tend to use Aerial Ace and Volt Switch. Her Zebstrika knows Flame Charge and Volt Switch. When you defeat her, you’ll receive the Bolt Badge and TM72 which is Volt Switch.