Versus Fighting-type Pokemon
Double Damage : Flying, Psychic, Fairy
Normal Damage : Normal, Fire, Water, Grass, Electric, Ice, Fighting, Poison, Ground, Ghost, Dragon, Steel
Half Damage : Bug, Rock, Dark
No Damage : None
Here we are at the third gym! Look keen! This is a Fighting-type gym, so the types listed above are good or bad, depending on which ones you're looking at. The gym itself is a roller skating arena. Move up to the rail, then got on your roller skates and charge at it. You'll jump on and slide to the other side.
As roller skaters move past they'll challenge you. Each has their own set path and you need to defeat them all before you can challenge the leader, as pieces of a bridge slowly move into place with each trainer beaten. The member that will move by the point where you entered the arena is as follows:
Gym Member Battle: Roller Skater Kate
The one moving around the three cones to your west is keen for some battles too.
Gym Member Battle: Roller Skater Shun
There's another person to the north, doing a sort of figure eight. Get in her way and she'll take you on.
Gym Member Battle: Roller Skater Rolanda
Head to the south-west area of the arena to find the last of the gym members. Here we go!
Gym Member Battle: Roller Skater Dash
After defeating the fourth and final gym member, you'll be able to reach Korrina in the centre of the gym. Ride the rail there, although you might want to head back to the Pokémon Center and heal and stock up on items. Once you're ready to go, speak with her!
Gym Leader Battle! Leader Korrina
Note: Korrina can use Two Hyper Potions mid-battle to heal her Pokémon.
Mienfoo and Machoke are a simple affair, being pure Fighting-types, so just refer to the type list to see where you stand. Hawlucha is slightly more complicated, since it's a Flying-type too, but it barely makes a difference for your Psychic, Flying or Fairy-type Pokemon.
After defeating Leader Korrina, you'll receive the Rumble Badge . This means that any Pokemon up to Level 50 that you received in a trade will obey. Do a little dance! You'll also be able to use Surf outside of battle. As well as that you'll get give TM98 - Power-Up Punch for your efforts.
Back to the Tower of Mastery
Now that you're all done; she'll ask you to battle her for a third freaking time, back in the Tower of Mastery. Put your skates back on and take the south rail out of the area. You'll wind up back at the start of the gym. Head outside, heal your Pokemon then head to the top of the Tower of Mastery.
Make sure you stop by the third room on the way up and talk to the guy with purple hair. He'll give you TM47 - Low Sweep . Once you're at the top of the tower, talk with Korrina and she'll give you a Mega Ring . Now you can mega evolve. OH YEAH! Turns out Korrina's Lucario also wants to fight for you, so let's try it out! Let the battle begin!
Trainer Battle: Successor Korrina
Easy Win! When the battle begins; enter the Fight screen and click the Mega Evolution button. From there, choose your move and attack! Just use Power-Up Punch twice now and you should win. Easy; but it was only meant to be a tutorial. If you lose, no sweat; it's not a real battle.
After that epic battle, you'll be asked by Korrina if you wish to take the Lucario you just fought with, with you. Obviously say yes! After that you'll be done talking, so head back outside. It's time to head out of Shalour City. Take the east exit, to Route 12!
As you're leaving, your rival will appear and give you HM03 - Surf . This is one of the better HMs for sure, doing impressive damage in battle and letting you travel across water on the field. Teach it to your best Water Pokemon and never look back (until you get Scald or Waterfall)!
Tip #029: Mega Evolution
After receiving the Mega Ring , you can Mega Evolve Pokemon! Not all Pokemon can Mega Evolve, but those that can must be holding onto a Mega Stone - in Lucario's case, the Lucarionite. If you have a Lucario already, feel free to give it the Lucarionite. Also note that only one Pokemon can Mega Evolve per battle, but in the main story, one's well enough!