Ooh, Lucario statue. There's a door in the front of it too. Head on inside. Here you'll meet the Mega Evolution guru and once again see Korrina. Your friends will catch up as well. After much talking, it'll be decided that you should battle your rival. Here goes! Speak with your rival when you're ready and the battle will begin!
Rival Battle! - Pokemon Trainer Serenas/Calems Party
If Chespin was your starter
If Fennekin was your starter
If Froakie was your starter
After defeating your rival, Korrina will finally head to the Gym, so you can now go and take her on! You still can't head up the tower yet though as there's still a Black Belt stopping you. When you're ready, head to the Pokémon Center. Heal up, stock up on items and head to the Gym!
Tip #028: Spending Time In Pokemon-Amie
Traveling and battling non-stop is all nice and well, but don't forget to take breaks too. Even playing with Pokemon-Amie once in a while could help to keep things varied and stop you getting bored. Plus if you increase your affection, your Pokemon will gain slightly more experience in battle, occasionally break free from status conditions and more!