Riolu, the pre-evolution of Lucario, is hidden in the world of Pokemon Brilliant Diamond and Shining Pearl. This sought-after type of combat and steel will take some time to reach, but those who want to add Lucario to their roster will want to take the time to get Riolu. Here's where you can find it.
Before you can get your hands on Riolu, you'll need to reach Canalave City. Once there, she talks to the sailor about taking a tour of Iron Island. There is a cave on the island that you will need to enter. After entering the cave, he starts by taking the stairs to the right. This will lead to another room with an elevator at the end. Take the elevator down and you'll find two more flights of stairs. Take the stairs to the left.
At the bottom of the stairs, you'll find a well-dressed NPC named Riley. After helping Riley free Iron Island from Team Galatic's presence, he will give you an egg. Take an egg walk for a while and when it hatches you will have your Riolu.