Here's how you can do it in Pokemon Mystery Dungeons:
1. Increase Riolu's Friendship: Friendship is determined by how much you use and care for your Pokemon. Here are some ways to increase friendship:
* Use Riolu in battles: Make sure it's a part of your main team and participates in battles regularly.
* Feed Riolu its favorite foods: Riolu's favorite foods are Lum Berries, Oran Berries, and Sitrus Berries. These berries can be found in shops or as treasure in dungeons.
* Use Riolu for errands: Help other Pokemon with their requests to build up Riolu's friendship.
* Talk to Riolu: Interact with Riolu in your base camp, and choose the options that show you care for it.
* Give Riolu special items: Certain items like the Friendship Ribbon can boost friendship more quickly.
2. Level Up: As you battle and complete dungeons, Riolu will gain experience points and level up. Once Riolu is at a high enough friendship level and levels up, it will evolve into Lucario.
Note: The exact level at which Riolu evolves can vary slightly, but it usually happens around level 30.
Tips for increasing friendship:
* Use Riolu as your leader: The leader of your team gains friendship faster than other members.
* Use the Friendship Checker: Talk to the Friendship Checker in your base camp to see how high your Riolu's friendship is.
* Don't let Riolu faint often: Faints can decrease friendship, so be sure to keep Riolu healthy during battles.
Good luck evolving your Riolu into a powerful Lucario!