Lucario was used in Steeling Peace of Mind! to help Ash, Dawn, Brock, and Barry figure out why the Steel-type Pokémon were acting strange. Even though it was a Steel-type it was protecting itself with Aura, but something more powerful than Lucario's Aura made Lucario going to berserk and started to attack his master.
Riley used his Aura to protect himself and his friends. Pikachu used Thunderbolt to calm it down, but Lucario went to the source, which is Team Galactic attempting to open the ruins. While Ash's Pikachu destroyed the source, Team Galactic set up bombs around the island. Fortunately, Lucario and Riley used their Aura to encase the blast and move it in the sky, thus saving the island.