Lucario is Negi's third Pokemon he caught and debuted as a Riolu. He evolved into Lucario during a battle against Evangeline's Skorupi and won with a newly-learned Aura Sphere. He officially appeared in the second season of Full Moon's Full Pokemon Journey, in the same episode, he mega evolved and had no problems controlling it.
Despite his evolution into Lucario, he has the ability to read people's minds by sensing his aura which was stated by Negi Springfield, and even mentioned his ability was Steadfast.
He also has great instincts which occurred in the second season of Full Moon's Full Pokemon Journey and because of this, Lucario has been a vital powerhouse of Negi's team. He can also use his aura to find hidden objects in hidden spots such as Team Rocket, wild Pokemon and hidden items.
Lucario's known moves are: Aura Sphere, Dragon Pulse, Earthquake, Calm Mind, and his ability is Steadfast. As a Mega Lucario, his ability is Adaptability.