Creature Description
Lucario is a bipedal, jackal-like Pokémon that is 3'11" in height and is generally agreed to resemble the Egyptian deity Anubis. Lucario is a Fighting and Steel-type Pokémon that evolves from Riolu; in the Pokémon RPGs, Riolu evolves when it gains a level while its "Happiness" rating has achieved a high-enough point, and only during morning, daytime, and afternoon hours. Lucario is able to detect and wield an energy named Aura, a sort of force that surrounds every living thing. According to the Pokédex, by picking up on the aura emanating from others, it can read their thoughts and movements, and a well-trained individual can sense and take in the feelings of creatures over half a mile away. It understands human speech and even communicate telepathically in human languages.
 Pre-release Confirmation
Lucario is a secret character that was leaked before the game was released.
On January 21, 2008, a promotional video for Super Smash Bros. Brawl on the official Wii website was posted that showed a Groudon sticker being highlighted and the faces of Pikachu, Pokémon Trainer, Lucario, and Jigglypuff to show that the sticker can be used to power-up these four characters in Adventure Mode. This was essentially a confirmation that Lucario would be a playable character in the game. This video can be viewed here.
A link to the official websites page containing information about Lucario's moves in Brawl is here.
 As a Playable Character
Lucario is unique in that the more damage it takes, the more damage, range, and knockback its own attacks have (based on the actual ability of most Lucario in the Pokémon series). This only applies to its Aura-powered attacks, noted by a bluish flame or aura. A few of Lucario's attacks don't use Aura, such as its dash attack and back throw, among others. This trait makes it not particularly useful at the beginning of a life, but by surviving to a high damage level, it becomes ridiculously deadly.
Its neutral special attack is a chargeable ranged blast comparable to Samus's Charge Shot. Its side special is a short range blast, or at point blank, a throw. Its up special is a non-damaging recovery move, it will move in any direction pressed. Its down special is a counter attack, that is, it will harm a character who tries to attack it within a brief time period. It is an Aura-powered counter, and its damage caps at about 15%.
It is not particularly fast moving, but can escape many tight situations. It is slightly slower than average.
Lucario can wall jump, and has a surprisingly very high wall jump. It also possess a unique ability of being able to wall jump off the same wall an almost infinite number of times, effectively allowing it to climb walls. It also has a "cling" ability, which lets it cling onto walls before wall jumping. Lucario has a similar moving style to Mewtwo, from Melee.
Lucario is currently ranked 11th on the tier list, in C+ tier.
 Trophy Description
An Aura Pokémon. It can track energy called Aura, which is given off by all living creatures. It's a unique combination of both Fighting and Steel-type Pokémon. Lucario evolves from Riolu during the day if its happiness has reached its maximum point. It specializes in attacks that use Aura energy, like Dark Pulse and a can't-miss technique, Aura Sphere.