Lucario

Lucario is a playable character in Super Smash Bros. Brawl, entering from the Pokémon series 4th Generation of games. Like Pikachu, this Lucario is male. He uses his Aura abilities for his many attacks, and is very quick and agile. Lucario will play a part in the Subspace Emissary, in which he will assist Snake at some point in the game. He also appears to fight Meta Knight at one point in the story. Afterwards, Lucario and Meta Knight team up. They later board the Halberd, and team up with Snake.

Lucario appears to have replaced Mewtwo, another Super Smash Bros. fighter from the Pokémon series who was only playable in Super Smash Bros. Melee.

Lucario has a special property no one else in Brawl has - the more damaged Lucario is, the more damage and knockback all his attacks do. It seems to max out at 200% damage. A move that normally did 15% damage did 26% damage when he was at 200%, and knocked the opponent back about twice as far as normal.

Recently, two gameplay videos have been found. They can be found here and here.

Lucario
''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 a certain point. It specializes in attacks that use Aura energy, like Dark Pulse and a can't-miss technique, Aura Sphere.''

Lucario (Final Smash)
''Lucario's Final Smash. After flying off the screen, Lucario reappears in its center. He then launches a powerful Aura attack against all foes within a certain distance. The key to this attack is the ability to change its angle--it's a must to sweep slowly left and right to hit selected enemies multiple times. The last blow will send the victim flying away.''