A Shiny Lucario is a rare Pokémon that is colored differently than the normal Fighting and Steel type Pokémon Lucario. The regular Lucario is blue and black with a cream-colored chest, but the Shiny Lucario is yellow and black with a blue chest.
Shiny Pokémon can be encountered in the wild, but they are very rare. Shiny Pokémon first appeared in Generation II of the game series and feature an alternative rare color. Shinies are recognizable by their different coloration and by the stars that surround them when they are encountered. The term "shiny" was first coined by players themselves when the first alternative-colored Pokémon appeared in Generation II.