Luxio, for a Pokemon, has a fairly complex design. Its pre-evolution, Shinx, was first confused for a mouse when it was first revealed due to its round ears. But Luxio, and its evolutions, are clearly based off lions. If Shinx is a lion cub and Luxray is a fully grown lion, then Luxio is an adolescent, depicted as a lion with its mane partially grown. It is a quadrupedal beast with fur that seems to spike around its head and at the base of its tail. Emerging from the spike of fur is it tail, that has what appears to be a four-pointed star that mimics a lion's puff of hair.
Luxio's fur is an assortment of colors: blue, black, yellow, and it even has a red nose. In the first generation of Pokemon, most mammalian electric-type Pokemon were yellow or at least had patches of yellow somewhere in their design. Luxio still retains traces of yellow in its design but a majority of its body is blue and black. Even though we think of electric as yellow, most common forms of electricity that we may see are actually blue. The color "electric blue" was made to resemble the color of an electric spark. And, since Luxio is the "Spark Pokemon", we now see why it is blue. The aforementioned star at the tip of Luxio's tail may resemble a spark of electricity as well.
Before I dive too deeply in the supposed inspirations for its design, there are some theories that Luxo may possibly resemble a Sphinx; a half-lion, half-human creature from Egyptian lore. Though I do not want to discredit this theory, I believe that there is very little design influence from the Sphinx. Luxio's mane could resemble the crown that the Great Sphinx wears but Luxio lacks any sort of features that resembles that of a human. The only similarity I see are the traits both creatures share with the lion.