Shelby Mustang is a Centaur and is considered an Incubus although she has a body that shares a female's front end and a male's hind quarters.
It was one of her ancestors, Cathias, who mated with a centaur that survived the battle with the Lapith that would produce a child. The mating was virtually unnoticed and forgotten until the mid-18th Century when her great, great, grandmother was impregnated by an incubus.
Shelby grew up in isolation of knowledge of the demonic world, and would become a lesbian and work at a women's dance bar. It was a relationship with Agrat Bat Mahlat that interested Lilith Mephistopheles, who sent Excalibur and Crusader to contract her before Agrat could.
Shelby's demonic appearance is that of a humanoid/centaur due to the fact that her lineage for the past 3500 has Centaur bloodlines. Her skin color, a reddish orange, represents more her high sexuality. The most prominent feature is her gender, as her fore gender is of a female and her rear is of a male. Also complicating this gender mixing is the fact that her penis is that of a horse as opposed to a human penis. Shelby also sports a horse tail as opposed to the spaded tail of most succubi and incubi. Since Shelby can impregnate females as well as collect sperm from males, she is considered an incubus. Unlike hermaphrodite succubi that cannot convert semen to a demonic state, she is given the former title. To the best of anyone's knowledge, Shelby is a one of a kind incubus as there is no others in any of the other queens ranks, although it is possible there may be other centaurs roaming the mortal world, unaware of what they are due to the knowledge being lost over the generations.