Just a heads up on the terminology that I'm using so we're all on the same page. Fiend is any outsider with the evil subtype. Devil is anything with the Lawful and Evil subtypes. Demon is anything with the Chaotic and Evil subtypes. Each of those later two subtypes have races and species within them them, so Asura, Baatezu and Kytons are all forms of Devils; Lomura, Tanar'ri and Qlippoth are all forms of Demons. Other things, such as Hoardlings, Yugoloths, Daemons and Night Hags simply fall under the category of fiends.