Fiends' magical nature allows them to crossbreed with virtually any creature. Spawned deep in the dark, nether planes, these fiendish offspring are abominations that plague the mortal creatures.

Demons and devils bring their progeny along to the Material Plane and loose them upon the world. Sometimes, however, fiends force themselves on mortal creatures to create evil half-breeds. The more depraved creatures are sometimes even willing to participate. Although half-fiend offspring are usually destroyed at birth, some survive to become grotesque mockeries of their mortal parents. All too rarely, though, one learns form and takes on the characteristics of its nonfiendish parent, turning from its evil heritage.

No matter the form, half-fiends are always hideous to behold, having dark scales, horns, glowing red eyes, batwings, a fetid odor, or some other obvious sign that they are tainted with evil.

Never truly fitting into any mortal society, half fiends are usually loners. In the infernal planes, they are mistreated and derided for their impure nature. Among non-fiends, they are outcasts, hated corruptions of natural order. Humanoid half-fiends are sometimes called "cambions." They often serve more powerful fiends or lead evil creatures on the Material Plane.

Devils. LE! A secret lurve of mine.

Book of Vile Darkness is probably your best bet. Crafty, not nuts. Malicious in a very intelligent way. Manipulative. They won't like demons very much and they'd likely abhor anything celestial, or it'd be against their nature to depending on how much of his Infernal side you want to let through.

Being good and being devil blooded would likely be a very large struggle.