While I admit that these types of roles have been frequent enough to become a running joke among the Scarab/Scion Immortals' Alumni Association, a couple of guidelines:

1) As a general rule, devils are of Orderly ethos and demons are of Chaotic ethos. One would assume that if their bloodline forces people to be evil, murderous bastards, it might also influence their ethos.
2) I recommend diluting the bloodline. If one claims that one is the direct offspring of some arch-devil, it looks sad when Hidden Forest trolls stab one down. Also, it makes me want to set you vulnerable to holy damage.
3) Consider adding in sinful personality characteristics other than "I like murdering people, unless they look stronger than me, or if it looks risky, or if they don't have good gear I can use or something." Your literary underworld figures often suffer from an excess of Pride, Wrath, Gluttony, and the like. Some of these characteristics will help you stand out from the legions of other characters with half-demon roles.

valguarnera@carrionfields.com

I have been reading the First Law Trilogy by Joe Abercrombie and I was going to do a role based on Ferro with a little demon/devil way back in the family tree. After reading this I'm going to have to come up with a new role! :P

It is always amusing when you are reading one of these roles, and before you can finish the first entry, the direct-offspring-of-unspeakable-evil-with-curiously-wrong-ethos-thrown-in gets pasted by Arbitrary Low-level Gnome.

valguarnera@carrionfields.com

Fear the WIS.

did they respond with 'I'm going to tell my Daaad!' I think a wimpy, whiny half-demon would be rather humorous. Kinda like a 'little Nikki'.

I play that the human side of me makes me all froofy and the other demons/slash devils made fun of me so I I hate dwarves and paved streets in order to fit in.

w00t, nice post.

asf

Rolling up my half-angel now...

Half-angel would be easy enough to do with a paladin.
If you're going half-demon (I maintain halfs should all be human/elf cause stats don't make sense otherwise and anytime I see otherwise I find it kind of non-sensical, but hey, it's a fantasy world so I go along with it)

If you're making up some fictitious half breed, make a good story and do something interesting. Go whitecloak style paladin with the half-devil role (for the orderly part), select some evil IMM, get your powers back and become emperor, then kill everything in your path. Easy to come up with a role fitting of that story line, and even make it doable. Hell, if you put actual effort into rp'ing it you may even survive long enough to get powers back.

So much more interesting than I'm evil cause a demon banged my mom, now I'm evil too, and i'm half demon. Now let me join random evil cabal and just kill things.