Re: OOC
Well, the cliche thing to do would say "something from the abyss," and that was my original plan - a go between for Stan and Clementine. However, now that she herself is here, more interesting opportunities arise. I would like to see the familiar create, if not conflict, at least some moral dilemmas.
A struggle like Celestial vs. infernal is too problematic for my tastes. BUT, since Stan is Lawful Neutral I could see some excellent roleplaying opportunity in the chaotic vs lawful struggle. Right now, Clementine and Demios are both from the abyss (Chaotic-aligned plane), so I think it might make sense story-wise for Stan to get some kind of Lawful familiar. Maybe something very studious and organized, who is always pressing Stan to get back to academic pursuits instead of chasing around the planes.
It would have to be actually useful, of course, or pragmatic Stan and his chaotic family would have no reason to keep it around.
As far as actual creature type: I was thinking of taking Improved Familiar at my next level-up. I think an Imp fits all my visions for Stan's familiar - it hates both good and chaos, but it will have to either side with a non-evil lawful person (Stan), or two chaotic but similarly infernal beings (Clem and Demios) or it will lose every argument and get kicked out of the "family".
Unfortunately, most of the good improved familiar choices seem to require level 7, and I'll only be hitting six.