My concept has bifurcated. I've been agonizing over choices, and it occurred to me it would be worth seeing if one branch or the other was preferable.
I've tried to summarize the core of the concept and mechanics, which means they're very brief.
Option 1: "Young Faust". This is Faust still young in his deal. He has just started to regret his deal for power, but not the power itself. Rather than outsiders, deal is with the Old Gods.
Mechanics: Occultist Arcanist. Feats SF(Conjuration), Augmented Summoning, then into Evolved summons.
Pro: Lots of summons, good choice of spells.
Con: LOTS of summons - it really is the best choice in pretty much every situation.
Option 2: "Old Faust". This is a Faust whose deal is really just a body swapping trick. Every 25 years or so he has traded bodies (and lives). He's been the villian in a thousand stories. He's had power. Was friends with Caromarc (through letters) for three bodies... always considered coming out to Caromarc and ending it all. Decided not to renew as his last body was failing, sent some evidence to Caromarc, but then panicked at the last minute. While weakened by the transference he's come to the funeral; in part to pay homage to his old - and only - friend, in part to check that the evidence (which is missing) does not show up. Or that it does, and he finally comes clean.
Mechanics: Spell Sage Wizard. In this case spell sage is representing some of his old power and previous lives. Probably look at Amateur Investigator, reflavoured for "previous experience" rather than "flashes of brilliance".
Pro: One amazing spell per day, awesome knowledge skills
Con: Novas in a single encounter, then just a knowledge guy (albeit an amazing knowledge guy)
I should probably also check; some of the roleplaying for this PC is going to be in internal voice (unless there's a group that would accept him... which I doubt!) - is this a problem?