The adventure I'm currently gamesmastering features one of these suckers.
However, I'm toying with the idea to change the story arc from merely "behind the scenes manipulator that goes down in a fight once the heroes meet up with it" to "this really makes me understand how dangerous Succubi really can be".
So. Upfront, I'm not going to promise I will stick to every last bit of RAW, but I would like to know when and where I am winging it :)
In short, how would the following approach work? Any advice on improvements? Feel free to point out where I'm breaking or bending a rule as written.
The non-spoilery background: There is a scripted encounter where the heroes finally catch up with the one corrupting their friends. It leads to combat, and the end of the Succubi. Let's call her Alenna.
Now, what if Alenna the Succubi simply Dimension Doors away when she realizes the heroes are too strong for her? And vows to return to wreak havoc using what she's good at, instead of what the heroes are good at (combat).
Her plan is to find out the sexual preference of the heroes, take an appropriate form, and approach each of them individually (such as when they're shopping in a Magic Shoppe, or posing as a paying customer at the circus etc). One of them meets Stellan The Armorcrafter, another one meets Sue the Potionmaker etc
She will start by using no magic, and simply appearing charming and persuasive, claiming to be able to bolster their prowess. In addition to the listed stat block, the adventure itself sets a precedent of an extra damage die (described as "demonic corruption") or the ability to summon demonic allies. Just as the description says, she's not (only) about lust for carnal pleasures. Players are often interested in plus bonuses more ;-) Bonuses to attacks, to damage, to skills, to their circus performance... (they're circus performers).
Remember, the point here isn't to hose the players. The point is to impress them enough to go "woah, now I really understood how our earlier friends could become corrupted!". As far as costs and drawbacks, I'm content with even Drained 1. The main thing is giving the players a choice to roleplay their characters as being tempted. And to do that, they can't feel their character's life is on the line. So I'm probably not even going to mention the negative damage (since even 18 points of damage is less than half their hp)
And of course, give them an opportunity to realize what's going on, set a trap for Alenna the temptress, and finally once and for all destroy her.
If general roleplay isn't enough to make them willingly accept her bonuses, Alenna can use Mind Reading and Suggestion.
What are the limits of these spells in this non-combat context? I'm guessing a PC needs to be lucky to resist (assuming the player suspects foul play and resists). The most interesting situation role-play-wise would be if some PCs successfully resist while others don't.
Again: I'm not planning to have her force PCs to do stuff their player doesn't want them to do. Except what's clearly delimited by CRB effects, of course. (Nobody gets upset their character does stupid or offensive stuff when under the influence of a Confusion spell, for instance. Even though a player having his character attacking another character would normally be a big fun-killing no-no).
I'm guessing one or three saving throws is all that stands between a PC and doing whatever non-specific stuff Alenna needs them to do in order to justify getting her "upgrades".
So one character runs back to their Circus to warn the others that Alenna is back. Another is just happy they've met Bob the Butcher who is not only their best new friend, but has also taught them how to gain +1 to their attacks.
PS. The party will be level 5 when this happens, making Alenna's DC of 26 quite respectable still (especially assuming the -2 penalty for finding her good-looking)