Okay, I'll lay it out for you.
Our game currently consists of 3 players and a GM. I am one of the players, and this is the first time the other three have played pathfinder.
Our GM is an old hand at Shadowrun and has some GMing experience there, but is still learning the system with Pathfinder.
Our Cleric is newer to gaming in general but has more experience with a fantasy setting, starting out with 4th edition of the other game and then rounding out his experience with a real game (Shadowrun again).
Finally, our rogue is the newest player, migrating in from computer games to Shadowrun before jumping in to our new Pathfinder campaign feet first. He is still learning to shake off the Computer Gamer Syndrome (EG attempting to 'go into stealth' at the start of each fight regardless of whether it's physically possible), but I think that with time he'll become a valuable member of the community. His character is a knife nut Half-Orc woman who seems to react largely on impulse, and is the main character of this story.
Okay, now some basic context. We met in a tavern to be employed to escort someone from one town to another. Stuff happens, and we flee with our new employer and end up taking shelter in a cave. The PCs have just met and haven't had time to get to know each other.
We go and explore the back of the cave when we come across a sleeping bear. Our Rogue panics and runs back, slamming straight into the cleric (Rogue rolled a 5 on a reflex save while the cleric rolled a natural 1) and waking the bear.
Long story short after some of the worst luck I've seen in all my years of gaming (seriously, we didn't even scratch the damn thing between the 3 of us and it consistently rolled in the 19's whenever we through spells at it! also, at least 2 fumbles in a singe combat) the other two were down and I beat a hasty retreat. Our GM adjourned for a while to try and work out how to salvage things then eventually came back and took the rogue aside.
So as the bear is about to deliver the cleric a killing blow the rogue leaps up behind it, glowing with evil-looking red energy, and cuts the bears head off in one strike with her dagger.
My first reaction is to quietly charm her, just in case (another natural 1 on the save by the way, so the GM has ruled a lingering affection effect), then go over and ask what happened. I didn't get a straight answer.
Out of character, the Rogue was contacted while dying by an unknown but probably Demonic entity of some description, the exact nature of which is currently up in the air.
Now the GM wants to introduce a subplot of the entity corrupting the rogue by offering her more and more power as she falls to the dark side (is currently neutral good). Some options we're looking at include offering and applying a fiendish template and, at some point of duress, having the rogue burst out into full half-fiend (This'll be at high level, where the template's power boost will be more in line with 'keep martial character up with two full casters' rather than 'one player getting favoritism'). Another option we're considering is having a familiar watch the rogue from the shadows for a bit and next level up appear before her and offer her power, sending her down the path of the witch (More specifically a witch/rogue/arcane trickster build).
So, I'm looking for suggestions for the nature of the pact holder (I'm suggesting a powerful Succubus, but any ideas are welcome) along with good tips for corrupting the PC. We would prefer each step to be a conscious choice on the character's part, preferably using power and the promise of power to do the corrupting for us. Thoughts?
A succubus works if the character is sexually attracted to her. If not, go for an Incubus. If you're looking for someone who would want to corrupt witches, Mestama, Demon Lord of Witches and Hags should do fine. She's a patron of Hags and loves corrupt "women who specialize in inflicting horrible cruelties via deception." This goes in line perfectly with a rogue who dabbles in magical power. She can take the disguise hex and trick people. Have her start slowly with first deceiving and destroying the truly evil, then more morally grey people, then have her be deceived in turn about the evilness of her latest kill. Have her rely more and more on the demonic power by engineering situations where she's alone against someone she can't reasonably beat on her own unless she taps into the evil power.
Have the character take improved familiar or even give it as a bonus feat to give her a Quasit. The Incubus/Succubus works as the tempter while the Quasit serves as the eyes and ears. When the Rogue makes more and more choices that lead to evil the Incubus/Succubus becomes more powerful (demonstrated b increased hit dice, class levels, or becoming a more powerful demon) as a reward for his/her success. In the end, the rogue/witch/arcane trickster as to make a choice as to who she's gonna throw her lot in with. Hopefully she picks the party which let's the Incubus/Succubus become the final boss of the subplot or even the main plot.