What should this tiefling victim be?

[Sejs]

Rogue/Gatecrasher for some particular faction - sleeper agent, spy, and informant.

 

[Stormborn]

If someone suspects she is evil, make sure she isn't. Perhaps she is a member of a "Redeemer" cult - one that seeks to turn evil outsiders good. She is filled with self-doubt and loathing as she is a new initiate and hasn't been able to work through her place in it. She wants to be good, but is having trouble even understanding what that means because she's never really done anything "evil" (although she doesn't really think that). Perhaps she was recruited by a friend, lover, or sibling to the group, and is really loyal to them first and the group second. She wants to be loved, belong, etc.

The Redeemer cult is outlawed in the city and is thought of as a minor irritant, but is actually larger than people think. Key lieutenants, maybe even a general or his aid, have been converted. They all get a small tatoo or item that allows them to conceal their alignment. They are making plans with a force of Good outsiders to take the city.

As for class, just make her an "expert" or possibly a Beguiler or Bard if you want her to have levels in a PC class. She is a victim, but one that is trying really hard to not be one and is in the process where she could go either way.

Depending on the PCs they can either help her, be used by her (remember she isn't fully sure about good and evil yet - CN trying hard to be CG and failing), or use her to win favor with the powers that be.

 

[Nightfall]

Come on...Incarnate Voady. While alignment might not affect the planes, it's still good for incarnates!