So I might be making an occasional appearance in a campaign. I'm supposed to make a character the usual group won't really like, but won't hate enough to murder and wreck the campaign. Powerful, useful, and never completely trusted. But also nothing that will eclipse the main party. Maybe more powerful in her specialty, but not outside of it. Will start at probably 6th or 7th level and advance in parallel with the group. Maybe a level behind them.
If you have read the Hidden Legacy series by Ilona Andrews, there is an old woman named Victoria Tremaine. One the world's most powerful and ruthless truth seekers. She can tell when anyone lies with no effort. And if she needs info from someone, she has no compunctions about cracking their mind like an egg to get what she wants. With zero regard to what is left afterwards. Her own mind is the most powerful of vaults.
I'm thinking about making a character based on that. Now PF1e has a lot of abilities like that. Oracle's brain drain revelation. Inquisitor's detect lies. The detect thoughts line of spells. The occult book (I have very little experience with that) has a bunch of straight mental attacks and defenses.
They use 20 point buy.
Most any race that is usual can be considered for PC's, but I don't think the concept would work with too monstrous of a race. It is supposed to be a monstrous personality in frail old grandma.
Any PF books.
VMC is allowed.
Unlike most characters, I'm really not worried about general usefulness in most situations or general combat ability.
So, what is the build that can get me the most of those abilities and spells at useful DC's.
Offensive will-save effects; a mesmerist might be the answer here. A dreamstalker mesmerist gets hexes to further debuff the target and a bunch of mindscape spells which might be relevant too.
As far as race goes, gathlain, gnome or halfling get extra uses of mesmerist tricks which matters to a dreamstalker especially.
Ambuscading spell and improved initiative might be relevant feats if she only really wants to get a single spell off.
I'd go psychic. Not just knowing whether someone lies or not but being able to change their memories ... and mostly anything else.