I haven't got a build in mind or anything, but I was thinking about a winter witch for an Upcoming S&S game.
What do you think? Good idea? Bad idea? Maybe? and why please.
I am playing Skulls & Shackles with a multiclassed Witch(Winter Witch) 1. Currently character level 7. I don't think the extra's will influence S&S much if at all. The prestige class, however, does offer these:
Numbing Chill (Su)
Whenever the winter witch casts a spell that deals cold damage, she can imbue the spell with a debilitating eldritch chill as a swift action. She chooses one of the spell’s targets or a creature within the spell effect. If that creature takes cold damage from the spell, it must also succeed at a Fortitude save or take 1d4 points of Dexterity damage and be staggered for 1 round. The creature need only make this saving throw once per spell, even if the spell deals damage multiple times. If the target saves successfully, it is immune to this hex for 1 day. This is a cold effect.Blizzard Sight (Su)
At 6th level, a winter witch can see normally in natural or magical rain, sleet, hail, fog, snowstorms, blizzards, and similar weather conditions.
Note that Numbing Chill can be applied more than once per day per creature, but only until it makes its save. You can therefore make a creature helpless due to ability damage, allowing easy CdG. However, it does not come online until at least 10th level.
Blizzard Sight lets you see through many visual obstacles you can encounter in this AP. However, it does not come online until at least 11th level.
As I am a player, and not the GM, I don't know if these will substantially help in the AP.
As for playing a Witch in general, I think it can be fun. If it fits the role you want, go for it. There are several guides available, and they describe several roles you can easily do.
Lastly, check out the Skull & Shackles section. It may be a bit slower, but there are more likely AP specific advice here.
/cevah