One question before I go on, for the Fae, as they would do something like that, why would Maeve do that? Like, do you think there's a compelling interest for her to do it outside of just because, even though Fae fit that bill?
As for the curse, I'm FAVORING kind of a mixture between a Loup Garou where she gets urges to be a mermaid, in addition to the normal situations where she would have to defend herself. I was thinking for that drowning as a possible impulse, some inspiration from normal mermaids and Pirates 4.
In addition, me personally (as its my character haha) I'm favoring a male turned female all the time, with the addition of the curse turning her into a mermaid. I was thinking it would be amusing of a 'learning yourself again' and getting into those awkward situations as simple as wearing a dress as a distraction but acting all manly cause of no experience as a lady. That's where Im a tad held up as I do want the Fae involved but I dont know how. I do like the idea of the Winter Court being involved however with Maeve or maybe even Mab, as shes the one who would seem powerful enough to permanent gender bend an individual and change their species at will. But, I dont know how or what history. That's also where I was thinking that the drama could be as its living with the consequences of being a mermaid as, well, I like the idea of being tempted but I also like it as well of no temptation and 'it is what it is and youre stuck with it period.'
To answer your first question, I'm guessing you haven't read the Dresden short story compilation
Side Jobs? In the "Something Borrowed" story Maeve gets one of her underlings to try to kill Georgia and ensnare Billy as a permanent thrall...for something that happened years prior (in
Summer Knight). I just chose her because she's vengeful and rude enough to do it - Mab certainly wouldn't be the only Fae powerful enough to gender swap somebody.
After thinking about it some more it actually seemed to make sense more to me though that a member of the
Summer Court would be more readily able to curse somebody with mermaid-ness and gender-swap. Biomancy (shaping flesh and what not) is one of the specialties found under Sponsored Magic: Seelie (Your Story pg 290) so a Fae from that Court would be more practiced at it. Additionally I imagine there's a Lea equivalent (aka a Titiana-second-in-command) in the Summer Court that minimum would be able to do biomancy and curses with ease. As for
why your character would be cursed, I think that's really up to you and figuring that out will help you determine the PC's personality and life experiences. The thing that would make sense to me the most would be that the character pissed off some lower-level mermaid servant and a higher-up Sidhe decided ironic punishment worked best, although I don't think the character would be considered a Fae at this point anyways - for the most part I think you have to be "born" into it (although you could include a Fae parentage as part of the backstory for it to make sense).
I'm not familiar with Pirates 4, but I feel like the drowning compulsion is a good idea. You could even really model it like Feeding Dependency: Drowning if you wanted to, but Feeding Dependency can be a pain in the butt for PCs from what I've gathered on here.
From a uniqueness perspective, the male-to-female swap seems to create more potential for interesting character behaviors, but I could see either working. Having to overcome suddenly be treated like a lady or being an office worker-turned-mermaid seem pretty unique to me.
If you have any further questions just continue posting here. Hope this helped somewhat!
Edit: Adding Incite Emotion seems like a smart idea to me, just depends of what kind of character idea/Power set you had in mind.
