wait its confirmed shes a selunite?
astarion claimed to remember the hopskotch game in blighted town as well so i thought that was debunked
Nothing is confirmed. It's a theory on this point.
Any character might comment on the hopscotch, but there are at least two other potential places round Moonhaven (behind the windmill and in the old school) where Shadowheart might react and be overtaken by strange magic. And Moonhaven is linked by some of the notes you find with a (heretic?) Selunite sect. Well, and there’s its name, implying a connection with Selune.
Shadowheart’s reaction implies that she might have some connection with the village, but it was destroyed around a hundred years before BG3 (I think. I confess I haven’t quite got the timeline right in my head as so few of the notes have dates on them). If Shadowheart is from there then I think chances are she was pretty young at the time. Especially as we now have Jaheira to compare her with, who Larian are showing as greying and middle aged, and I think they said they’d assumed she was around 150-ish? So Shadowheart might turn out to have been kidnapped by Sharrans (working for Ketheric Thorm?) from Moonhaven as a child and raised in the Sharran faith, and perhaps have even been at Gymforge at some point, or even when it fell. I think that could be fun, as it gives her multiple connections with places you visit on your journey (probably including Moonrise Towers too), and the quest Find the Nightsong. But she would still be a Sharran in this option, though discovering her history might cause her to question some stuff.
Or she’s from Moonhaven but not kidnapped by Sharrans as a youngster, or not from Moonhaven at all, but maybe is Selunite and that’s her “true” god trying to reach her in those spots in Moonhaven. In that case, she might be a Selunite subverted just before her last mission, or one that had been with the Sharrans for a while. She might even have joined the Sharrans intentionally, undercover. What she knows of herself might have been wiped from her memory just before her last mission, or her memory could already have been manipulated before that.
Or she could genuinely be a Sharran with no connection with Selune at all, but who lost some other important information as a result of the mental meddling, perhaps she had some doubts about the most evil elements of her religion before her memory was wiped, or was otherwise something of a heretic. Or was a true Sharran with no doubts, and genuinely believed her religion served an important purpose (her spiel about stripping back lies and illusion was pretty compelling) but finds herself so changed by her experiences of living without her memories that when she gets them back she no longer fits back into her old life (I guess this is the closest to the chaotic evil mf option).
But as long as she turns out to be NEITHER a random kidnapped civilian NOR a straightforwardly chaotic evil character, I’m sure I’ll be interested in her story!
