There's also a book in the Blighted Village talking about the return of Thultanthar, which happened in 1372.
But all that aside, we might be getting a little off track. We've established the date for Moonhaven fairly well.
Personally, I think the village would be a bit more overgrown, and I think it's unlikely all the books would have weathered the last 120 years quite so well, but it is what it is; I can't deny the date.
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I'm curious why the Mind Flayers and Githyanki are involved.
What is the weapon? Is it sentient?
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The symbols worn by the Absolute cultists look like the symbols of Bane, Myrkul, and Bhaal.
Assuming there's a connection there, why would the Mind Flayers be working with them?
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Who do you think the Absolute is?
I suspect the Absolute is the Unclaimed.