The dream persona offered vague explanations and promises. That is very different from what the guardian seems to be. From what I've seen, the guardian appears to be much more direct and straightforward, getting to the point.
Which leaves me thinking either:
1. it got rewritten/tweaked after devs read how the players were interpreting the character, or
2. It was intentionally vague in early access to hide truths about the plot and keep some mystery for release.
To me, this is a big enough change that it warrants playing and learning more about before any real insight is possible.
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Regarding divine intervention, sure. But that means the god has to choose to intervene. And the DM is the one who decides whether or not the deity in question intervenes. And Larian is the DM. Little bit of a circular thing going on here.
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Speculation that the guardian is Shar? Is there a good argument for that somewhere? I haven't seen anyone put forward that theory.
I'm open to possibilities, but I'm not sure I'm on board with that one without learning much more.