Originally Posted by
Mr._Blinky
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Yeah, those are pretty much the same reasons I came up with, but it still just feels weird to me. I just don't know why a wizard like Merlin's first choice of place to put his Super-Max Prison would be in the middle of Lake Michigan; I get the idea of isolation, but why would that even be a place he'd necessarily know to consider? It's not too much of a stretch for me, it's just a little...odd.
One thing to remember on that last point of yours though: the Ley Lines exist because of Demonreach, not the other way around. It's specifically stated that the Demonreach is the source of those Ley Lines due to the ridiculous density of Eldritch Abominations stored there.
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Isn't it obvious? It's because Harry goes on a spree of time traveling/alternate Harry creation. As such he is himself Merlin, Rashid, AND Harry. Which, while sarcastic and entirely crazy, would explain a surprising number of things.