Seventh Rejoining: There's definitely theory that the 'fuzzy memory' was the fault of the Calamity itself, but nothing clear to confirm if it was that or just another thing that happened at the same time.

The World of Darkness: That orb is actually the Cloud of Darkness itself, if we're thinking of the same orb!

Ark and Zot: There's no known connection. It might in fact be entirely coincidence, if you directly compare the Tower of Zot/Babil to the Void Arc/Pyramid of Mhach there actually isn't much in the way of commonalities aside from both being dark and bio-organic. But, both could've been invented by Ascians (we don't know what they were up to exactly in that era), so who can say?