As for #1: It's the Sky Fortress, and its purpose is about the same as the Hellcastle, which is to give you a means to mine its material, and a way to summon a new boss(the Dragon Lord). It also has more coinage in its chest than the Hellcastle's chest. #2: The comets should be appearing... They appear as circles of Ever Ice, sometimes buried in a Corruption chasm. And they're kinda small, too. Not nearly as big as a meteorite. Um... still not actually sure. I did just realize that I changed something in one of the newer versions to stop custom NPCs from spawning near town NPCs, but then, that's just for custom NPCs. Do you mean that ALL NPCs aren't spawning?