So much frustration for the Things Fall Apart achievement. This has been my hardest achievement yet I think. It's tough playing badly.
Took several reloads to get my era score low enough for a dark age for this save file. I had 2 prior dark ages, but only had 3 cities flip. Maybe the problem is I didn't understand the mechanic properly, since I wasn't around when the patch came out and didn't pay attention to patch notes/video. The way the cities flip seem so random. Even in my save file I had 4 cities that should have flipped, but only 3 did (luckily one on my main continent flipped). The city was at -20 loyalty and did not flip. I tried getting this achievement playing relatively normally (but slightly bad), but I couldn't get it. I had to really stupidly and aggressively place my cities (which is where I was running into era score problems). This might have been easier on deity, but then you run the risk of the AI attacking you. Of course I did get attacked by the dastardly Mapuche, but they were far off and only sent 3 corps units.
Things Fall Apart: Press end turn, and provided there's not some weird RNG with this mechanic, you should get 4 cities flip. I'm pretty sure I saved this file after I settled the cities, if not, settle the 4 cities then press end turn.
No Light Without the Dark: Slot in both the dark and golden age policies.
Dead But Dreaming: Use the governor promotion to finish out the Voidsingers governor promotion tree.
I'll probably edit in the last secret society achievement later today, Voices of Aiwass. And I think that's it for my achievements other than the Red Death ones I need to crank out.
EDIT:
Voices of Aiwass: Use the governor promotion to finish out the Hermetic Order governor tree.
And I also have an Ethiopia victory save if anyone needs the win as Menelik. Because it's a culture victory, I saved it the turn before victory, so you'll have to play through the following turn.