Huh. That shadows thing is fairly neat. Second go converted a city to fishmen, opened the maligned gates, and unleashed the shoggoth before anyone could stop me... twice, the second time after my enthralled lord had been murdered and the sole controlled city occupied, the population dutifully finishing the ritual in front of what were apparently very confused or very lazy liberators. Said shoggoths proceeded to devour every living thing on the planet... except one city. That they/it (at some point the two joined bodies and became one larger shoggoth) surrounded, constantly attacked, and couldn't kill. Enthralled the city's leader, assassinated every other member for the society's leaders, tore down its defensive structures, built temples to the moon and converted half the population to somnulents, or whatever it was... and ultimately lost.
The light held off the darkness, murdered down to the last five or so thousand humans, half of them slaves to a crippled god, with the one last sanctuary of humanity surrounded by literal miles of shoggoth that were apparently too lazy to actually go inside and eat the entirely undefended encampment. I can only assume the constant rebellions popping up to be immediately eaten by the shoggoths were some kind of sacrifice scheme the gibbering remains of mankind enacted to pacify the beasts, and the bright future is an eternity of tossing one out of every ten or so people into the world beasts that have became their new existence. Definitely a work in progress, but it's pretty neat regardless.
... part of me thinks maybe I don't quite get this whole subtle spreading darkness thing, though. I mean, it still counts if everyone's been eaten after half the world united to destroy my fish city, right?