I have no idea what the "blighted gloom" in my terrifying biome embark even does. The expedition leader got caught in a bunch of it, and nothing obvious happened. Is there any way to figure out what these clouds do, or is it always thralling? Anyway, so far it hasn't got anyone.
One slightly terrifying moment was when I'd just got the entire crew downstairs after channeling down 2 z-layers from the embark block, dumping everything from the embark into a hole in the ground and digging outward from that, then bringing everyone downstairs. The blighted gloom followed us down two layers and swirled around for a while. I capped that and now the outside world and the caverns can be locked with three levers.
I did one of those "bring nothing but a pick and an axe and tons of ores and then build everything from scratch" embarks, which is pretty dicey with a terrifying biome, but it has so far failed to be very terrifying. I'm somewhat worried since I have no idea what this cloud does. I assume thralling, but how long does that take? Is it random? Or do some of these clouds do nothing?
I've dragged a bunch of wood and plants underground and just located an adamantine spire that, for a change, appears generous, have a general idea where magma is, and otherwise, was finally lucky enough to get an embark where my "grand staircase" just goes straight from the top of my fort directly down all the way to the magma, with no cheats or radar exploits.
I also finally got a trade depot multiple z-layers down connected to the surface by ramps to be accessible. Not sure why that was such a problem in the past.
Bringing all the components of bismuth bronze enabled me to get everything up quickly, but was soon superseded by actually having everything available for steel, as well as a ridiculously rich flux layer I'm actually using to build constructions at this point.
Waiting for the other shoe to drop in. . .the Fountains of Mastery.
Decided to play a bit after restarting to find out the name, and a Jabberer got in while the final bridge was being built and killed everyone except three dwarves and two children. Ironic name, really.