Describe the most significant technological advancement within this location.

Humanity is not the only source of technology.
The creatures beyond this world are not things of originality, but things of threads and patches, nightmares, songs and snatches, and of innovation by and by.
Addicts disappear all the time, and so some Fey came to realize they could easily take these vulnerables. It might have been inevitable that some would start to experiment and in the experiments something would be found.
It is a faerie art to build within the minds of sleepers, and this has been done since time out of mind. These constructs amuse their creators for a time, then shatter to nothing as the sleeper wakens. In the opioid addict some scrapped and jagged pieces remain, plaguing the burdened mind of the waking human as psychological disturbances.
One of the Faerie Host, its earlier name now lost, saw the potential to build onto these broken pieces as a foundation. What it used as the building blocks was its own essence, letting itself break and building again from the pieces each time its sleeper woke. The sleeper would break too, eventually, but the drugs gave it new fields to build in every where it looked. It built and broke and built and broke, examining itself as it began to understand what structures would stand and which would fall, taking on bits and pieces of legends and archetypes.
It was in the broken minds the Iron Mountain Order noticed its cast-off shells.
It is two weeks before Christmas, and the thing that built itself is now called Kris Kring Gale, a strange amalgamation of Mrs. Claus and the Krumpus. It knows it will be able to walk the earth for the week before Christmas, as does the Order. If it can do so, and if it can give out enough little addictive treats to the children, it will have what it needs to teach the others or its kind to come through.
Thus will begin the next great Riding. Thus will the Wyld Hunt begin again.