So yes, shedim.
I'm rather interested in them for fleshing out the environment we're playing in some, so I turned to Street Magic since I recalled seeing them in there along with the toxics and their ilk. However, the information in there, I found rather cursory. What other sources would you recommend I turn to, in current and older editions, or even novels?

Also, what are your own thoughts on them? How have or would you use them? At what kind of Force levels would you think they actually create the threat they're portrayed as to be, both to the world at large and to actual runners? Seems to me like as long as you keep some distance between them and you, the average Longarms user wouldn't have too much trouble picking them off, with just their Fear power being available to them outside of shambling range.

My group is currently playing in the United Netherlands, in and around the Europort sprawl, which means having a truckload of previously highly populated environment that's been flooded with the Black Tide's toxic sludge. How likely would you think encounters with shedim would be in there, given that the actual flood happened sixty years ago? I'm assuming most bodies would have rotten away by the Year of the Comet, but then, I'm more playing with the idea of using would-be looters, bog bodies, or even marine life, coming in from the rivers. Is there anything actually preventing shedim from possessing animals?

Mostly for my fellow Dutchie Ascaphalus here, but everyone else as well of course: what do you think?

On a sidenote, I wonder: have any of you actually ever used the UNL for a setting?

Well, Shedim are reasonably strong, if you play them smart. Remember, they are possession spirits, so they can wear armor on top of ItNW. I used a pair of F6 shedim (the standard ones), and it was nearly a TPK for a high powered group. Their main source of power isn't physical combat; it's mindrape and cc. Make excessive use out of fear and compulsion, accompanied by "Would you kindly...", e.g. "Would you (the streetsam) kindly shoot (insert party member X)". Make sure Mr Longarms user is never actually firing at the shedim; keep him busy killing his own teammates.

About the bodies: Shedim can have regeneration, and some fluff text suggests that corpses, when possessed by someone with regeneration, heal back to the point of appearing alive and healthy.

I feel that shedim should not be a direct threat, D&D random encounter style: "You enter a clearing to see three shedim-possessed corpses rise from high grass to attack you". Rather, they should use their possession and magic to the max - like that guy heading the Great Jihad (sorry, away from the books now, can't look the name up). Just like head corp honchos are not always insanely cybered killing machines (Tiger M notwithstanding), yet if you want to get to them, you have to cut through a battalion of trained guards, same way shedim should have followers and supporters who'd die in their place.

I used a Shedim-like character once. (I let it open if it was one, or if it was something from BEYOND)

Possessed a tiny young elf sorceress (after luring, baiting and corrupting her through a lesser artifact). I gave it all powers of a shedim master with a handful of initiations. But had it "only" have a force of 6 and severe drawback (needed a ritual a day to stay in the world. Host body was deteriorating a bit etc.)

She gained a covert "research-grant" from a Tir na Nog house, gathered "research assistants" and taught them (all mages) a corrupted meta-techniques (which they thought would bind the background power of ley-lines to theirs to act as power-foci). But in reality it would bind them all together, so when in the great ritual they all DIED, the shedim would have acces to ALL those bound places, filled with the energy of all those deaths, FINALY getting enough power to be TRULY here.

And one of these mages was a npc-friend of one of my players. That was the hook.

Those THINGS have plans... they are cunning. This shedim had hidden ressources (A strike-team of lesser shedim and a controlled infected. Also conditioned elements in the groups of diciples (while others were just clueless).

My players took her down though (Even if it was funny when the melee-adept KICKED her into a wall with 12P damage - as the first starting attack- And the 45 kg thin elvish woman just looked at him with a grimace. I rolled no dice and said: no damage. Look on the players faces: priceless. After that, she just said to the samurai: YOU... kill her. Pointing at the face. And he had to do it.

Well, but my mage and the melee adept took her apart in that round though. You can only reflect so much, and roll only so much edge in dodging.

But will she come back? MUHAHAHAHA. It's not like you could REALLY kill them without a trip to a metaplane.

Shedim are in Threats and Master Shedim are in Threats 2, they are creepy and are a pain to get rid of.

I have a theory that the anonymous poster on Jackpoint is a master shedim possessing a Decker that died during the crash, possibly Captain Chaos.

Fun with Free/Ally Spirits!
Blood and Toxic and Insect, Oh My!

These may help you with some ideas.

While shedim should be powerful prime runner material, I don't think their threat should ever be in their combat prowess. The nice shedim find a way to completely destroy a persons life, breaking it down bit by bit. The evil ones take control of of someone important and go that on a large scale.