Just wandered over from the MW realm with a few comments about Preta and *mancers.
On Preta, even with frequency dialed down, they still kill forts, just a little slower. I was totally safe for the first 3 or so years of the fort, but after opening the 2nd cavern, I started getting a death a week or so. I would get a So-and-So possessed, and then they would either berserk and be put down, or suffocate. So far just those 2 things, but its literally one guy a week, and there is no way to block or protect against them that I can see.
Unstopable random killers are kinda awful. The idea is neat, but there has to be some way to block or kill them, or they just hop from guy to guy, systematically wiping everyone out.
On the *mancers...
I was the dropping stuff report person. The dead walk events are constant, the whatevers they are arrive, promply drop all of their gear, and they are freaking loaded up when they arrive, and then get slaughtered by any old random wildlife. It is understandable that animate enchanted wine may not be physically threatening, but its to the point where I watched a passing family of camels slaughter 20+ mudmen with only a few losses.
Also, after killing them, each of their corpses, or what functions as corpses, gets up and starts moving around, but is friendly. Eventually your fort gets completely swarmed in friendly "undead Mudmen left hand" and other such things. You can order your military to kill them and weapon traps will keep them out of the fort proper, but even so, they probably shouldn't be doing this.