Howdy there. Just wondering if there's any way of getting a Walking Dead type of world? By which I mean almost everywhere is populated by undead. I don't know what parameters affect tower generation, but maybe making most of the world squares evil would do the trick? I'd be happy with a smaller or small sized world. Anyone got any advice?
There's a few different types of undead. At least:
Thralling from evil clouds.
Reanimation after death.
Controlled/created by a necromancer.
Part of the region.
If you're looking for a fortress mode embark that has both reanimation and animated arriving corpses/undead wild animals,
this one qualifies.
What features are applied to evil biomes or regions or what effects/syndromes come from particular evil clouds or rain is procedurally generated.
You can, for example, generate a world that has lethal versions of all of those, while some are minor inconveniences at best.
While towers are a source of undead, the denizens, at least, from what I've seen, stay in or near the tower unless on a specific task. That may be different with the new towers that spread evil in Adventure Mode, but I haven't tested enough of that personally to speak with any authority.
From your request, it seems like a biome (or many) where the trees and animals are all undead/dead is likely the closest match. I call these animated corpse embarks, because you get things like Barn Owl Corpse, Echidna Corpse, or Buzzard Man Corpse arriving on the embark regularly. (depending on the biome)
It's worth noting, though, that in these embark regions? Surface existence is extremely challenging without your military being fully equipped in metal gear and having very high military/combat skills. At least, in fortress mode. Particularly if you start getting Undead versions of Giant creatures.
The other challenge is that Regional Interactions (which are the things that can have/cause these reanimating, corpsing, etc effects) are only different based on different regions. If you have one region throughout your entire world, or only a handful, you'll only get a handful of unique Regional Interactions, and thusly, very few chances at seeing Undead regional effects within range of other features you may desire, like water, metal, sand, clay, flux, or trade with other races. Generating unique regions can also be tricky, depending on what biomes you're comfortable with or desire. It's much easier to create very large single regions rather than many tens/hundreds of tiny regions, which is the opposite of what you want, in this scenario.
Obviously, it's
possible to get it all together. However, it can take some time reviewing many tens/hundreds of worlds, depending on how specific you are with your requirements, and how few or many unique regions there are in the target worlds. Evil clouds are similar. You can have many evil clouds in a world, but there's often no guarantee they have the evil that you want, or even that they'll show up with enough frequency to make it challenging, although one brief mistake can end your fort very quickly (if all your dwarves are above ground and all are caught in a cloud at the same time)
Lastly, there are now quite a range of different necromancer undead types. Experiments, lieutenants, divination, ghouls, summons all create quite a range of type, difficulty and density.
Recently, for example, I had an unexpected visit from some necromancers who brought many crossbow/bow/ranged attackers. Hadn't seen that before, personally, and it .. wiped out the fort quite handily. There's also demonic experiments permitted as well, which.. given how simply LARGE demons are, and the consequences in combat, any undead version would be very very difficult to engage hand-to-hand.