Ok, two more things I'd like to figure out how to do:
1. Apply a syndrome to dwarves when they're above ground outside.
I thought I might attach it to above-ground plants and grass? Maybe a syndrome-inducing interaction triggered on grass trample? (Can I set grass's trample threshold really low and make it's regeneration rate very high?)
Or maybe have a certain syndrome-inducing plant part on trees and above-ground plants that explosively boils? (And regrows quickly?)
Is there a way I can use evil rain for this? Like force world gen params to make only evil regions, then use the raws to force a specific flavor of evil rain? (i.e. only make evil rain that applies this specific syndrome?).
Or perhaps instead of a syndrome applying outside, I could have a permanent or frequently-occurring syndrome that sets all dwarves' cave adaptation super high, making them immediately vomit whenever they go outside?
2. Force dwarves passing through an area to acquire a syndrome
This plays into my last question, as I want a way to apply a syndrome that is the "vaccine" to the "going outside is awful" syndrome. Could this take the form of a custom building with an action required in order to pass through? Maybe a workshop with all blocked tiles and one reaction, a reaction that applies both the desired syndrome to the dwarf and a different syndrome to the workshop itself to temporarily change its body to a different workshop with all unblocked tiles? Sort of a locked door that needs to be manually unlocked each time.
What about a restrained or pastured custom animal that uses an interaction to apply the syndrome to anything walking near it? Maybe a weapon trap, triggered by dwarves, that contains a syndrome-applying weapon? Can pressure plates cause syndromes?
(Sorry I'm just brainstorming out loud here; I'm really new to modding (and DF generally) and don't quite have a grasp on what things are possible)