Posted something like this some time ago, wanted to see what people have come up with since. Basically, just list your cool syndrome-based modding ideas.
This has a sister thread in suggestions,
http://www.bay12forums.com/smf/index.php?topic=61477.0 , where we ask for things we need Toady's help for.
Topics divided for length. Please submit your own ideas, or confirm if the ones listed here will actually work.
Syndrome-Rich Enemies
Living Bombs- have blood that boils at room temperature, with an attached syndrome. A dwarf (or other) cuts one, it explodes in a cloud of poison gas. I'm thinking either light bleeding or heavy necrosis for the effect- it will instant-rot any enemy who attacks it, dying in the process, or release a gas that causes everything nearby to bleed, setting off a chain reaction. Would be fun to make them pets... maybe give them *really* valuable milk, so you want a lot of them, but god help you if a goblin cuts even one of them...
Vengeful Bones- not sure if you can do this, but make their bones, or something else that only really exists after the bodies have rotted, boil at room temperature and release a nasty effect. You can fight and kill them safely, but god help you if you don't clean up the bodies...
Sub-Zero Suicide Bombers- usable only on glacial maps. Their entire bodies explode into a toxic gas at room temperature; fortunately, they only exist on glaciers. Sadly, they will do anything they can to get into your base.
Seeker Swarms- something flying with the breeding rate of a cat, barely any attack and a paralyzing bite. Highly aggresive. Highly valuable if you can catch them. For an additional twist, give them two life stages, if possible- the children swarm and bite, the adults are immobile, and possibly killed by a gas released by their young, resulting in a gestation cycle where the adults essentially are egg sacks for swarms of the young.
Syndromes for Combat
Unseeing-eye dog- Very useful pet. Has a trailing gas that causes instant eye necrosis on any non-dwarves, non-unseeing-eye dogs. Give them to your champions to give them an edge, or your broker to get back at the elves.
Ice Lab Bombs- make a custom reaction that creates a material that boils at room temperature, with a syndrome- use only on glacial maps. Build the labs and storage high in the glacier, where it's cold, and have the entrance to your base fun many z-levels down, and preferably go over some magma. Have the storage yards next to a vertical shaft leading to the killing zone, then just designate the material to be dumped when invaders come.
Magma-Activated Bomb- not sure if this works, but keep 1x1 pools of magma at significant points (killing fields, trade depots), and make a material that boils in magma to release a deadly gas. Then use dumping to trigger the burst. Alternatively, no promises if this works, use drawbridges to fire them into a magma waterfall.
Decontamination Airlock- make a creature that breathes a gas deadly to all non-dwarves, and keep them as pets on either side of a corridor with fortification walls. If any elf tries to sneak in, they get melted.
Syndrom Gimmicks
Contaminated Surface- make Rhesus Macaques or something similar have a gas effect that causes them to bleed out, and blood that is death to dwarves. Result? A surface soaked in blood, which will spread through your fortress if proper quarantine is not observed. Recommend scrubbing all migrants and traders with lava.
Health Code Enforcement- not sure if you can do this, but edit dwarf blood and vomit to have mild syndromes for necrosis and or naseua. Result? One person starts throwing up, clean it up fast or your entire fortress will drown in vomit.
Chain-Exploding Dwarves- make dwarven blood boil boil at room temperature, and cause dwarves to bleed. Whee!
Syndrome Mechanical Tricks
Spider Plague- thanks to one of you for this. Make a web-spinning vermin whose webs boil at room temperature and are posion if inhaled. Makes cats useful. Alternatively, make the posion only effect cats.
Disease Approximation- this one is hard to replicate, but a lot of people have reported seeing blood getting tracked around acting like a contagious disease. Closest thing we have to dwarven pandemic.
Paired Beasties: Make one creature whose blood is terribly, terribly nasty, but has adamantine skin, and is almost impossible to make bleed. Make another creature whose syndrome causes the first creature to bleed. Mix and enjoy.