You can use iron wool (is that the name?) as leather I think.
It's fleece. Can be made at magic loom.
As for syndromes, here is what I figured out.
[SYNDROME]
[SYN_NAME:rainbow gas inhalation]
[SYN_AFFECTED_CLASS:GENERAL_POISON]
[SYN_IMMUNE_CLASS:PEGASUS]
[SYN_IMMUNE_CLASS:PRINCESS]
[SYN_INHALED]
[CE_UNCONSCIOUSNESS:SEV:10000:PROB:100:START:0:END:3600]
[CE_DIZZINESS:SEV:30:PROB:100:START:1:PEAK:50:END:12000]
[CE_DROWSINESS:SEV:40:PROB:100:START:1:PEAK:50:END:12000]
[CE_IMPAIR_FUNCTION:SEV:1000:PROB:100:BP:BY_TYPE:GRASP:ALL:START:1:PEAK:50:END:8400]
[CE_SPEED_CHANGE:SPEED_PERC:50:RESISTABLE:START:1:PEAK:50:END:12000]
I don't even know, why it looks so strange in this code...
Anyway, this is the syndrome itself. Unconsciousness for three days, dizziness, drowsiness and speed cut by half(I still think) for ten days. All counted from the moment of exposure. I am uncertain whether or not staying unconscious near the source of gas prolongs the issue. I suddenly found myself lacking time to do anything in terms of testing. I am sorry, for I said I would test...
I would say impaired grasp for a week, but that doesn't work for some reason... that, or it is not listed on health screen.
Though this will work as intended only if you go to creature_pony_pony_NEW.txt, go here:
[BODY:QUADRUPED_PONY:PONY_TAIL:2EYES:2EARS:2WINGS:2LUNGS:HEART:PONY_GUTS:PONY_ORGANS:PONY_JOINTS:THROAT:NECK:PONY_SPINE:BRAIN:TONGUE:SKULL:PONY_MOUTH:TEETH:RIBCAGE:EYELIDS:CHEEKS]
[CASTE_TILE:'p']
[CASTE_SOLDIER_TILE:'P']
[DESCRIPTION:A pony with beautiful wings.]
[CASTE_NAME:pegasus pony:pegasus ponies:pegasus pony]
[BABYNAME:newborn pegasus foal:newborn pegasus foals]
[CHILDNAME:pegasus foal:pegasus foals]
[FLIER]
[SPEED:777]
[MAXAGE:75:120]
[POP_RATIO:100000]
and add
[CREATURE_CLASS:PEGASUS]
tag somewhere there. This will render all pegasi immune to the syndrome. And because all alicorns are princesses, that's already covered.
Now you have to go to inorganic_rainbow.txt and add the syndrome to every gas color. I was wondering about also adding it to those clouds that are set to boil, but I dunno. Your call.
Feel free to change the numbers and such. If you also know, why grasp is not impaired, please do tell. I would like to know.
Cheers!