I need to find that ability about not needing Fort saves to avoid nonlethal damage in cold weather...
Well, we could easily write it again, but I guess we'd like the same name.
We probably need a magical flight ability, like the beholder.
You know, the SRD/MM doesn't do a good job separating which critters have magical or non-magical flight... Should we just state in the flavor text that its flight is magical?
What to make of all that?
Probably flavor text for the potion ingredients.
For the armor, I suggest the following sidebar (modified from dragonhide):
Haundar armor: Armorsmiths can work with the armor plates of a haundar to produce armor or shields of masterwork quality. One Gargantuan haundar provides enough armor to produce a suit of masterwork armor for a Huge creature. By selecting only choice scales and bits of hide, an armorsmith can produce one suit of masterwork banded mail for a Large creature, or one suit of masterwork half-plate for a Medium creature, or one masterwork breastplate or suit of full plate for a Small creature. (Multiple haundars can be used to create armor for larger creatures.) In each case, enough hide is available to produce a small or large masterwork shield in addition to the armor.
Because haundar armor isn’t made of metal, druids can wear it without penalty.
Haundar armor costs double what masterwork armor of that type ordinarily costs, but it takes no longer to make than ordinary armor of that type. It weighs half as much as the corresponding type of metal armor.
Haundar armor has 10 hit points per inch of thickness and hardness 7.
(I made it not as hard as dragonhide.)
Speaking of haundar armor, do we want to put in the unarmored "soft spots"?