Inspired by the wonderful series over at Lurking Rythmically, I thought I'd type out a few words about dragons on the Coin. They're not hugely different from "standard" D&D style dragons, except where they are...
Dragons breath fire.
Of course, there's quite a bit of variation as to how they do it. Some create a high-pressure gout of flame a hundred meters long, some spit fireballs that explode, some squirt flaming liquid, and some exhale clouds of smog that they then ignite with an electrical discharge. So, while fireproof armour will be invaluable against any dragon, the fire delivery method it has can change other tactical decisions.
Occasionally something will go wrong with the internal furnace of a dragon, usually while it's growing up, causing it to exhale toxic sludge or blasts of lightning. Other dragons consider such creatures hideous degenerates and try to kill them wherever possible.
Dragons are NOT immune to fire.
Dragonhide is very tough, turning aside most weapons, and it is also magic-resistant, turning away a fair number of spells. But, while it is quite resistant to heat, it is not totally fireproof, so a dragon can wade through a burning building, but will still be hurt by the breath of a fellow dragon. Or a large pile of explosives.
Most Dragons LOATH water.
Possibly this might have something to do with the fact they're creatures of fire. Or possibly they just don't like getting water under their scales. Either way, they avoid getting wet whenever they can. This is, in fact, why most dragons have their lairs in caves or dungeons rather than places open to the sky - while being able to fly straight up would be a huge tactical advantage, no dragon is going to sleep somewhere he might get rained on.
Having said that, they're not allergic to it or anything. In fact, if a dragon can overcome it's dislike of the substance, their sleek shape, huge lungs, and vast strength make them excellent swimmers.
Their life-cycle is very uneven.
It takes a dragon only a month or two to grow from a two-foot-long hatchling to a small-house-sized monstrosity, a period during which they are constantly hungry, and will eat literally anything in their immediate vicinity that they can chew (which, considering how hard their teeth are, is basically anything at all). However, once they reach that size, they grow very slowly. As they age, they get bigger, smarter, and lazier. Thankfully for the people of the Coin, once they reach a certain size, the dragon's internal systems seem to become self-sustaining, and they refuse to actually wake up for anything less than a direct attack on their person.
They're Magical, but can't do magic
Dragons are very magical. That's why they can fly despite their weight, can breath fire, can grow scales as hard as steel, and so on. It's also why they have such a huge variation in physical construction within the one species. But, like most inherently magical species, they can't actually cast spells like a human wizard (in fact, it might actually be humanity's lack of inherent magic that lets them do that, but that's a theory for another day). They certainly cannot change shape at will.