Dragonkin exist in all climates, from volcanoes to arctic wastes. Traditional biology doesn't really apply.
Like dragons, dragonborn were often mistaken for reptiles, but were in fact warm-blooded draconic creatures. In fact, the internal body temperature of the dragonborn was warmer than that of most similar races, being so hot as to seem feverish to the human touch. While this might seem disadvantageous, the lack of hair and large mouth allowed the dragonborn to displace body heat at an effective rate, meaning dragonborn were comfortable in cold climates while remaining no more vulnerable to heat than humans.
So I'm wondering if they are cold blooded, warm blooded or monstrous physiologically? Is there established lore?
[Foreigner starts playing]Hot blooded!
(https://forgottenrealms.fandom.com/wiki/Dragonborn)
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Short story: they're magic.
Dragonkin exist in all climates, from volcanoes to arctic wastes. Traditional biology doesn't really apply.
They're a terribly patronizing alternative for players who actually want to play dragons...