Here’s an updated Ember design because the last time I drew her (below) was a little over a year ago! As always, she continues to get more dragon-y every time I draw her
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Dragons have enlarged chests that hold flammable helium, both to make them lighter during flight, and to trigger fire creation. This also makes it so that they can’t sink in water
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Dragons have long, thick tails that are very sturdy and elastic. Most dragons can sit on their tails as if it were an extra limb. While some dragons have tail flaps, they are not needed for flight. The tail’s primary purpose is balance.
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Dragons grow indeterminately, which means they never stop growing larger. Ember here is about 5 stories tall, and she’ll keep getting leaner and bigger. If she were on all fours, a horse (or mlp pony) would reach her chest. For scale, a human would be about as tall as her knees. For extra scale, she’s about double the size of the above drawing.
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Dragons grow very quickly at first, from the size of a pillow to the size of a house in about 20 years. After this, they keep growing, but much slower.
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Dragons’ front claws mimic paws in that they’re basically hands
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A dragon’s wings must reach from their shoulder to at least their thighs in order for flight to be possible. Ember’s wings extend to her tail.
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Dragons have a limited supply of fire. It’s quite a lot, but can be used up. If it is, that means all the gas in their chest has been depleted, making flight difficult or impossible.
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While dragons can’t sink, they also can’t swim very well due to the size of their wings.
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Dragons that live to be colossal tend to die not by natural causes, but by their own weight.
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There are dragon species for each of the four elements, with the most common by far being fire dragons.
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Dragon fire is not limited to the color red. It can be blue, white, or anything else, but red is the default, per se. Typically, a dragon’s fire color will match their eyes, but this isn’t always the case.
Not sure about the “internal gas balloons for lift” idea. Her chest isn’t big enough for the kind of balloons you’d need to lift something that weighs as much as a 5 story lizard would. That would probably look like a small blimp.
Using that gas for fuel also presents the problem that it would have to be kept under a lot of pressure to generate enough fuel for a flamethrower style breath attack that would be expected of a dragon. Would likely work better with a biological equivalent of napalm, that can be stores as liquid and sprayed, like a traditional flamethrower.
If you want different color fire, all you’d need with the liquid fueled fire, is to add the right elements to the fuel. It would likely be a matter of the dragons diet containing those elements.
Edited