In my world I have a race of god-like beings who I've recently decided should be shapeshifters. However everything in my world comes in threes, and there are three races / clans of these beings. For comparison a related branch of beings is mortals; humans, elves and dwarves.
The main difference between these clans in my mind is each has an affinity with a different branch of magic, but I want there to be something else that sets them apart from each other. Something that makes an individual of Race A have more in common with another individual of Race A than of Race B or C.
There are some limitations that have ruled out some of the more obvious options though;
- These god-like beings are practically wiped out (by forces of nature / other god-like beings) and the survivors live largely in secret. This is one of the reasons I want them to shapeshift. So whatever feature sets them apart from each other shouldn't stop them from looking like a human, elf or dwarf. So I can't just say Race A can take any form but their skin and hair will always be blue or something similar.
- They can inter breed with each other, and with the mortal races. Kind of already covered by being able to blend in with them, but they should be able to take and maintain a humanoid form that could reliable breed with each other and other humanoids. It's also not strictly necessary but if their defining feature also allowed you to identify hybrids between the races that would help too.
The beings themselves are very powerful mages and immortal (Tolkien sense, as in live forever but can be killed) if that matters.
As for their shapeshifting my explanation is that they can modify their bodies to suit their environments in the way that mortals modify the environment to suit them. So instead of wearing clothes or building buildings to make a place more hospitable they change their bodies (though they will adapt clothing and buildings from mortals, they just don't need them in the same way). They can change their whole bodies or just adapt them (so they could grow horns, feathers, scales etc. not sure if they can grow extra limbs but I'll probably allow wings so I can't see a reason not to) and while they may have a 'true' form I don't think it is something any of them would use frequently as they instead adapt and change their bodies to suit their whims and personality.
So how can races of shapeshifters have some kind of defining features which set them apart but don't interfere with their ability to shapeshift?