well I for one still had this dragon idea of a dragon having been forced to breed with, lets say an angel or a elf, resulting in a child

but lets come with a different one, an Elemental
a creature made of living sentient elemental matter
they generally have 2 shapes, the human shape where they are basically the embodiment of their element, able to shift their shape and control the element and other perks
each element would also have a different special trait in human shape
HOWEVER they can if they want to, give up on their human shape, turning into a pure element made creature, each with a different shape, they lose the special human shape trait but gain other abilities fitting their new shape, BUT this is a permanent change and they often end up being more animal like as well, living and traveling around the world, never again fitting into normal lives and so on
only reason why some elementals would do this can be the fact that they stop aging, becoming immortal and gaining huge power, but losing their humanity for ever.
a choice between power and life vs humanity and loved ones

its just a small setup idea, can be changed here and there, but what do you think?
I would create one of these of accepted (perhaps 2 even)
btw, they are supposed to be very rare races and often seen as myth's in this world (trough they do exist)