Almundra, the Ideastar.
 
She was once a star that had chosen to leave her place in the Hyperborean heavens, like many before her, becoming a pegasus-like spirit known as an Asteri. They differ from regular pegasus mares by their tall, thin stature, their large wings, and great beauty, as well as their iridescent/pearly coats and the occasional Asteri having silvery ‘swirl’ markings. Their magic is powerful and ancient, far surpassing that of even a mortal unicorn, and the stars (and by extension, Asteri) are comprised entirely of primordial black magic.
 
Almundra was a star that fell because she’d fallen in love.