so much good
The "batpony" (technically Sunlight Aversion Syndrome; unicorns with SAS are traditionally "shadhavars" while earth ponies are "pucas") recessive genes only manifest themselves around puberty, remaining latent up until that time. The sudden 'transfiguration' of 'normal' ponies into night-preferring SAS-ponies was for the longest time inexplicable by pony thaumaturgy and therefore resulted in social stigma and alienation. This meant that exhibitors of the SAS gene ended up congregating (or being congregated) in isolated communities where its expression was from then on emphasized and protected while not removing carriers of the gene from the overall population. As such occasional expression and effective banishment continued even after Birdy Bees discovered the thaumascientific explanation for 'transfiguration' in Anno Celestia 873.
By this point, after centuries of stigmatism, SAS-expressing communities had developed vibrant, independent cultures of their own that refused programmatic reintegration into mainstream pony society outside of night-dependent niche duties. Nevertheless, active intervention by the Celestial administration post-AC 873 has by the modern day mostly relegated the stigma to a historical footnote, though 'transfiguration' continues to be a trying event for SAS-expressors and their SAS-carrying families. The return of Princess Luna in AC 1001 resulted in even more Royal support for the SAS community and that, combined with increasing interaction such as the urban 'night life' in Manehattan, appears to be shifting Equestrian society from tolerance towards celebration of SAS as fully accepted and 'legitimate' pony phenotypes.
Hey, she actually looks decent.
Funny how an internet illustrator is better than the 'professionals'.