So as you may have noticed I really like Twilight Sparkle and making her badass. My favourite form of her is darker, more powerful and somewhat gloomy. Here though she has a smirk on her face due to seeing certain things…
Anyways, in my rendition she studied dark magic to defeat her enemies, which tainted her forever and even changed her cutie mark.
Her wings now have dragon-like thumbs with claws. I actually find it interesting to pay attention to the wing shapes of flying creatures in Equestria: Rainbow Dash would probably have falcon-like wings for maximum speed which I don’t find suitable for Twilight, but at the same time she may not seem as grand and magnificent as bigger and older alicorns who are bound to have great eagle wings (or swan wings - for the memes) for long gliding flight. So I chose a middle ground of giving her hawk wings perfect for agile flight.

Now the main obvious difference with the original is that Twi here has blackened legs and feather tips. This along with feathers being slightly damaged was intended to deliver a feeling of raggedness, even perhaps dirtiness, like she was flying close to some black substance and drabbled her wings tips in it and couldn’t shake it off, like her body being through hardship, misery, struggle and injuries: she used to fight, used to be singed by close misses of enemies’ spells exploding, she wears these scars of past struggle which didn’t left her without consequences slightly diminishing her from being in a peak form… Though don’t be mistaken: this Twilight is much more dangerous and experienced, she is used to dire situations and she knows that sometimes cruel things had to be done…

Twi here (like some isekai characters in certain fanfics) wears a sign of the illness or ailment of Sombra’s curse which slowly spreads from her blackened legs transforming her into a completely shadow being.
Legs in principle are an important part of making her look scarred with some non-disappearing traces of injuries or effects as if she maybe even feels some pain every time she touches floor with her hooves (I don’t think this happens, but I like the idea of a constant overcoming of suffering). For me it resembles the kind of a notion that maybe she used to have some hellish igneous hooves leaving fiery hooveprints wherever she walked (like Illidan grom Warcraft) as well as having her hooves burned like Morgoth of Tolkien’s Silmarillion from interacting with a bright-shining artifacts, and finally the inspiration was taken from FoE: Project Horizons but instead of having sick legs with deteriorating bones Twilight here got Sombra’s curse as a replacement showing the abnormal state of the limbs and that sooner or later she is doomed to die as a pony though the pony everyone knew to be Twilight Sparkle is already dead. However in this picture perhaps in a rare moment of nostalgia for what she once was Twilie looks as cheerful and happy as before.

Next there is blackened and curved horn which is a more cliche idea of a dark magic usage sign and to my mind it also represents all of the above: she not only was exposed to darkness but also from time to time overused her horn which became black due to frequent burnouts of being at the limit of her strength…
With this attitude a Twilight like her is bound to be in some sort of a dark and tragic anti-hero drama oriented fiction. And I hope finding something good or even write myself. I have ideas after all…
And I apologise for any poor choice of words I might have made here, English is not my native language.