And here is Frenemy Dusk, my version of evil Twilight.

She was the biggest challenge out of her and Cadance (aka Heart Attack), mainly because of her concept. She is the princess of friendship and I tried to look for ways of taking the concept of friendship and making it dark and evil, kind of like how you do might do with Love/Lust. I figured it out however. She's based around the concept of wrath, and getting revenge on those whom you were once friends with, and trusted.

LORE:

After resigning as Twilight's royal advisor due to her questionable and even tyrannical choices as ruler of Equestria, Spike returned to Ponyville and formed a rebellion to dethrone her before she could cause more harm. Upon learning that her once closest friends were conspiring against her, Twilight felt betrayed and sought revenge. As many ongoing battles erupted throughout the kingdom, Twilight became consumed with wrath and transformed into Frenemy Dusk, with the ultimate goal of retaining the throne and destroying all of those who betrayed her. Eventually, Spike was able to defeat her by draining her magic using the staff of Sacanas, and banishing her into the heavens similar to how Celestia banished Nightmare Moon. She has been banished ever since and Spike became Equestria's new ruler alongside Sweetie Belle.

But it is prophesized, however, that she may return one day as a constellation of stars in the sky are a constant reminder of her presence. She waits patiently beyond the far reaches of the universe, ready to take her vengeance.