She was determined to exact revenge. She began studying dark magic, curses and plagues ever since, finding one to exact her revenge on Twilight Sparkle and prove that she’s the superior sorceress. During her studies, she meets a dark figure willing to help her exact her revenge…
The mysterious pony elaborated how his aid could reek her vengeance on Twilight in every way she planned to; to publicly humiliate her, force her into exile herself and, in her shame, end up with the same fate Trixie would endure.
Tempted by the offer, Trixie asked what she would do in return… The figure smiled, promising that his assistance would be reward enough.
Trixie hesitantly agrees, still considering the variables here – but before she could come to any conclusion, the figure turned his rump at her, extending his skunk-like tail in plain sight and sprayed her with a horrible odor even a skunk couldn’t endure.
Trixie hacked, coughed and cried out in terror, before passing out from the horrible smell she now wore. When she awoke, she discovers she’s been transformed… Her rear end felt different, her insides ached, and without much delay she realized that her coat and mane have been cursed to a natural monochrome hue… She saw a distinct white stripe on her tail, she immediately recognized as a skunk.
The figure was gone, but his odor lingered heavily… But much to Trixie’s surprise, the smell was thoroughly bearable, despite smelling it with the same potency as before. She shed a single tear, but then boldly overcame the penance. She been granted the new life, a sentiment she’s been hoping for, and a new chance to quench her desire for revenge against Twilight Sparkle…