Dean Winchester, Supernatural Season 9
Pretty sure that this is everyone's favorite iteration of Dean Winchester. Demon Dean only lasted about two episodes but even in that amount of time there was a change in his style of dress that lasted throughout his darker Season 9 arc. Like Will Graham, Dean Winchester is mostly seen in jeans, flannel and hiking boots, reflecting his Midwestern roots. During the darker season however, his shirks all of the above for slimmer, black jeans, leather and darker toned t-shirts. Since he is very firmly not a demon for most of Season 9, this change in costume style seems more so to reflect his darker mood as he deal with the curse on the Mark of Cain. We have to say though, leather jackets definitely look good on this character.
Bonnie Bennett, The Vampire Diaries Season 4 Episode 21
In the first season, it seems like Bonnie is going to be firmly slated in the "best friend" category. But by the fourth season when she begins practicing dark magic, we are pleased to see that she is given a spectacular arc of her own. Previously dressed down in simple thermals and jeans with flawlessly straightened hair, Bonnie tends blend into the background. But by the fourth season, rocking her natural hair and a much darker aesthetic, it's nice to see she has a sassy personality of her own.
Jace Herondale, Shadowhunters Season 3 Episode 8
Some might say that given this character's relatively dark aesthetic even before being possessed by a demon, that there wasn't much that needed to change. But the subtle changes are there. The stubble, the messier hair, the more formal clothing, it's all very much out of character for Jace. Jace is already a pretty dark character to be sure but he is still basically just a boy, barely into his 20s. Before the possession, all of his features and style points to his youth (read: innocence) the demon corruption pushes him farther into adulthood hence the facial hair, longer locks and crisp suits. Still hot though.
Willow Rosenberg, Buffy The Vampire Slayer
The ultimate villainous transition! Willow has gone dark a few times over the course of Buffy The Vampire Slayer, but the best was when the characters were shown the alternate timeline where Willow was actually a vampire! Willow is the ultimate in geek sheep, with her sweaters, overalls and mostly bland apparel. Her vampire alter ego on the other hand seems to be a fan of corsets in shades of red and black. I don't think we need to go too much into detail on what the difference in costuming represents.
Cristal Flores, Dynasty Season 1 Episode 1
By episode 8 we have discovered that sweet little Cristal Flores has a secret name, a secret past, and a secret family. Some might say that Fallon is the villain of this story but we all know that a secret bitch is a lot scarier than someone who is bitchy outright. Cristal is almost always wearing some form of white, with a come hither detailing to it. Whether it is a plunging neckline or a slit up the side, her costuming reflects her secretive nature.
Mona Vanderwall, Pretty little Liars Season 1 Episode 1
Did we ever find out who A actually was? How many A's were there exactly? Was anything in this show ever actually explained? There was so much back and forth throughout the run of this show that it's nearly impossible to even come up with a coherent synopsis for what the show was about. However, one character whose antagonistic nature seemed to be pretty stable, even when she was helping out one of the main characters, was the character of Mona Vanderwall. The geek girl, turned sexy mean girl was one of the most fun characters to follow throughout the run of the show. In flashbacks, she is often shown in childish attire, glasses and pigtails, representing her innocence at that point in time. In the main time line however, with her blood red lips, cat eyes and darker color palette, her questionable morality is clear. Ladies and gentleman, never trust a girl with blood red lips.