"Hero goes evil storylines" are fairly common in comics. Everyone has one or two, and they're okay provided they don't seep into the collective consciousness of the potential creator's pool as genuine characterization. That's usually not a problem provided it's acknowledged in the narrative as strange behavior, confined to a single storyline in a single book and not spread out over two company-wide crossovers, five writers and eight years... *Ahem*. Not that I mean anybody specific or their twin brother.
Still, even if a writer keeps it in the series, wraps it up at the end and explains it away neatly as the plot of such-and-such-villain there's still some seriously irritating trends with "Hero goes evil storylines", and no small concern is the tendency of artists to take advantage of an excuse to "slut up" an otherwise sensibly dressed female character and dress her in a ridiculously sexualized skimpy and cutaway costume. Off the top of my head I can remember this shit happening to the Invisible Woman, Linda Danvers Supergirl (admittedly those vented jeans looked pretty stylish and I liked the jacket a lot), Kara Zor-el Supergirl (which took some doing in comparison to the outfit they'd had her in before), Mary Marvel, the female heroes in Final Crisis who'd been converted to Female Furies (I don't remember if Wonder Woman was attached to that or not, but I liked that her anti-life version was just her normal look with a really ugly beastmask), Jade, and Polaris (really, anyone who's been possessed by Malice).
Strangely, most (but not all) possessed men prefer adding armor, new capes and dark masks to discarding unnecessary articles of clothing. I'm sure there's some complex analysis in the way male and female sexuality are differently repressed, but I suspect that the high incidence in mind control/possession storylines on female characters dressing like strippers over male characters exploring deeply repressed homosexual urges invalidates it.
Anyway, there are a couple female heroes that get to put more clothes on whenever they get a "Suddenly a Bad Girl" plot and interestingly enough they're both from Silver Age X-Men. They go from minidresses and swimsuits to full body suits.
Of course, everyone's familiar with Jean Grey's iconic "Dark Phoenix" look. Only an idiot would mess with the sincere "oh shit" reaction characters get from seeing Jean (or any of the Xerox Jeans in the Marvel Universe) decked out in red and gold. Interestingly enough, of course, after the first sash and leggings costume she never went back to the minidress. That's the power of proper fashion.
Even by Silver Age standards (where she started as a villainess but not an Evil Villainess), Wanda Maximoff always dressed a little skimpy with some pink nylon at best. She's usually in a red one-piece with pink nylons, but she ran around in a loincloth and a halter top in the 90s. But when she goes bad, she pulls out the winterwear. Check out Darker than Scarlet's look. She's got full sleeves, a more covering cloak and long pants.
Avengers Disassembled: Draping her cloak around her.
Later on, when injured she appears to have changed from nylons to pants but that may just be her thigh-high boots. They caught her by surprise in this one, though.
House of M: A long baggy gown. (The Civil War mini also has her in a long gown, in drastic contrast to Lorna's dayclothes.)
Children's Crusade: Medieval Chic.
She's more well-meaning and misguided in House of M, and I suspect that's what Heinberg's going for with this Doom thing so maybe in addition to the Long Pants of Evil we have the Long Skirt of Delusion. Either way, if she's wearing more than the Nylons of Virtue we're in trouble.
The most interesting, though, is the Possessed by Elder God Chthon outfit from Nights of Wundagore:
This isn't interesting because it's unlike Wanda, in fact it probably sets the trend of off-the-shoulder cape, mild cleavage (especially compared to her good girl look) and of course the Long Pants of Evil that come with all of her bad girl outfits. What makes it really interesting is Chthon as an entity is not opposed to showing extra skin. How do we know? Check out Possessed By Chthon Quicksilver:
Granted, he is also wearing long pants. That might be the thing.