In the process of defeating the major obstacle of book 2, one of the protagonists (a female, winged, "angel" type race, who is the quintessential "goodie two-shoes") is essentially "copied" by dark magic, creating an "evil twin" type of character, with an equal but opposite appearance (white wings -> black wings, light pinkish skin -> dark blue/purplish skin, etc) and an "evil" personality instead of a "good" one (obviously the character will be more complex than this, but this is just the idea in a nutshell).

My question, is this too cliche to do, despite how fun it would be to write? I know the rule is you can do anything, if it's done well, but let's assume you as a reader enjoyed the first 2 novels, and then you reach this plot point. Will you go "oooh nifty, now she's got an evil version running around" or will you respond with "wow how cheesy, a bizarro-superman storyarch." The magic that produces this effect is consistent with the magic of my world, so hopefully that isn't an issue, but is this trick just too overdone?

There's not much worse than a long-running series starting to read like the author's pulling ideas from a plot hat at random.

If the evil twin was doing Terrible Unspeakable Things™ without a drive or motive I could relate to, just because she's the main antagonist of the story, I don't know if I'd want to read on.

However, if she reflects on her role as an "evil" twin, and has some sensible motivation towards her actions, I think that would totally give legitimacy and a nice flavor to the plot.

So, in other words - if you take the cookie straight out of the cutter, it wouldn't be something I'd want to read. But if you played with the dough a little, using that initial plot idea as a launching pad, then I think it could be very interesting indeed.

Of course, if you're not planning to polish and send off the manuscript at all, you can do whatever you want. ;)

So - if white angel has an annoying habit of plucking all her eyebrow hairs, black angel should have bushy eyebrows. If white angel is a really good pool player, black angel should be terrible at it (but maybe think she's good.) Play on personality traits too - there are things that white angel does/is like that could be *positives* for black angel. For instance, white angel is sappy and gets taken by every sob story. Black angel is much more cynical, but that cynicism pays off for her in that she avoids being taken advantage of.

I assume your good angel is off on some quest or another. Write the evil twin in a way where she is trying to protect her people against evil thieves. Make it honestly look like the good angel is actually doing criminal acts against society, at least from the society the dark angel lives in.
One could have all sorts of "evil" acts in a society, but still have a code of conduct, rules that everybody lives by to keep a civlization running. The dark angel enforces, believes, and follows those rules.

Opposite doesn't necessarily have to mean one is good and the other is bad. I was thinking of separating the original good angel into essentially her supernatural-like traits vs. her mortal traits. Thus, the "good" version that is left (at least after the developments I've already set down for what separates her humanity from her supernaturality... (it's a word right?)) anyway the good version will probably become much more strict and emotionless, and unwavering so far as breaking the rules to get the job done. In the end, this can be a bad thing. Think if a policeman refused to, say, J-walk or run a red light to catch a murderer because "it's bad to break the law" is taken to the extreme.

On the other hand, this new, dark angel version, instead of being "evil" could simply be more instinctive, impulsive and chaotic. This one, while not necessarily evil, might not have any qualms about breaking societies norms to fulfill her own desires, whether those norms are simple things like dress code and ediquette. Or more severe laws like theft, or murder, etc. Perhaps she has no ability to differentiate between right and wrong whatsoever, even if she does her best to not be "evil" she just can't tell the difference...

So in some sense, the original character that existed really won't anymore. She will have split into alternate aspects of her psyche. The "good" version will be moralistic and conscience-based, while the "evil" version will be primarily egotistical and impulsive.

Wow, now that I've really defined what I was thinking, this would essentially represent a division of this character between Freud's definitions of the id and the superego. Without an ego to balance the two, both can be highly destructive, just in different ways.

Azrael (Who temporarily replaced Batman when Bane snapped his spine) is more of the unknowing villian. He feels completely justified killing innocents if they're in his way, or letting them die to achieve his objective.

The light angel knows the rules, will follow them, will anylize things Her judgement would likely be impared. I would see her harming someone, even accidently, because she cannot logic what emotional damage might be caused. Because she no longer have pride, which is an emotion, she might let her self go slightly, or not be as stylish because it is logical to wear one type of clothing.

The dark angel might be one who explores pleasures, even forbidden ones (she understands the word no, but cannot see a reason to use it....), fly off the handle over little things, get revenge for slights. She would be fashonable and meticulous simply because it makes her feel good to have men ogle her.

If the two fight, it would be one heck of a battle. the logical one would be calculating well ahead of what they were doing to get the emotional one into a bad situation. The emotional one would be unpredictable in her actions, not following logic. Of course, the emotional one could be made angry and attack blindly.

Meanwhile, the superego is essentially the conscience, intent on following all of societies rules of right and wrong. It doesn't let you give in to your desires unless it is "acceptable" to do so, and could thus be seen as the perfect example of logic dictating behavior, utterly controlling ones emotions and desires.