Mirror universes. There are many stories of them, some where there is slight change, other times where there are complete 180's in the personality of friends.
But they are all true.
Because in the ones where a good person becomes evil, they do not become more powerful, or even gain anymore power than their good counter part can ever gain. Rather, they're completely balanced.
Take for example the four mutant turtles I have come to call my sons.
Michelangelo is the heart of the team. As long as he smiles, the others can go on. A bit of a goofball, but he means well.
But look at him through the mirror of evil, and you'd see someone angry, not holding back his knowledge and harming friend and foe alike . . . to compare him to something considered evil or bad, try the horseman of the apocalypse famine. Knowing what is considered pleasurable to others, and taking it away.
But here, in this reality, he is too kindhearted to imagine evil, which is good.
Donatello might be a better example, the brains of the team. His own knowledge is used to help his brothers, and make sure they stay in one piece.
Now look at him in the context of evil . . . of the apocalypse horseman Pestilence. His knowledge of chemicals, poisons and other things could have him creating horrible things . . . to disarm a bomb, you have to know how to put one together, and all that.
Raphael . . . a stubborn and rash young turtle. His solution to things is bashing them, God knows how many times Donatello's repaired the tv remote from Raphael's frustration when the battery runs dry, and he doesn't check.
The Horseman War would be a correct correlation. Fighting just because he can, a berserker at best. Letting his anger rule him, rather than attempt to control it. He loves his brothers, and that helps, but without it . . . I shudder to think what would happen.
And finally, Leonardo. He is the eldest, and the protector of his brothers, he'd get in between them and a killing blow. He's better at stealth than his brothers, though Raphael has better strength.
He is Death. Killing so silently and quickly enemies wouldn't have a chance. A ruthless and emotionless killer. I shudder to think of what would happen if they ever met a truly evil Leonardo . . . only one of the two could live from that fight.
I highly doubt only one of my sons would become permanently evil . . . There would be the other three, to pull the one back from the edge, with the help of Ms. O'Neil and Mr. Jones. What I do fear, is if they fail in that, that they will all fall into darkness . . . a package deal, so to speak.
If Michelangelo fell, he would take away the light and hope his brothers cling too. He'd be bait for a trap that they would walk into. If he chose to, he could probably kill Raphael or Leonardo, neither of them could truly hurt him, even if he was evil.
Donatello would take away the medical attention and information that his brothers need. Even with April's help, they'd still need their own brother's reassurance. Bait for a trap, and probably would use that against them, reeling them in.
Raphael would take away the strength, and the voice of blunt truth. Casey Jones could temporarily hold that, but it would not be their red banded brother. And like Michelangelo and Donatello, the ones that tried to remain good may still fall . . . but I fear that Raphael would kill Leonardo first, capturing and holding Michelangelo until Donatello came to him.
And if Leonardo fell into darkness, he would take away the protection that they all need. I am old, and could only keep the remaining three together for so long, before I would die and they would fall, wishing for their elder brother's protection once more, like children who need guidance. Raphael could not oppose him for long, not that he is unskilled, but because that, while he won't speak of it, he truly cares for the elder.
If two were to fall, there would be an impasse for a while, until the scales tipped in either direction. And if three were to fall, the last would not be able to resist the pull of his brothers.
My sons are all firmly rooted in good, but evil can sometimes, oh so slowly, take hold of a person's inner heart, slowly spreading until they realize to late what they've become. Hopefully, the fears and musings of one old rat will never come to pass.
There, Ninja Turtle fic, that's plot bunny was driving me crazy. Review with any questions, and I hope you enjoyed it. (Michelangelo is the one turtle I have a hard time seeing as ever going completely evil. Mostly, it's either Leo, Raph or Don that get into trouble on that level. But I've noticed in all the stories, as far evil as one will go, the other three always seem to be able to pull them back.)