Man, villains are great.
I mean, what's not to love?
They provide constant conflict, drive the plot,
spark at least three unnecessary ship wars each,
not to mention how gosh darn evil they are.
They can be cruel and sadistic if that's your thing,
or working towards what they think is a necessary evil,
or just a sad, misunderstood puppy dog with a truckload of personal trauma --
the possibilities are practically endless.
The only requirement that makes a character a villain is that they oppose the hero,
although, if you want to nitpick, that technically just makes them an antagonist,
but beyond that characteristic, you've got a whole playground of possibility.
But you know what's even better than a villain?
A reformed villain,
because everyone loves a good bad guy,
but everybody really loves a good bad guy.
Not only does it lend credence to the idea that there's a little kernel of goodness in all of us,
but it also lets you take all those great villain-hero dynamics you've previously explored
and protagonist-ify them into some seriously quality banter between your newly expanded posse of heroes.
Now, there are a ton of reasons for villains to turn good,
but they're almost always highly personalized,
because they have to arise from the character of the villain themself.
This is also why the purely cartoonishly evil bad guys rarely get to turn good;
usually they don't have much character behind the villain thing.
In some cases, they turn good and reveal that their cartoonish villainy
had a legitimate character-driven reason behind it,
and become a much more well-rounded character in the process,
but for the most part, Disney Evil is only there to provide evil and opposition to the heroes --
they don't generally get the chance to change their tune.
But a real, well-rounded bad guy can find all kinds of reasons to fight for good:
maybe they realized their villainous motivation was pretty lame compared to the heroes;
maybe they had a fundamental change of heart;
maybe they woke up one morning and realized a military uniform that incorporates a skull
might not belong to the armies of good.
Their mind is your playground, and there are so many possibilities.
Because the trick is, you aren't flipping some morality switch and turning a character from bad to good;
you're arranging for circumstances in which that character will side with your heroes instead of opposing them,
and those circumstances will vary based on the character of the villain, the characters of the hero,
and what circumstances drove them to oppose each other in the first place.
Maybe your villain's misguided and they've been tricked into villainy,
in which case proof of their bosses' malevolence is
liable to be enough to shove them to the side of the heroes.
Maybe they're just won over by the power of friendship.
Maybe their villainous higher-up treats them bad enough that
they have a crisis of morality and side with the good guys just to spite their boss.
Or it could be like a million other things.
Let's take Prince Zuko from Avatar as a good example of the complexities you can dive into.
See, Zuko doesn't technically stop being a bad guy until episode 51 of 61.
That's when he officially decides to join team good guy,
in part because he realizes how screwed up his evil family is,
in part because he re-examines his priorities and what exactly he wants out of his life,
and in part because destiny said so.
Now what makes this interesting is we're basically rooting for him to turn good from episode 3 onward,
which is when we first start to get a sense of how badly the rest of the fire nation treats him.
He's been sent out on a fool's errand to capture the Avatar, someone everyone thinks is dead,
and when it turns out that he's not dead, the entire rest of the fire nation starts doing everything in their power to capture him first,
and Zuko was only doing this because he thinks it'll make his father care about him,
a father who, mind you, spends his first major on-screen appearance burning half of Zuko's face off.
He spends the rest of season one running himself ragged trying to dodge the rest of the fire navy and capture the hero which, you know,
capturing a hero is an objectively bad thing to do,
and then in season two, despite still being an antagonist for the most part,
he officially becomes a fugitive from his own nation,
being hunted by his abusive, sadistic, and sociopathic sister,
who was harboring some pretty crazy favoritism issues of her own.
Now, not only is Zuko a bad guy,
he's the first bad guy we're introduced to, and by far the one with the most intense drive to capture Aang.
Everyone else is basically doing it to spite Zuko.
He's objectively an antagonist, and one of the most persistent ones throughout the series,
but it's really bad for him as a person.
He's in a really bad place for most of the series,
nearly killing himself in the process of trying to scrape up some semblance of love
from his insane awful family. (NOTE: obviously Iroh is not his "insane awful family")
He's angry and unstable, and not in, like, a fun way,
but in a 'somebody get this kid a hug, a nap, a hot meal, and a goddamn friend' sort of way.
In a weird way, we're rooting for both him and Aang, even though their goals are by definition opposed.
But we're rooting for Zuko to figure out that his home life is terrible
and he deserves to have good things happen to him,
and when he finally does, and in the process denounces his terrible father and becomes a hero, it's amazing.
Before that big heel face turn, there are a ton of situations where
Zuko sides with one or more of the good guys.
One notable example involving him actively breaking Aang out of prison very early on.
These temporary pseudo alliances, where they're fighting on the same side
even if they'd be fighting each other at any other time,
are the result of the fact that Zuko's villainous motivation is highly situational.
If anyone else is around to capture Aang,
Zuko is almost more dangerous to that guy than the good guys are.
If not, he's the major threat to the good guys.
He's unquestionably an antagonist to begin with, but his character development leads up to him officially
renouncing his big screwed up family and joining the side of good,
a transition that's almost the end of his character arc.
Whereas in lot of other stories,
getting good-guy stamped on their forehead is step one on the road to anti-villainous character development.
So this is a redemption arc done really, really right.
It naturally arises from the character and his circumstances,
his dynamics with the team are great both before and after he officially joins them,
his goodness doesn't come out of nowhere,
and the traits that made him bad are properly addressed.
Not only that, despite the intervention of his uncle, his decision to become a good guy is just that: his decision.
He doesn't get turned by a heartfelt chat with the heroes where he learned their side of things,
the terrible family doesn't do something extra terrible to push him over the edge.
He basically comes to the conclusion on his own,
after bypassing several more typical plot-induced paths to heroism.
But the life he thought he wanted is not the life he actually wanted,
and that propells him into re-examining his priorities and ultimately joining the good guys on his own.
Now, there are about a million other ways to turn your bad guys good,
and they basically fall in a sliding scale between all-the-villain'-decision and all-someone-else's-decision.
Zuko was on the far end of that spectrum,
but more typical cases generally lie somewhere in the middle.
The villain might change their mind thanks to a heartfelt conversation with a hero
convincing them to join their side,
or get tipped over the edge by a villain on their side going really extra villainous, causing them to re-evaluate.
Dragon Ball Z's Vegeta is a good example of a middle range transition to heroism.
You have a very, very slow journey to the side of good, and it's got almost no moral component to it.
The only thing initially motivating him is the constant assault on his pride by the fact that everyone keeps kicking his ass
because his character is basically only there to establish how extra scary these new bad guys are.
The first arc where he can be considered anything resembling a protagonist is the Frieza Arc,
which is fairly early on, but that's just an enemy-of-his-enemy desperation move.
After that, despite being largely considered a good guy,
or at least not explicitly a bad guy, by the other good guys,
He has a tendency to cause more problems than he solves, all because of his pride.
He lets Cell absorb Andriod 18 and reach perfect form to get a good fight,
and therefore directly causes every other problem in that arc,
up to and including Goku dying, almost for real this time.
In the end, it's his family that anchors him into the side of good,
for reasons that extend beyond practicality for a change.
His long-suppressed or ignored love for his son flares up when the kid takes a laser to the chest,
and it suddenly occurs, damn, that he actually doesn't want most of these people dead,
except maybe Goku sometimes.
After that, with one not-so-minor setback thanks to the pride thing again,
he pretty much slides seamlessly into grumpy aggressive heroism
thanks to the compassion he accidentally developed for the people in his life.
Which in turn is thanks to the fact that nobody in the DBZ universe bats an eyelash at rooming with someone
that spent all of last week trying and/or succeeding at murdering them and everyone they love.
Favorable circumstances allow him to become a good guy,
and despite waffling back and forth a whole bunch, he does eventually bridge the gap on his own,
with a pretty dope act of self-sacrifice that, because this is Dragon Ball, obviously isn't permanent.
The convenient thing about DBZ is that even if redemption equals death,
that usually just means they'll get to be redeemed and alive again in the space of a year at most.
Anyway, on the full other side of the spectrum from Zuko,
some villains are redeemed entirely through the actions of others,
usually because they're Evil because they've been gunked-up by some kind of pure evil essence,
and they become Good after getting evil scrubbed off by a friendship lazer or something.
That's a situation where their actual character has almost no bearing on their morality or lack thereof,
so their moral flip-flop has almost no input from them.
Also, that mostly shows up in, like, kids' cartoons.
Anyway.
So all right, we've covered a little bit of how villains can turn good.
There's playing mechanisms which we've largely categorized by how much
introspection your villain did before transitioning to the side of good,
and how much of their own decision it was.
That's all cool.
So what happens next?
See, in some universes, the heroes brush off attempted murder like it ain't no thing.
Doesn't matter if you're still swaddled in anime bandages from the last time you two interacted,
if they're ready to be a good guy, that blood loss is suspiciously rusty water under the bridge.
But in others, the heroes might reasonably be holding a grudge.
Sure, maybe the villain has changed, or maybe they haven't,
or maybe it doesn't matter because the last time you fought they punched a hole in your chest
and you're still grumpy.
These are all fair reactions from your characters. So what do you do?
Well in some cases the newly reformed villain doesn't explicitly join the heroes,
which helps reduce any lingering grumpiness.
They're not trying to join the friend group, they're just tangentially on their side.
Conversely, sometimes the reformed villain doesn't want to join the squad, but the squad drags them in anyway.
But in a lot of cases they do want to join the squad, and the squad might not feel the same way.
This can be tricky to make feel... convincing.
The longer they've been a villain, the more bad blood you potentially have between them and the good guy.
Maybe they did some really bad stuff,
and maybe at least one of the characters really doesn't want to forgive them for that stuff.
The more convincingly villainous they were before,
the harder it will be to convince the audience or the heroes that they've changed.
So this can be a slow process.
Generally, they win over the heroes gradually, maybe one or two at a time.
Or with some grand dramatic act of self-sacrifice that
demonstrates they're willing to throw everything away for their new cause.
Combining the two works pretty well, too.
Okay, so you convinced the heroes your bad guy is now a good guy,
your good guys now have some funny banter about that one time your-used-to-be-bad-guy dangled one of them off a cliff or something,
good times are had by all.
But wait! There's someone you forgot to convince.
It's your audience.
There are a number of ways you can lose your audience by turning your bad guys good.
In the simplest cases,
they might like the bad guy less now that the bad guy in question is emotionally stable
and probably not wearing quite so much black.
In some cases, the bad guy may have done some seriously heinous stuff in the past,
and while the characters might be willing to forgive and forget, the readers might not be.
This is actually a problem I had with the anime Fairy Tail.
For those of you deeper in anime circles than I am, you'll probably know better than I do
that Fairy Tail has this thing where I'd say like 90% of the early villains in that show
became heroes less than a scene later.
After, like, the third time this happened, everyone started being all
"Oh, boy, more bad guys! Can't wait to see how Natsu turns them good!"
And as a result, it almost seemed like the author felt the need to make
every season's bad guy way more evil than the previous one.
So no way would we expect them to turn good?
Oh, you thought the guy who crucified a teenage girl was bad?
Well, these guys murdered their dragon parents!
And this lady tortured the protagonist on screen,
and this guy invented black magic and uncontrollably kills everything in a 10 yard radius.
No way could any of these guys be
aw, damn it.
Now this can... pull people out of the story a little.
If the bad guys don't go anywhere, or if they do go somewhere
but that somewhere is just the ever-expanding roster of tertiary good guys,
it can get kind of old, and lose its spark.
And if the villains are too easily forgiven by the heroes,
they can pull the audience away from the heroes and make it harder to relate.
On the flipside, you can get cases where the audience wants the villain to be redeemed,
but the heroes are mistrustful.
This can also pull us away from heroes,
But instead of pulling us out of the story, it pulls us towards the former villain,
which can lead to some interesting sympathy scenarios where we've completely switched who we're rooting for.
Again, they did this with Zuko, and it was awesome.
Now, this is all basically discussing the actual process and immediate consequences
of the bad guy flipping sides.
But in the long term, there's some very interesting stuff you can do with a good guy who used to be bad.
See, in a lot of cases, the heroes don't forget that their new friend used to be a bad guy.
They might bring it up in a joking fashion, or in a not-so joking fashion if
the used-to-be-bad-guy seems to have retained some old habits from their erstwhile villainy.
And of course, on the most extreme end,
What do you do if the used-to-be-bad-guy switches back?
This is a very common story for redeemed villains, and it's easy to see why.
A villain has been redeemed by definition has a flexible sense of right and wrong.
It's very plausible both for the audience and for the heroes
that maybe they switch back and are up to their old tricks again.
There are three ways to play this.
Either they really have changed back, or they were never really good in the first place,
Or they're lying their butt off to trick both the heroes and whatever villains they've allied themselves with
relying on their impressive villainy resume to get themselves into an advantageous position
to backstab the baddie.
Of these three, the first two are kind of... eh.
I mean, they're good for what they are, and they do a darn good job of making your audience suffer,
especially if they were rooting for that character to be redeemed.
Hey, they managed to do this with Zuko, too. God, that show was good.
They're basically knife twisting.
You wanted the character to be good and they weren't,
or maybe you didn't trust the character and you hate to be proven right.
Bonus points of either of those sentiments are held by an actual protagonist.
But the third one is by far my favorite,
because if you play your cards right, you can get all the advantages of the first two
plus some seriously quality banter between the heroes when the ruse is revealed,
and at the climactic turning point, a potentially awesome reveal of the quote-unquote "bad guy"-'s true loyalties.
The difficulty here is convincing your audience that you are going for option one or two,
so that the true reveal is sufficiently revelatory.
Usually this means having your totally-a-real-bad-guy-again do something suitably nasty,
like torturing or killing someone, or just beating the tar out of one of their friends.
Which is actually done to almost humorous affect in Dragonball.
During the Boo arc, when Vegeta gets quote-unquote "taken over" by vomiting evil magic
and becomes Majin Vegeta.
This very briefly looks like he's just been possessed,
but it turns out he willingly took the evil power
because he thinks his pure evilness is the only thing that'll let him be stronger than Goku.
Now this actually is kind of him turning briefly evil again before he finally gets over himself.
But Goku absolutely does not believe that Vegeta is evil.
So to convince Goku that he's serious, he vaporizes half the stadium killing a good chunk of the onlookers.
So, evil, right?
But this is Dragonball. Literally that same day after Vegeta gets over himself,
they summon Shenron and resurrect everyone not-evil who got killed,
including everyone Vegeta wiped out during his little power-play tantrum
It was a major oh, snap moment right up until everyone remembered what show they were watching.
But it did work, because even though it was a very solvable problem,
Vegeta hadn't murdered anyone innocent in something like seven seasons.
So it was kind of a big deal.
Anyway, so basically, bottom line, villain redemption is complicated and a bit of a minefield,
but potentially very rewarding if you play with it.
So, yeah.