[Jerry]

Most of the time, a villain is someone who's pursuing a goal that inconveniences others but for whatever reason, that doesn't stop them from pursuing it. Maybe they're justifying it to themselves somehow, rationalizing that it has to be done for the greater good of their goal- or throwing morality away entirely as a hindrance hammered into everyone at a young age to maintain a status quo that benefits the people already in charge. Or something like that. They have views and goals that run contrary to most people, so by popular opinion, they earn the label of villain.

But that's just public validation. Everyone's a villain to someone, or to be less melodramatic about it, everyone has the potential to be an antagonist to everyone else. Even if you played a saintly nun that wouldn't dream of harming anyone, always quick to apologize, and the first to offer their help to those in need, someone's going to find your existence offensive to their views on the world. That works in the opposite direction too, if you're aiming to be a villain, not everyone is going to end up recognizing what you're doing as a legitimate problem by their standards and ethics.

Some people are too edgy to care that you've kidnapped someone's kid and plan to sacrifice them to your dark god, some people are too emotionally numbed to give a hoot that you've got blackmail material or a hostage to use against them- (on some level, they might be waving it away because hey, OOC, the stakes are pretty low, there's no way anyone's going to lose their character from their inaction, someone will eventually take care of you even if they don't play ball), and some people are too radical in their views and opinions, so if you try to say, set explosive powder kegs in key positions around a major political building to goad them into submission, they may end up hailing you as a hero and urge you to blow the place up to teach the ruling class a lesson. You can't please (or upset) everyone. You can't force it, either. That leads to desperation, trying to wrangle people into corrals based on what you expect or want from them, getting upset about how little control you have and how easily it all comes tumbling down when someone decides to call your villainous bluffs, daring you to kill the hostage, or encouraging you to try blowing those bombs. They know you can't. Sigrogana Legends is a Saturday morning cartoon show; Everything has to go back to the way it was at the start of the episode for next week's episode. There can be personal consequences if you have a few people willing to bite that bullet, but I guess that's my point, scale.

The more people you involve, the more you have to worry about. You have some people who either don't have the time or patience to engage with something beyond a surface level who will show up only to big scenes for that low-investment high of getting to save the day like the heroes they love to watch, or people that just can't find it in themselves to get invested for whatever reason and who get very sarcastic and snarky about everything that happens when the context of the scene says lives are on the line. Far too cool- (or empty)- to care. Or maybe they just don't value the lives on the line, and aren't being particularly subtle about their indifference. They'll still make being antagonistic much harder for you. Suck the wind out of your sails, or pressure you to assert yourself as a villain with heckling, or try to stomp you down real quick with a dog-pile the second you're within reach or accept that first innocuous invitation to spar. I don't mean to discourage you or anyone else from playing a villain, I just think that before you romanticize the concept of being this sort of villain or that sort of villain, you should consider how big of a villain you have the patience and resources to be. You benefit greatly from having friends and supporters to play complimentary roles, as minions or heroic fall-guys to legitimize the threat you present, or other handy narrative supporting roles.

Try to keep in communication with the game's staff if you feel something you're doing or attempting to do may have narrative consequences beyond making one or two characters unhappy with you, and the event admins are happy to support you so long as it's all above board. Heck, keep in contact OOC with some of the people playing the opposing heroes even if it's going to be a long term thing. Don't go sharing spoilers or details or inviting them to stop you (unless it's contextually appropriate like a written letter of challenge you prepared in character or something), but foster a friendly relationship with them. Some times, it's easy to forget that it's all just fun and games at the end of the day, and people can get very heated about losses or perceived sleights. If people start to hate you OOC, then they may end up making trouble for you OOC in the hopes of getting back at you, and while you can report that sort of things to admins, it's better to just keep things friendly in the spirit of everyone having fun. Take Wreck-It-Ralph to heart, just because you're a "bad guy", doesn't mean you're a bad guy. (Or that you have to be one OOC, anyhow.)

Try to have fun with it too. This may all sound like doom and gloom cynic talk, but I really only intend for it to be practical advice and words of caution. If things get sour, they have a higher chance of getting sour again in the future, it quickly becomes a slippery slope and you'll find more and more of your days ending on a sour note. Everyone's here to have fun, you're no exception. If you plan to play a villain, or just "some jerk out to show low-born trash their place in the world", whatever your motivations or goals, remember to mind other people's (OOC) thoughts and feelings and to speak up if things are getting too personal or heated (OOC). If you're looking to engage with a villain, try to remember that they're not actually a horrible child-killing cannibal or whatever, they're playing a role and hamming things up. They aren't trying to cheat you or trouble you (OOC, at least), and you can politely inform them OOC if something's bothering you. (You can inform them IC too, but that'll probably just make them monologue, or let loose a villainous laugh, or something.)
Sorry if this counts as derailing the thread, I just wanted to offer practical advice.

To be more on topic, I have a hard time seeing villains as anything other than "people with controversial opinions and desires". Short of them being an alien creature with no concept or understanding of right and wrong, I imagine most villains know they're doing something wrong in their more lucid moments but like most people, will quickly sink right back into blissful self-delusion if it begins to hurt or write it off as a completely unimportant observation if it doesn't bring on any guilt. Bowser knows what he's doing is wrong, and he's shown to feel guilty about it a handful of times, but he's also very unhappy with the status quo. He's lonely, and the status quo perpetuates that. He thinks he won't be lonely if he can have Peach. Failing that, he's developed a weird antagonistic bromance with Mario, and he finds he's not lonely when he's fighting Mario to steal or keep Peach- or competing with him in a sports game, or teaming up with him in an RPG. His motivation isn't exactly two-dimensional as loneliness is complicated, it's incredibly human, a simple desire that gets twisted up and toxic as it goes unsatisfied. Like people turning to cannibalism if they get hungry enough, it's a simple need but it can become very, very twisted if it gets ignored. Then once they've done it, they can't undo it. The memory of having committed that taboo is going to haunt them until they develop coping mechanisms of some kind. They'll have sleepless nights when they remember what they did, until they make some kind of peace with it. Which usually means embracing it, and taking it to the extreme after the memories have tortured them enough. "It only hurts because I think I'm a human, because I think I'm normal. Clearly, I'm not, or I wouldn't have done it in the first place. So if I'm not human, if I'm not normal, I must be a monster, a villain, a horrible wicked thing. I'll feel better if I embrace it, and act as one of my kind should..." That colors their behavior from then on, and the guilt is slowly burnt away as they numb themselves to those first memories by making many, many more- and often times far worse ones. Not that they usually recognize that as why they don't feel guilty about it anymore.

Genetics, abuse, neglect, or the wrong kinds of lessons growing up too. Unless it's a cold, unfeeling machine that's decided to kill people for some cold, logical reason, villains are usually the heroes of their own story trying to get by and win their happiness with the hand they've been dealt, even if it means fighting the whole world. As I see it, anyhow. A rebel thinks he's fighting for his homeland with the same kind of stubborn conviction as a soldier on the opposite end of the battlefield believing the same about his own fighting. Freeza probably thought he was doing the universe a huge favor by taming the saiyans, and civilizing entire worlds by bringing them under his rule. Egotistical, sure- but his family was pretty competitive, and prideful. That was probably just the norm for him growing up, constantly proving and maintaining your constant superiority. I guess what I'm getting at is that you don't have to be a villain that sets out to be a villain. You could just be really dedicated to your work, or your heritage, or some noble goal that "just so happens to involve some sacrifices and cruelty along the way". The ends justify the means. Or you could be someone with an appetite that went unsatisfied for a little too long, that's gone off the deep-end. Like I said, everyone has the potential to be an antagonist to everyone else. Everyone's a villain to someone.