When writing, there are three types of characters that I love writing for, more than any other:

1) Emperors/Empresses, or other royal types that are basically considered to be near-divine by their subjects.
2) Gods, because it's just fun to write for beings who can make their desires a reality with a thought.
3) Villains. Because villains.

So it follows, then, then if I can write for a villainous god-emperor - say, Nightmare Moon, or my take on evil Celestia - then I get to be a happy, happy author. Right?

Wrong.

...

...no, just kidding, that's absolutely right.

~The Emphatically Not Ambiguously Evil At All Evil Duo!~
Vectors by ~C-H-Loboguerrero-C (Nightmare Moon) and Qsteel (Corona)

Something is just fun about writing for villains, especially. There's just so many different ways you can go. Is the villain some kind of greedy conqueror who wants everything, and damn whomsoever is stupid enough to get in their way? Are they petty and jealous and trying to prove that they're just as good as everyone else? Are they convinced that they're the good guys and everyone else are bad guys - that they're the only sane ones in an insane world? Or - my personal favorite - are they wonderfully, gleefully evil and aware of this fact and just revel in it? In the real world, no one ever thinks of themselves as being truly evil. But in a fantasy world, you can have being who are literally composed of Evil Itself. That's just awesome.

Still, it can be tricky to do a villain right. Villains can be many things - crazy, manipulative, powerful, surprisingly nice once you get to know them - but there are two things a villain should always be.

First, a villain has to be a serious threat in the audience's eyes. The villain doesn't necessarily have to go around shoving spikes up people's posteriors Vlad Tepes style, but there should always be a sense that the villain has a legitimately good chance of achieving whatever he or she is after if the hero doesn't work to stop him or her. If the villain is a bank robber after money, for example, then the audience should see that the villain has a thought-out plan. The villain should be shown arriving well-equipped to rob the bank. Ideally, the villain should, mid-heist, encounter something that's not part of the plan, but then overcome that problem - not necessarily with ease, but certainly with a sense that it was a minor bump at best and now they're back on track. This shows the villain as being competent, which is ideal.

Second - and this is very, very important - the villain has to win on occasion, and preferably those victories are on-screen, not simply mentions offhand about how "he's conquered another planet between the last chapter and this one." (not that that's a bad idea, it's just that if those are his only victories then they're essentially meaningless to the audience).

Now, here we get tricky. If the villain's goal is nothing less than the extinction of man, then it's going to be difficult to have the villain pull this off while still leaving heroes around to fight him.

But not impossible. I hated the Majin Buu arc for being too god-damned long, but I LOVED Buu himself. He just got more destructive and more gleefully evil with each transformation and I LOVED IT.

The villain winning, of course, comes entirely from how you define "victory." Okay, so Lord Badguy did not succeed in his latest attempt to conquer the Land of Awesome. He was, however, able to destroy the Chalice of Catharsis before the good guys could drink from it and get strong enough to fight him directly! Even if the villain does not see his or her victories as being victories his or herself ("Gah! You've won this round, but I'll be back!"), the audience will, at least, see that he or she is just as capable as the good guy. Villainous victories, in the audience's mind, count for more than hero's victories. Of course the hero is going to win. He or she is the hero, and his or her victories bring us closer to a state of normallacy (whatever "normal" is in the setting). But when a villain wins? Oops. One step closer to Armageddon.

Villains that lack these two qualities - either they don't seem competent at whatever they do, or they're never shown actually winning, or both - aren't villains. They're menaces. Sure, if not for the hero, they might have conquered the world by now, but then again if not for the hero we wouldn't even be here. I'm not saying that every villain should be some kind of genre-savvy "I personally wrote half of the Evil Overlord list" clone of Xanatos or Diaboromon (or God forbid Xanatos with Diaboromon as his digimon partner) -

We're boned.

- but a villain who can't win and never seems to even stand a chance of winning just really isn't worth the reader's time as the central antagonist of your story. The bumbling idiot menace has a place, and he or she can be tons of fun to write for or watch on screen, but he or she should be a secondary antagonist or the minion of the villain, or else more of a vehicle to move the plot along without, themselves, being central to the plot (for example, the Ganggreen Gang from The Powerpuff Girls frequently filled this role). Why the villain hasn't replaced the bumbling idiots is another question entirely, but ultimately it might come back to the fact that villains are people too. Unless they're demons or undead abominations or something, in which case I guess they're not people, per se, but the point is that villains should make mistakes like anyone else, and often make the same mistake over and over. You could have your villain learn from and correct these mistakes, but I think it's better if the villain somehow manages to remain a viable threat in spite of these mistakes.

Of course, when you can get a legitimately scary, clever villain with legitimately competent minions...well, that's just a recipe for awesome.

And, apparently, one of the best villain songs ever.