Roleplaying "Evil"

There are just as many adjectives for evil: dishonorable, deceptive, abusive, cruel, immoral, and more. As with any character, an Evil character is not necessarily at his worst, most foul and antagonistic behavior at all times. Being of an Evil disposition only means that the capacity for these things is always there and that they may know no limits to the depth of their depravity. This means that an Evil character can be charming, cooperative, and for all appearances a nice guy. But its a façade that is not likely to last long unless the character is particularly determined and capable of maintaining such a deception.

Some examples of villains:

* The Conformist - he thrives by taking advantages afforded to him by whatever system is available to do so, almost equating what is legal to what is right and proper even when it is legal to seriously harm another. After all, if it weren't right and proper, the law should be changed, and since it hasn't been changed, it must still be right.
* The Intellectual - he probably does not consider himself to be evil, but almost certainly considers himself to be intelligent, wise, shrewd, and on the ball rather than foolishly concerning himself with the welfare of others as those idiotic dopes that speak of the common good are concerned. Often, this type of character thinks of themselves as naturally superior to others, their own needs coming first, and the needs of others coming much further down the list.
* The Overlord - he is concerned only with his own goals and nothing else. Only those things that with strengthen him and push him towards that goal are important and he will pursue that goal with any means possible. He hopes to bring himself to a position of power, glory, and prestige.

Playing a villain will never grant a player license to break Blizzard's rules of conduct. Being "evil" is not a valid excuse for randomly collapsing or harassing others; and one of the most difficult aspects of upholding an "evil" character is ensuring grudges stop at your character. Don't get angry with others for their responses to your character, because they too are taking a logical role.
Tips for the Villains
Before making an evil character you should realize it can be more difficult than others, make sure you have a good idea beforehand of what your characters goals are. You most likely wont get far roleplaying an "evil" character if you cant make any friends. Allies can be beneficial even if the character doesn't use violence or warfare to exact his evilness. Lastly make sure to be convincing, in general not many people are evil. Define your character as being one of those unique few and you'll have a great time. Just remember that the Good Guys usually win.

What makes you a villain? Most characters don't just decided on a whim that they want to be evil. This should stem from your characters history and not the players desire. Be unique. Some-thing that is not often seen, or that people fear or misunderstand is often labeled "evil". Go against the grain. This means speech and mannerisms as well as appearance.

* "Evil is in the eye of the beholder." So you want to be evil to some - not all. Perhaps even most, but always have a way out. If you don't, you're setting yourself up for the fall.
* Focus. Know what it is you want to accomplish. Be open to change. Nothing stays static for too long. If it can go wrong, it will. Plan ahead. Might does not equal malevolence. You can have the biggest chakram, an infinite DreamSoul elemen, and a whole slew of offensive arts, and are still just a thug.
* Violence does not equal villainy. A politician in power can be ten times more corrupt than a convicted killer who acted in self-defense. Destruction isn't always the answer either. Hostages present a much more complicated situation than simply planting a bomb.
* Crime is not always the best avenue for those of the dark alignment. This is especially true in Underlight. Be creative and find other methods to achieve your goals.
* Morality is important. Most evil doers have compromised moral values. Either they're working for themselves and don't think the rules apply to them, or they're working for the common good but don't understand whats appropriate and whats not.
* The end can justify the means. You're playing WoW the way you see fit. If a few souls get lost along the way, what is that to compare to the lives you'll save after the fact? You can either end up the hero or a martyr if you're not careful.
* Remember that you didn't do anything wrong if you didn't get caught. And the more people that support your side of the story, the less likely you are to be labeled a "threat" to society as a whole.
* Set standards. Be prejudice. If you think one way, then others are misguided or utterly wrong. They're either agreeing with you, or they disagree with you. Don't be afraid to stand up for what you believe, and teach it to those impressionable Newly Awakened.
* Honor is for the dead. The difference between a hero and a fool is luck. The difference between a coward and a corpse? Stupidity. Live to fight another day.
* Keep your friends close and your enemies closer. Never let them see it coming. A good villain always has his/her ace in the hole; and usually the joker as well.
* Don't be afraid to ask for help in your endeavors. Just be careful what you wish for. Minions are just that. People will work for reward before friendship. Greed can be good motivation. Remember that if they see a way to use you as a stepping stone, they will. Especially if it gives them what you have.
* Take small steps at first. Test the waters. You cant be bad until you know what good is.
* Trademarks. If it's been done, it's probably been done better. Find your own path, and let that aspect be yours and yours alone. Make yourself memorable.
* Achilles' heel. Every bad guy has one. Illness. Disability. Pangs of regret. Love for family. A persistent obsession. Maybe this is what drives your character. (For undead, most people seem to test the "no feelings" aspect.)
* Turning over a new leaf. Evildoers don't make many friends. When it becomes unbearable, there are always other options. This also makes an incredibly good smoke screen.
* Don't be invulnerable! Sure, capture the heroes, make them watch you describe your master plan...but if they come up with some ingenious escape method, and disrupt your evil ritual of world domination, take it in your stride...don't just ignore it! It gets very annoying when you shield yourself with magic...again. And again. And again.
* Don't get silly and lighthearted. Villains are darkhearted and cruel.
* Well-written and well portrayed villains don't always see themselves and what they're doing as evil, even if it is working on some contraption to brutally slaughter everyone in the world (they might see it as purging the weak and unfit for a shining new world order). A villain who can (almost) convince an indirect third party (such as a reader or outside observer) that they are in the right can go a lot farther than the rampaging "Blargh! I am evil! I am the bad guy! Fear me! Hate me! MWAH-HAH-HAH-HAH!" villain. However, the key is to almost convince the reader/observer: there needs to be something about you or your plans that makes the reader/observer happy when you meet your final end.
* Anti-heroes are NOT villains, and villains are NOT anti-heroes. Anti-heroes oppose the heroes, but they also oppose the villains, but not necessarily for the same reasons. The anti-hero might have a personal vendetta or something similar against the villain (in which case, they oppose the heroes because they want to take down the villain instead) or they might oppose the villain for the same reasons as the hero, however, a difference of opinion or method makes them anti-heroes, such as the anti-hero willing to do whatever it takes (even if it costs the lives of countless innocents), while the hero would abhor such measures and methods.
* Don't always lose! Yes, the good guys are supposed to win, but only in the very end! The phrase "To be Continued..." can be a nice change of pace, and good RPers will accept it as long as you don't always win.
* Never hesitate to use the good guys to further your own agenda, such as taking out a personal enemy or getting a rare ingredient for your master scheme. Remember, the good guys are suckers: they fall for the little old lady needing help every single time it's used. Guaranteed. Or your money back. Both heroic heroes and antiheroes will fall for this. Always remember Article VI of the Villain's Handbook: There is nobody more stupid than the hero of a TV cartoon show MMORPG Roleplaying circle.
* A villain's overall agenda that results in doing something that is actually a good thing, but still has a pack of heroes on his or her tail because his or her methods are screwy, or the heroes are misinformed is more of an antihero than a villain. The Golden Sun series is a good example of this.