I think there are two main ways to play a villain through RP. Of course the first way is the a-typical bad guy already described. The second way would be the surprise reveal. Play as one of the 'good guys' but find ways to work against them the whole time without giving it away. This requires a lot more work, but in the end when your character is revealed to the the mastermind behind it all, it's so much more fulfilling.
Of course the real problem with RPing the villain is that your character is, for all intensive purposes, a throw-away toon. Because once they become known it's very hard to change that reputation.
Of course the real problem with RPing the villain is that your character is, for all intensive purposes, a throw-away toon. Because once they become known it's very hard to change that reputation.