Playing a superhero is great.  The challenge to real rp is to play the villain.  Or as some would say.  Its one thing to have thoughts of good things, and good deeds. Its very easy to want to save the world.  But what happens if you want to destroy it?  Whats your motivation?  What drives you, and what makes you tick?  Playing a villain allows you to plot and fret and brag about your master plans, all the while struggling to avoid interferance of those pesky superheroes.  You get to build deathtraps, and construct secret lairs and blackmail the world if they dont meet your eminently reasonable demands.

Being the villain means you get to design the schemes that the heroes must foil. You must choose a hideout that no one could ever find, design the superweapon that stops them when they do, and plan an escape route when your superweapon mysteriously malfunctions.  Do your research;  Find out where the heroes are most vulnerable and exploit those weaknesses. Mercy  is a trait for the weak.

Just remember, You can be evil, but there's no point in being vicious.  Plotting to take over the world is one thing, blowing up a hospital is quite another.  Brutality is nobody's idea of fun roleplaying.  If you find yourself veering in these directions,  others will most likely do everything in their power to stop your villain- and most likely try to take the villain away from you.  MARVEL's just a game after all.