Boo the Ghost, while certainly not the first enemy you think of when you think of all of Super Mario's foes, is one of the most enduring and effective. Appearing in over 20 Mario games (in one form or another), Boo has made his presence known for over twenty years and is a worthy entry into the Villain Hall of Fame.
...well, he's certainly more of a badass than Pac-Man's ghosts, in any case.
