3. Boo
Its no surprise that a lot of Mario enemies are based on animals. Or fungi. What about people? Takashi Tezuka is one of the most influential game designers working at Nintendo. In 1988, annoyed by the long hours he was spending at the office, Takashis normally shy and timid wife had a furious argument with him one night as he came home from work on the game. Instead of taking on board the criticism and working to appease his wife and save his troubled marriage, Takashis first thought was apparently "Damn, this gives me a great idea for Super Mario Bros 3." He promptly created Boo, a character who was nervous and harmless when you face it, but transforms into a deadly killer whenever your back is turned. Somewhat surprisingly, Takashi is still married.