The great thing about this week is that all the characters are new to SMB3. Most of them go on to appear in just about every Mario game that matters.
Boo is one of those enemies that in their few bytes of character exude personality. Boo’s gimmick is easy. He’s just as scared of you as you are of him. If you face your fears and look at him he’ll hide his eyes and freeze. If you run then he’ll chase you. When surrounded you’ll find yourself turning back and forth in a panic as they inch closer to you. It’s no wonder he’s was given a much bigger role in SMB World and many games long after.