The Boo is one of Mario’s iconic enemies, with them being a ghost that tend to inhabit spooky or dark places. Whenever you come across a Boo, they will turn invisible and stop moving if you face them. However, turn your back to a Boo and they will start coming after you. Normally, you can’t really harm a Boo, unless you have a Super Star, but in some levels, you will have access to a flashlight on a helmet/hat. If you shine a light on a Boo long enough, you will be able to defeat a Boo.