*THIS IS A CONCEPT, NOT A CHARACTER* http://www.giantbomb.com/boo/92-3682/
Overview
Boo first appeared in Super Mario Bros. 3 on the Nintendo Entertainment System. When looked at Boo freezes in his place because he is known for being extremely shy. When Mario is not facing boo he gains his courage and chases after him. Boo has been featured as a playable character in the Mario Kart series and other Mario spin-off games. His most fleshed out role was in the game Luigi's Mansion, where he ran a haunted house and was trying to take Luigi down throughout the game.