well in my real mario serie the boos are still ghost lol but the way they have been send in mansions,haunted house,castles. it is a tecnologie machine who as been remade by bowser and its smartest soldiers. have invented a device that keeps the dead from passing on they place it in locations of there choise and that wave devise send strong zones that disturbes the dead and makes them all thing they wer the worst murderers and all that so they all apear in the same ghost shape and they wer called Boo's the device is called ShockWave if you destroi the devce they house or anything els there located in.they will all be free to move on so the first time you see bowser he maneges to escape leaving you no choise to cross this haunted house and thats where youl see them for the first time.in my second game in the final chapter witch is a real life story of luigis mansion you will see way more boos and other ghost(the full story of luigis mansion will be added with the characters to come) I just repainted the head witch really looks like real boo and glued it to a wall to make them look like they fly ^^they dont have little arms like nintendo in fact they apear as a creature head the its there horns that looks like little arms ^^ of course there are also the boos with the thoung coming out they can be worst then normal ones ^^