Luigi can Jump higher and is quicker than Mario. In Super Smash bros, Luigi can also hit harder than Mario. So what is Luigi hiding? Well the theory goes that Luigi is over power and he keeps it a secret, so he hides in Mario's shadow. But what I think is that Luigi knows that his power is too strong and could cause destruction to the mushroom kingdom. Then why is Luigi afraid of ghost? Well, because he not afraid of ghost, he's actually afraid of being possess by ghost, because he is afraid the ghost could use Luigi's power to harm and kill and to use for evil. *tired*