Go to the Aqua Lounge and talk to the bartender (the pink fish that serves drinks). He will talk about his squid. He will ask you to scare the person at the Den. The bartender at the Aqua Lounge also gives you a pair of scissors. Go back to Cloud Plaza and go to the Sky Tower. Enter Maru's Shop Of Stuff. He will give you a white cloth. After it is in your inventory, use the scissors to cut it to create the Ghost Suit.