I've always wanted one. It would make a great pseudo legendary. It would start out as a little skull and as it evolves it grows into a full skeleton. It would have a balance between both special and physical ghost and fighting type moves.
Another idea would be having Ghost Nappa as a pokemon. :-)
Cuteness Overload! http://i.imgur.com/gw03gl7.png No Justice! No Peace! 3DS FC: 3394-3716-0128 Vita PSN: Queen_Sialeeds